Skip to main content

Full text of "Reader 2 - Motion in the Heavens: Project Physics"

See other formats

The Project Physics Course 



Motion in the Heavens 

The Project Physics Course 



2 Motion in the Heavens 

A Component of the 
Project Physics Course 

Published by 


New York, Toronto 

This publication is one of the many 
instructional materials developed for the 
Project Physics Course. These materials 
include Texts, Handbooks, Teacher Resource 
Books, Readers, Programmed Instruction 
Booklets, Film Loops, Transparencies, 16mm 
films and laboratory equipment. Development 
of the course has profited from the help of 
many colleagues listed in the text units. 

Directors of Harvard Project Physics 

Gerald Holton, Department of Physics, 

Harvard University 
F. James Rutherford, Capuchino High School, 

San Bruno, California, and Harvard University 
Fletcher G. Watson, Harvard Graduate School 

of Education 

Copyright © 1970, Project Physics 

All Rights Reserved 

SBN 03-084559-9 

1234 039 98765432 

Project Physics is a registered trademark 

Picture Credits 

Cover photograph: "Variation within a Sphere, 
No. 10: The Sun." Sculptural construction of gold 
wire, 22 feet long, 11 feet high, 5V2 feet deep. 
By Richard Lippold, American sculptor. Courtesy 
of The Metropolitan Museum of Art, New York City. 

2 4 

5 I 

3 6 

Picture Credits for frontispiece 

(1) Photo by Glen J. Pearcy. 

(2) Jeune fille au corsage rouge lisant. Jean Baptiste 
Camille Corot. Painting. Collection Buhrle, Zurich. 

(3) Harvard Project Physics staff photo. 

(4) Femme lisant. Georges Seurat, Conte crayon 
drawing. Collection C. F. Stoop, London. 

(5) Portrait of Pierre Reverdy. Pablo Picasso. 
Etching. Museum of Modern Art, N.Y.C. 

(6) Lecture au lit. Paul Klee. Drawing. Paul Klee 
Foundation, Museum of Fine Arts, Berne. 

Sources and Acknowledgments 
Project Physics Reader 2 

1. Opening Scenes from The Black Cloud by Fred 
Hoyle. Reprinted with permission of Harper and 
Row, Publishers, and William Heinemann Ltd. 

2. Roll Call from Of Time and Space and Other 
Things by Isaac Asimov, copyright © 1963 by 
Mercury Press, Inc. Reprinted with permission of 
Doubleday & Company, Inc., and Dennis Dobson. 

3. A Night at the Observatory by Henry S. F. Cooper, 
Jr., copyright © 1967 by American Heritage 
Publishing Co., Inc. Reprinted by permission from 
the Summer 1967 issue of Horizon Magazine. 

4. Preface to De Revolutionibus, by Nicolaus 
Copernicus from Occasional Notes to the Royal 
Astronomical Society, No. 10, 1947. 

5. The Starry Messenger from Discoveries and 
Opinions of Galileo, translated by Stillman Drake, 
copyright © 1957 by Stillman Drake. Reprinted 

by permission of Doubleday & Company, Inc. 

6. Kepler's Celestial Music from The Birth of a New 
Physics by I. Bernard Cohen, copyright © 1960 
by Educational Services, Inc. Reprinted by 
permission of Doubleday & Company, Inc. 

7. Kepler, by Gerald Holton, copyright © 1960 by 
Scientific American. Reprinted with permission. 
All rights reserved. 

8. Kepler on Mars, by Johannes Kepler (translated 
by Owen Gingerich), copyright © 1967 by Owen 
Gingerich. Reprinted with permission. 

9. Newton and the Principia from An Essay in the 
History of Scientific Ideas by Charles Goulston 
Gillispie, copyright © 1960 by Princeton Uni- 
versity Press. Reprinted with permission. 

10. The Laws of Motion and Proposition One from 
Mathematical Principles of Natural Philosophy 
and His System of the World by Isaac Newton, 
translated by Florian Cajori. copyright © 1962 by 
University of California Press. Reprinted with 

1 1 . The Garden of Epicurus, by Anatole France from 
The Anatole France Omnibus translated by 

A. Allinson. Reprinted with permission of Dodd, 
Mead & Company, Inc., and The Bodley Head Ltd. 

12. Universal Gravitation by Richard P. Feynman, 
Robert B. Leighton, and Matthew Sands from 
The Feynman Lectures on Physics, copyright © 
1963 by Addison-Wesley Publishing Company. 
Reprinted with permission. 

13. An Appreciation of the Earth from Habitable 
Planets for Man by Stephen H. Dole, copyright © 
1964 by The Rand Corporation. Reprinted with 

14. Mariner 6 and 7 TV Pictures: Preliminary Analysis 
by R. B. Leighton and others from Science, Vol. 
166, October 3, 1969, copyright © 1969 by the 
American Association for the Advancement of 
Science. Reprinted with permission. 

15. The Boy Who Redeemed His Father's Name 
by Terry Morris from the October 1965 issue of 
Redbook, copyright © 1965 by Terry Morris. 

16. The Great Comet of 1965 by Owen Gingerich, 
copyright © 1966 by the Atlantic Monthly 
Company, Boston. Reprinted with permission. 

17. Gravity Experiments from Modern Science and 
Technology edited by Robert Colburn, copyright 
© 1965 by Litton Educational Publishing, Inc. 
Reprinted with permission of Van Nostrand 
Reinhold Company. 

18. Space, the Unconquerable from Profiles of the 
Future by Arthur C. Clarke, copyright © 1960 
by Popular Mechanics Co. Reprinted with 
permission of Harper & Row, Publishers, and 
Victor Gollancz Ltd. 

19. Is There Intelligent Life Beyond the Earth from 
Intelligent Life in the Universe by I. S. Shlovskii 
and Carl Sagan, copyright © 1966 by Holden-Day, 
Inc. Reprinted with permission. 

20. The Stars Within Twenty-two Light Years That 
Could Have Habitable Planets by Stephen H. Dole 
from Habitable Planets for Man, copyright © 1964 
by The Rand Corporation. Reprinted with 

21. Condon Report, Section 1 , Conclusions and 
Recommendations, Introduction by Walter Sullivan 
from Scientific Study of Unidentified Flying 

Objects, copyright © 1969 by The New York Times 
Company. Section 1, copyright © 1968 by the 
Board of Regents of the University of Colorado. 
Reprinted with permission of Bantam Books, Inc. 
All rights reserved. 

22. The Life-Story of a Galaxy by Margaret Burbidgt. 
from Stars and Galaxies: Birth, Aging and Death 
in the Universe, Thornton Page, Editor, copyright 
© 1962 by Prentice-Hall, Inc., Englewood Cliffs, 
N. J. Reprinted with permission. 

23. The Expansion of the Universe from Relativity 
and Common Sense: A New Approach to Einstein 
by Hermann Bondi, copyright © 1964 by Educa- 
tional Services, Inc., copyright © 1962 by 
Professor Hermann Bondi and The Illustrated 
London News & Sketch Ltd. Reprinted with 
permission of Doubleday & Company, Inc., 

and Heinemann Educational Books Ltd., from 
their title The Universe at Large. 

24. Negative Mass by Banesh Hoffmann, copyright © 
1965 by Banesh Hoffmann from Science Journal. 
Reprinted with permission. 

25. Four Poetic Fragments About Astronomy taken 
from Imagination's Other Place, Poems of Science 
and Mathematics, compiled by Helen Plotz, 

T. Y. Crowell Company, publishers, New York. 
From Troilus and Cressida by William Shake- 
speare. From Hudibras by Samuel Butler. From 
II Va Neiger Dans Quelques Jours by Francis 
Jammes. From As If, My Father's Watch, by John 
Ciardi, copyright © 1955 by the Trustees of 
Rutgers College. Reprinted by permission of 
the author. 

26. The Dyson Sphere from Intelligent Life in the 
Universe by I. S. Shlovskii and Carl Sagan, 
copyright © 1966 by Holden-Day, Inc. Reprinted 
with permission. 



This is not a physics textbook. Rather, it is a physics 
reader, a collection of some of the best articles and 
book passages on physics. A few are on historic events 
in science, others contain some particularly memorable 
description of what physicists do; still others deal with 
philosophy of science, or with the impact of scientific 
thought on the imagination of the artist. 

There are old and new classics, and also some little- 
known publications; many have been suggested for in- 
clusion because some teacher or physicist remembered 
an article with particular fondness. The majority of 
articles is not drawn from scientific papers of historic 
importance themselves, because material from many of 
these is readily available, either as quotations in the 
Project Physics text or in special collections. 

This collection is meant for your browsing. If you follow 
your own reading interests, chances are good that you 
will find here many pages that convey the joy these 
authors have in their work and the excitement of their 
ideas. If you want to follow up on interesting excerpts, 
the source list at the end of the reader will guide you 
for further reading. 

Reader 2 
Table of Contents 

1 Opening Scenes ' 

Fred Hoyle 

2 Roll Call 20 

Isaac Asimov 

3 A Night at the Observatory 34 

Henry S. F. Cooper, Jr. 

4 Preface to De Revolutionibus 43 

Nicolaus Copernicus 

5 The Starry Messenger 47 

Galileo Galilei 

6 Kepler's Celestial Music 49 

I. Bernard Cohen 

7 Kepler 

Gerald Holton 

8 Kepler on Mars 

Johannes Kepler 

1 1 The Garden of Epicurus 

Anatole France 

13 An Appreciation of the Earth 

Stephen H. Dole 

1 4 Mariners 6 and 7 Television Pictures: 
Preliminary Analysis. 

R. B. Leighton and others 



9 Newton and the Principia 68 

C. C. Gillispie 

1 The Laws of Motion, and Proposition One 74 

Isaac Newton 


1 2 Universal Gravitation 87 

Richard P. Feynman, Robert B. Leighton, and Matthew Sands 




15 The Boy Who Redeemed His Father's Name 116 

Terry Morris 

16 The Great Comet of 1965 122 

Owen Gingerich 

17 Gravity Experiments 128 

R. H. Dicke, P. G. Roll, and J. Weber 

1 8 Space The Unconquerable 1 34 

Arthur C. Clarke 

19 Is There Intelligent Life Beyond the Earth? 1 44 

I. S. Shklovskii and Carl Sagan 

20 The Stars Within Twenty-Two Light Years That Could Have 1 50 
Habitable Planets 

Stephen Dole 

21 Scientific Study of Unidentified Flying Objects 152 

Edward U. Condon and Walter Sullivan 

22 The Life-Story of a Galaxy 1 67 

Margaret Burbidge 

23 Expansion of the Universe 1 92 

Hermann Bondi 

24 Negative Mass 197 

Banesh Hoffmann 

25 Four Poetic Fragments About Astronomy 202 

From Troilus and Cressida William Shakespeare 

From Hudibras Samuel Butler 

My Father's Watch John Ciardi 

II Va Neiger . . . Francis Jammes 

26 The Dyson Sphere 206 

I. S. Shklovskii and Carl Sagan 


In this introductory chapter to his science fiction novel, 
The Black C/oud, the noted astronomer Fred Hoyle gives a 
realistic picture of what goes on within an astronomy 
laboratory. The emphasis is on experimental astronomy. 

Opening Scenes 

Fred Hoyle 

A chapter from his book The Black Cloud, 1957. 

It was eight o'clock along the Greenwich 
meridian. In England the wintry sun of 7th January, 1964, 
was just rising. Throughout the length and breadth of the 
land people were shivering in ill-heated houses as they 
read the morning papers, ate their breakfasts, and grumbled 
about the weather, which, truth to tell, had been appalling 
of late. 

The Greenwich meridian southward passes through 
western France, over the snow-covered Pyrenees and 
through the eastern corner of Spain. The line then sweeps 
to the west of the Balearic Islands, where wise people 
from the north were spending winter holidays — on a beach 
in Minorca a laughing party might have been seen return- 
ing from an early morning bathe. And so to North Africa 
and the Sahara. 

The primary meridian then swings towards the equator 
through French Sudan, Ashanti, and the Gold Coast, where 
new aluminium plants were going up along the Volta 
River. Thence into a vast stretch of ocean, unbroken until 
Antarctica is reached. Expeditions from a dozen nations 
were rubbing elbows with each other there. 

All the land to the east of this line, as far as New Zea- 
land, was turned towards the Sun. In Australia, evening was 
approaching. Long shadows were cast across the cricket 
ground at Sydney. The last overs of the day were being 
bowled in a match between New South Wales and Queens- 

land. In Java, fishermen were busying themselves in prep- 
aration for the coming night's work. 

Over much of the huge expanse of the Pacific, over Amer- 
ica, and over the Atlantic it was night. It was three a.m. in 
New York. The city was blazing with light, and there was 
still a good deal of traffic in spite of recent snow and a cold 
wind from the north-west. And nowhere on the Earth at 
that moment was there more activity than in Los Angeles. 
The evening was still young there, twelve o'clock: the 
boulevards were crowded, cars raced along the freeways, 
restaurants were still pretty full. 

A hundred and twenty miles to the south the astronomers 
on Mount Palomar had already begun their night's work. 
But although the night was clear and stars were sparkling 
from horizon to zenith, conditions from the point of view 
of the professional astronomer were poor, the 'seeing' was 
bad — there was too much wind at high levels. So nobody 
was sorry to down tools for the midnight snack. Earlier in 
the evening, when the outlook for the night already looked 
pretty dubious, they had agreed to meet in the dome of the 
48-inch Schmidt. 

Paul Rogers walked the four hundred yards or so from 
the 200-inch telescope to the Schmidt, only to find Bert 
Emerson was already at work on a bowl of soup. Andy and 
Jim, the night assistants, were busy at the cooking stove. 

"Sorry I got started," said Emerson, "but it looks as 
though tonight's going to be a complete write-off." 

Emerson was working on a special survey of the sky, and 
only good observing conditions were suitable for his work. 

"Bert, you're a lucky fellow. It looks as though you're 
going to get another early night." 

"I'll keep on for another hour or so. Then if there's 
no improvement I'll turn in." 

"Soup, bread and jam, sardines, and coffee," said 
Andy. "What'll you have?" 

"A bowl of soup and cup of coffee, thanks," said 

"What're you going to do on the 200-inch? Use the 
jiggle camera?" 

"Yes, I can get along tonight pretty well. There's sev- 
eral transfers that I want to get done." 

They were interrupted by Knut Jensen, who had walked 
the somewhat greater distance from the 18-inch Schmidt. 

Opening Scenes 

He was greeted by Emerson. 

"Hello, Knut, there's soup, bread and jam, sardines, 
and Andy's coffee." 

"I think I'll start with soup and sardines, please." 

The young Norwegian, who was a bit of a leg-puller, 
took a bowl of cream of tomato, and proceeded to empty 
half a dozen sardines into it. The others looked on in 

"Judas, the boy must be hungry," said Jim. 

Knut looked up, apparently in some surprise. 

"You don't eat sardines like this? Ah, then you don't 
know the real way to eat sardines. Try it, you'll like it." 

Then having created something of an effect, he added: 

"I thought I smelled a skunk around just before I came 

"Should go well with that concoction you're eating, 
Knut," said Rogers. 

When the laugh had died away, Jim asked: 

"Did you hear about the skunk we had a fortnight ago? 
He degassed himself near the 200-inch air intake. Before 
anybody could stop the pump the place was full of the 
stuff. It sure was some hundred per cent stink. There must 
have been the best part of two hundred visitors inside the 
dome at the time." 

"Lucky we don't charge for admission," chuckled Em- 
erson, "otherwise the Observatory 'd be sunk in for com- 

"But unlucky for the clothes cleaners," added Rogers. 

On the way back to the 18-inch Schmidt, Jensen stood 
listening to the wind in the trees on the north side of the 
mountain. Similarities to his native hills set off an irrepres- 
sible wave of homesickness, longing to be with his family 
again, longing to be with Greta. At twenty-four, he was in 
the United States on a two-year studentship. He walked on, 
trying to kick himself out of what he felt to be a ridiculous 
mood. Rationally he had no cause whatsoever to be dispir- 
ited. Everyone treated him with great kindness, and he had 
a job ideally suited to a beginner. 

Astronomy is kind in its treatment of the beginner. 
There are many jobs to be done, jobs that can lead to 
important results but which do not require great experi- 
ence. Jensen's was one of these. He was searching for 
supernovae, stars that explode with uncanny violence. 

Within the next year he might reasonably hope to find one 
or two. Since there was no telling when an outburst might 
occur, nor where in the sky the exploding star might be 
situated, the only thing to do was to keep on photo- 
graphing the whole sky, night after night, month after 
month. Some day he would strike lucky. It was true that 
should he find a supernova located not too far away in the 
depths of space, then more experienced hands than his 
would take over the work. Instead of the 18-inch Schmidt, 
the full power of the great 200-inch would then be directed 
to revealing the spectacular secrets of these strange stars. 
But at all events he would have the honour of first discov- 
ery. And the experience he was gaining in the world's 
greatest observatory would stand well in his favour when he 
returned home — there were good hopes of a job. Then he 
and Greta could get married. So what on earth was he 
worried about? He cursed himself for a fool to be unnerved 
by a wind on the mountainside. 

By this time he had reached the hut where the little 
Schmidt was housed. Letting himself in, he first consulted 
his notebook to find the next section of the sky due to be 
photographed. Then he set the appropriate direction, south 
of the constellation of Orion: mid-winter was the only time 
of the year when this particular region could be reached. 
The next step was to start the exposure. All that remained 
was to wait until the alarm clock should signal its end. 
There was nothing to do except sit waiting in the dark, to 
let his mind wander where it listed. 

Jensen worked through to dawn, following one exposure 
by another. Even so his work was not at an end. He had 
still to develop the plates that had accumulated during the 
night. This needed careful attention. A slip at this stage 
would lose much hard work, and was not to be thought of. 

Normally he would have been spared this last exacting 
task. Normally he would have retired to the dormitory, 
slept for five or six hours, breakfasted at noon, and only 
then would he have tackled the developing job. But this 
was the end of his 'run.' The moon was now rising in the 
evening, and this meant the end of observing for a fort- 
night, since the supernova search could not be carried on 
during the half of the month when the moon was in the 
night sky — it was simply that the moon gave so much light 

Opening Scenes 

that the sensitive plates he was using would have been 
hopelessly fogged. 

So on this particular day he would be returning to the 
Observatory offices in Pasadena, a hundred and twenty-five 
miles away. The transport to Pasadena left at half-past 
eleven, and the developing must be done before then. Jen- 
sen decided that it would be best done immediately. Then 
he would have four hours sleep, a quick breakfast, and be 
ready for the trip back to town. 

It worked out as he had planned, but it was a very tired 
young man who travelled north that day in the Observatory 
transport. There were three of them: the driver, Rogers, 
and Jensen. Emerson's run had still another two nights to 
go. Jensen's friends in wind-blown, snow-wrapped Norway 
would have been surprised to learn that he slept as the car 
sped through the miles of orange groves that flanked the 

Jensen slept late the following morning and it wasn't until 
eleven that he reached the Observatory offices. He had 
about a week's work in front of him, examining the plates 
taken during the last fortnight. What he had to do was to 
compare his latest observations with other plates that he 
had taken in the previous month. And this he had to do 
separately for each bit of the sky. 

So on this late January morning of 8th January, 1964, 
Jensen was down in the basement of the Observatory 
buildings setting up an instrument known as the 'blinker.' 
As its name implies, the 'blinker' was a device that 
enabled him to look first at one plate, then at the other, 
then back to the first one again, and so on in fairly rapid 
succession. When this was done, any star that had changed 
appreciably during the time interval between the taking of 
the two plates stood out as an oscillating or 'blinking' 
point of light, while on the other hand the vast majority of 
stars that had not changed remained quite steady. In this 
way it was possible to pick out with comparative ease the 
one star in ten thousand or so that had changed. Enormous 
labour was therefore saved because every single star did not 
have to be examined separately. 

Great care was needed in preparing plates for use in the 
'blinker.' They must not only be taken with the same 

instrument, but so far as possible must be shot under iden- 
tical conditions. They must have the same exposure times 
and their development must be as similar as the observing 
astronomer can contrive. This explains why Jensen had 
been so careful about his exposures and development. 

His difficulty now was that exploding stars are not the 
only sort to show changes. Although the great majority of 
stars do not change, there are a number of brands of oscil- 
lating stars, all of which 'blink' in the manner just de- 
scribed. Such ordinary oscillators had to be checked sepa- 
rately and eliminated from the search. Jensen had esti- 
mated that he would probably have to check and eliminate 
the best part of ten thousand ordinary oscillators before he 
found one supernova. Mostly he would reject a 'blinker' 
after a short examination, but sometimes there were doubt- 
ful cases. Then he would have to resort to a star catalogue, 
and this meant measuring up the exact position of the star 
in question. So all in all there was quite a bit of work to do 
before he got through his pile of plates — work that was not 
a little tedious. 

By 14th January he had nearly finished the whole pile. 
In the evening he decided to go back to the Observatory. 
The afternoon he had spent at the California Institute of 
Technology, where there had been an interesting seminar 
on the subject of the spiral arms of the galaxies. There had 
been quite a discussion after the seminar. Indeed he and his 
friends had argued throughout dinner about it and during 
the drive back to the Observatory. He reckoned he would 
just about get through the last batch of plates, the ones he 
had taken on the night of 7th January. 

He finished the first of the batch. It turned out a finicking 
job. Once again, every one of the 'possibilities' resolved 
into an ordinary, known oscillator. He would be glad when 
the job was done. Better to be on the mountain at the end 
of a telescope than straining his eyes with this damned 
instrument, he thought, as he bent down to the eye-piece. 
He pressed the switch and the second pair flashed up in the 
field of view. An instant later Jensen was fumbling at the 
plates, pulling them out of their holders. He took them 
over to the light, examined them for a long time, then 
replaced them in the blinker, and switched on again. In a 
rich star field was a large, almost exactly circular, dark 

Opening Scenes 

patch. But it was the ring of stars surrounding the patch 
that he found so astonishing. There they were, oscillating, 
blinking, all of them. Why? He could think, of no satisfac- 
tory answer to the question, for he had never seen or heard 
of anything like this before. 

Jensen found himself unable to continue with the job. 
He was too excited about this singular discovery. He felt he 
simply must talk to someone about it. The obvious man of 
course was Dr. Marlowe, one of the senior staff members. 
Most astronomers specialise on one or other of the many 
facets of their subject. Marlowe had his specialities too, but 
he was above all a man of immense general knowledge. 
Perhaps because of this he made fewer mistakes than most 
people. He was ready to talk astronomy at all hours of the 
day and night, and he would talk with intense enthusiasm 
to anyone, whether a distinguished scientist like himself or 
a young man at the threshold of his career. It was natural 
therefore that Jensen should wish to tell Marlowe about his 
curious find. 

He carefully put the two plates in question in a box, 
switched off the electrical equipment and the lights in the 
basement, and made his way to the notice board outside the 
library. The next step was to consult the observing list. He 
found to his satisfaction that Marlowe was not away either 
at Palomar or Mount Wilson. But, of course, he might have 
gone out for the evening. Jensen's luck was in, however, 
for a phone call soon elicited that Marlowe was at home. 
When he explained that he wanted to talk to him about 
something queer that had turned up, Marlowe said: 

"Come right over, Knut, I'll be expecting you. No, it's 
all right. I wasn't doing anything particular." 

It says much for Jensen's state of mind that he rang for 
a taxi to take him to Marlowe's house. A student with an 
annual emolument of two thousand dollars does not nor- 
mally travel by taxi. This was particularly so in Jensen's 
case. Economy was important to him because he wished to 
travel around the different observatories in the United 
States before he returned to Norway, and he had presents 
to buy, too. But on this occasion the matter of money never 
entered his head. He rode up to Altadena, clutching his 
box of plates, and wondered whether in some way he'd 
made a fool of himself. Had he made some stupid mistake? 

Marlowe was waiting. 

"Come right in," he said. "Have a drink. You take it 
strong in Norway, don't you?" 

Knut smiled. 

"Not so strong as you take it, Dr. Marlowe." 

Marlowe motioned Jensen to an easy chair by the log fire 
(so beloved by many who live in centrally heated houses), 
and after moving a large cat from a second chair, sat down 

"Lucky you rang, Knut. My wife's out for the evening, 
and I was wondering what to do with myself." 

Then, typically, he plunged straight to the issue — diplo- 
macy and political finesse were unknown to him. 

"Well, what've you got there?" he said, nodding at the 
yellow box that Jensen had brought. 

Somewhat sheepishly, Knut took out the first of his two 
pictures, one taken on 9th December, 1963, and handed it 
over without comment. He was soon gratified by the reac- 

"My God!" exclaimed Marlowe. "Taken with the 18- 
inch, I expect. Yes, I see you've got it marked on the side 
of the plate." 

"Is there anything wrong, do you think?" 

"Nothing so far as I can see." Marlowe took a magni- 
fying glass out of his pocket and scanned carefully over the 

"Looks perfectly all right. No plate defects." 

"Tell me why you're so surprised, Dr. Marlowe." 

"Well, isn't this what you wanted me to look at?" 

"Not by itself. It's the comparison with a second plate 
that I took a month later that looks so odd." 

"But this first one is singular enough," said Marlowe. 
"You've had it lying in your drawer for a month! Pity 
you didn't show it to me right away. But of course, you 
weren't to know." 

"I don't see why you're so surprised by this one plate 

"Well, look at this dark circular patch. It's obviously a 
dark cloud obscuring the light from the stars that lie be- 
yond it. Such globules are not uncommon in the Milky 
Way, but usually they're tiny things. My God, look at this! 
It's huge, it must be the best part of two and a half degrees 
across 1" 

Opening Scenes 

"But, Dr. Marlowe, there are lots of clouds bigger than 
this, especially in the region of Sagittarius." 

"If you look carefully at what seem like very big clouds, 
you'll find them to be built up of lots of much smaller 
clouds. This thing you've got here seems, on the other 
hand, to be just one single spherical cloud. What really 
surprises me is how I could have missed anything as big as 

Marlowe looked again at the markings on the plate. 

"It is true that it's in the south, and we're not so 
concerned with the winter sky. Even so, I don't see how I 
could have missed it when I was working on the Trapezium 
in Orion. That was only three or four years ago and I 
wouldn't have forgotten anything like this." 

Marlowe's failure to identify the cloud — for this is un- 
doubtedly what it was — came as a surprise to Jensen. Mar- 
lowe knew the sky and all the strange objects to be found 
in it as well as he knew the streets and avenues of Pasa- 

Marlowe went over to the sideboard to renew the drinks. 
When he came back, Jensen said: 

"It was this second plate that puzzled me." 

Marlowe had not looked at it for ten seconds before he 
was back to the first plate. His experienced eye needed no 
'blinker' to see that in the first plate the cloud was sur- 
rounded by a ring of stars that were either absent or nearly 
absent in the second plate. He continued to gaze thought- 
fully at the two plates. 

"There was nothing unusual about the way you took 
these pictures?" 

"Not so far as I know." 

"They certainly look all right, but you can never be 
quite sure." 

Marlowe broke off abruptly and stood up. Now, as al- 
ways when he was excited or agitated, he blew out enor- 
mous clouds of aniseed-scented tobacco smoke, a South Af- 
rican variety. Jensen marvelled that the bowl of his pipe 
did not burst into flames. 

"Something crazy may have happened. The best thing 
we can do is to get another plate shot straight away. I 
wonder who is on the mountain tonight." 

"You mean Mount Wilson or Palomar?" 

"Mount Wilson. Palomar's too far." 

"Well, as far as I remember one of the visiting astron- 
omers is using the 100-inch. I think. Harvey Smith is on 
the 60-inch." 

"Look, it would probably be best if I went up myself. 
Harvey won't mind letting me have a few moments. I 
won't be able to get the whole nebulosity of course, but I 
can get some of the star fields at the edge. Do you know the 
exact co-ordinates?" 

"No. I phoned as soon as I'd tried the plates in the 
'blink.' I didn't stop to measure them." 

"Well, never mind, we can do that on the way. But 
there's no real need to keep you out of bed, Knut. Why 
don't I drop you at your apartment? I'll leave a note for 
Mary saying I won't be back until sometime tomorrow." 

Jensen was excited when Marlowe dropped him at his 
lodging. Before he turned in that night he wrote letters 
home, one to his parents telling them very briefly of the 
unusual discovery, and another to Greta saying that he 
believed that he'd stumbled on something important. 

Marlowe drove to the Observatory offices. His first step was 
to get Mount Wilson on the phone and to talk to Harvey 
Smith. When he heard Smith's soft southern accent, he 

"This is Geoff Marlowe. Look, Harvey, something 
pretty queer has turned up, so queer that I'm wondering if 
you'd let me have the 60-inch for tonight. What is it? I 
don't know what it is. That's just what I want to find out. 
It's to do with young Jensen's work. Come down here at 
ten o'clock tomorrow and I'll be able to tell you more 
about it. If you're bored I'll stand you a bottle of Scotch. 
That's good enough for you? Finel Tell the night assistant 
that I'll be up at about one o'clock, will you?" 

Marlowe next put through a call to Bill Barnett of Cal- 

"Bill, this is Geoff Marlowe ringing from the offices. I 
wanted to tell you that there'll be a pretty important 
meeting here tomorrow morning at ten o'clock. I'd like 
you to come along and to bring a few theoreticians along. 
They don't need to be astronomers. Bring several bright 
boys. . . . No I can't explain now. I'll know more tomor- 
row. I'm going on the 60-inch tonight. But I'll tell you 
what, if you think by lunch-time tomorrow that I've got 


Opening Scenes 

you out on a wild-goose chase, I'll stand you a crate of 
Scotch. . . . Fine!" 

He hummed with excitement as he hurried down to the 
basement where Jensen had been working earlier in the 
evening. He spent some three-quarters of an hour measur- 
ing Jensen's plates. When at last he was satisfied that he 
would know exactly where to point the telescope, he went 
out, climbed into his car, and drove off towards Mount 

Dr. Herrick, the Director of the Observatory, was aston- 
ished to find Marlowe waiting for him when he reached his 
office at seven-thirty the following morning. It was the Di- 
rector's habit to start his day some two hours before the 
main body of his staff, "in order to get some work 
done," as he used to say. At the other extreme, Marlowe 
usually did not put in an appearance until ten-thirty, and 
sometimes later still. This day, however, Marlowe was sit- 
ting at his desk, carefully examining a pile of about a dozen 
positive prints. Herrick's surprise was not lessened when he 
heard what Marlowe had to say. The two men spent the 
next hour and a half in earnest conversation. At about nine 
o'clock they slipped out for a quick breakfast, and re- 
turned in time to make preparations for a meeting to be 
held in the library at ten o'clock. 

When Bill Barnett's party of five arrived they found 
some dozen members of the Observatory already assembled, 
including Jensen, Rogers, Emerson and Harvey Smith. A 
blackboard had been fitted up and a screen and lantern for 
showing slides. The only member of Barnett's party who 
had to be introduced round was Dave Weichart. Marlowe, 
who had heard a number of reports of the abilities of this 
brilliant twenty-seven-year-old physicist, noted that Barnett 
had evidently done his best to bring a bright boy along. 

"The best thing I can do," began Marlowe, "is to 
explain things in a chronological way, starting with the 
plates that Knut Jensen brought to my house last night. 
When I've shown them you'll see why this emergency 
meeting was called." 

Emerson, who was working the lantern, put in a slide 
that Marlowe had made up from Jensen's first plate, the 
one taken on the night of 9th December, 1963. 


"The centre of the dark blob," went on Marlowe, "is 
in Right Ascension 5 hours 49 minutes, Declination minus 
30 degrees 16 minutes, as near as I can judge." 

"A fine example of a Bok globule," said Barnett. 

"How big is it?" 

"About two and a half degrees across." 

There were gasps from several of the astronomers. 

"Geoff, you can keep your bottle of whisky," said 
Harvey Smith. 

"And my crate, too," added Bill Barnett amidst the 
general laughter. 

"I reckon you'll be needing the whisky when you see 
the next plate. Bert, keep rocking the two backwards and 
forwards, so that we can get some idea of a comparison," 
went on Marlowe. 

"It's fantastic," burst out Rogers, "it looks as if there's a 
whole ring of oscillating stars surrounding the cloud. But 
how could that be?" 

"It can't," answered Marlowe. "That's what I saw 
straight away. Even if we admit the unlikely hypothesis that 
this cloud is surrounded by a halo of variable stars, it is 
surely quite inconceivable that they'd all oscillate in phase 
with each other, all up together as in the first slide, and all 
down together in the second." 

"No, that's preposterous," broke in Barnett. "If we're 
to take it that there's been no slip-up in the photography, 
then surely there's only one possible explanation. The cloud 
is moving towards us. In the second slide it's nearer to us, 
and therefore it's obscuring more of the distant stars. At 
what interval apart were the two plates taken?" 

"Rather less than a month." 

"Then there must be something wrong with the photog- 

"That's exactly the way I reasoned last night. But as I 
couldn't see anything wrong with the plates, the obvious 
thing was to take some new pictures. If a month made all 
that difference between Jensen's first plate and his second, 
then the effect should have been easily detectable in a 
week — Jensen's last plate was taken on 7th January. Yester- 
day was 14th January. So I rushed up to Mount Wilson, 
bullied Harvey off the 60-inch, and spent the night photo- 
graphing the edges of the cloud. I've got a whole collection 
of new slides here. They're not of course on the same scale 


Opening Scenes 

as Jensen's plates, but you'll be able to see pretty well 
what's happening. Put them through one by one, Bert, and 
keep referring back to Jensen's plate of 7th January." 

There was almost dead silence for the next quarter of an 
hour, as the star fields on the edge of the cloud were care- 
fully compared by the assembled astronomers. At the end 
Barnett said: 

"I give up. As far as I'm concerned there isn't a 
shadow of a doubt but that this cloud is travelling towards 

And it was clear that he had expressed the conviction of 
the meeting. The stars at the edge of the cloud were being 
steadily blacked out as it advanced towards the solar system. 

"Actually there's no doubt at all about it," went on 
Marlowe. "When I discussed things with Dr. Herrick ear- 
lier this morning he pointed out that we have a photograph 
taken twenty years ago of this part of the sky." 

Herrick produced the photograph. 

"We haven't had time to make up a slide," said he, 
"so you will have to hand it round. You can see the black 
cloud, but it's small on this picture, no more than a tiny 
globule. I've marked it with an arrow." 

He handed the picture to Emerson who, after passing it 
to Harvey Smith, said: 

"It's certainly grown enormously over the twenty years. 
I'm a bit apprehensive about what's going to happen in 
the next twenty. It seems as if it might cover the whole 
constellation of Orion. Pretty soon astronomers will be out 
of business." 

It was then that Dave Weichart spoke up for the first 

"I've two questions that I'd like to ask. The first is 
about the position of the cloud. As I understand what 
you've said, the cloud is growing in its apparent size be- 
cause it's getting nearer to us. That's clear enough. But 
what I'd like to know is whether the centre of the cloud is 
staying in the same position, or does it seem to be moving 
against the background of the stars?" 

"A very good question. The centre seems, over the last 
twenty years, to have moved very little relative to the star 
field," answered Herrick. 

"Then that means the cloud is coming dead at the solar 


Weichart was used to thinking more quickly than other 
people, so when he saw hesitation to accept his conclusion, 
he went to the blackboard. 

"I can make it clear with a picture. Here's the Earth. 
Let's suppose first that the cloud is moving dead towards us, 
like this, from A to B. Then at B the cloud will look bigger 
but its centre will be in the same direction. This is the case 
that apparently corresponds pretty well to the observed 

Sarth 3 A 

There was a general murmur of assent, so Weichart went 

"Now let's suppose that the cloud is moving sideways, 
as well as towards us, and let's suppose that the motion 
sideways is about as fast as the motion towards us. Then the 
cloud will move about like this. Now if you consider the 
motion from A to B you'll see that there are two effects — 
the cloud will seem bigger at B than it was at A, exactly as 
in the previous case, but now the centre will have moved. 
And it will move through the angle AEB which must be 
something of the order of thirty degrees." 

"I don't think the centre has moved through an angle 
of more than a quarter of a degree," remarked Marlowe. 

"Then the sideways motion can't be more than about 
one per cent of the motion towards us. It looks as though 
the cloud is heading towards the solar system like a bullet 
at a target." 

"You mean, Dave, that there's no chance of the cloud 
missing the solar system, of it being a near-miss, let us say?" 

directum ofmotim of cloud 


Opening Scenes 

"On the facts as they've been given to us that cloud is 
going to score a bull's eye, plumb in the middle of the 
target. Remember that it's already two and a half degrees 
in diameter. The transverse velocity would have to be as 
much as ten per cent or so of the radial velocity if it were 
to miss us. And that would imply a far greater angular 
motion of the centre than Dr. Marlowe says has taken 
place. The other question I'd like to ask is, why wasn't the 
cloud detected sooner? I don't want to be rude about it, 
but it seems very surprising that it wasn't picked up quite 
a while ago, say ten years ago." 

"That of course was the first thing that sprang to my 
mind," answered Marlowe. "It seemed so astonishing that 
I could scarcely credit the validity of Jensen's work. But 
then I saw a number of reasons. If a bright nova or a 
supernova were to flash out in the sky it would immediately 
be detected by thousands of ordinary people, let alone by 
astronomers. But this is not something bright, it's some- 
thing dark, and that's not so easy to pick up — a dark patch 
is pretty well camouflaged against the sky Of course if one 
of the stars that has been hidden by the cloud had hap- 
pened to be a bright fellow it would have been spotted. 
The disappearance of a bright star is not so easy to detect 
as the appearance of a new bright star, but it would nev- 
ertheless have been noticed by thousands of professional 
and amateur astronomers. It happened, however, that all 
the stars near the cloud are telescopic, none brighter than 
eighth magnitude. That's the first mischance. Then you 
must know that in order to get good seeing conditions we 
prefer to work on objects near the zenith, whereas this 
cloud lies rather low in our sky. So we would naturally tend 
to avoid that part of the sky unless it happened to contain 
some particularly interesting material, which by a second 
mischance (if we exclude the case of the cloud) it does not. 
It is true that to observatories in the southern hemisphere 
the cloud would be high in the sky, but observatories in the 
southern hemisphere are hard put to it with their small 
staffs to get through a host of important problems con- 
nected with the Magellanic Clouds and the nucleus of the 
Galaxy. The cloud had to be detected sooner or later. It 


turned out to be later, but it might have been sooner. 
That's all I can say." 

"It's too late to worry about that now," said the Di- 
rector. "Our next step must be to measure the speed with 
which the cloud is moving towards us. Marlowe and I have 
had a long talk about it, and we think it should be possible. 
Stars on the fringe of the cloud are partially obscured, as 
the plates taken by Marlowe last night show. Their spec- 
trum should show absorption lines due to the cloud, and 
the Doppler shift will give us the speed." 

"Then it should be possible to calculate how long the 
cloud will be before it reaches us," joined in Barnett. "I 
must say I don't like the look of things. The way the cloud 
has increased its angular diameter during the last twenty 
years makes it look as if it'll be on top of us within fifty or 
sixty years. How long do you think it'll take to get a 
Doppler shift?" 

"Perhaps about a week. It shouldn't be a difficult job." 

"Sorry I don't understand all this," broke in Weichart. 
"I don't see why you need the speed of the cloud. You can 
calculate straight away how long the cloud is going to take 
to reach us. Here, let me do it. My guess is that the answer 
will turn out at much less than fifty years." 

For the second time Weichart left his seat, went to the 
blackboard, and cleaned off his previous drawings. 

"Could we have Jensen's two slides again please?" 

When Emerson had flashed them up, first one and then 
the other, Weichart asked: "Could you estimate how much 
larger the cloud is in the second slide?" 

"I would say about five per cent larger. It may be a little 
more or a little less, but certainly not very far away from 
that," answered Marlowe. 

"Right," Weichart continued, "let's begin by defining a 
few symbols." 

Then followed a somewhat lengthy calculation at the 
end of which Weichart announced: 

"And so you see that the black cloud will be here by 
August, 1965, or possibly sooner if some of the present esti- 
mates have to be corrected." 

Then he stood back from the blackboard, checking 
through his mathematical argument. 

"It certainly looks all right — very straightforward in fact," 


Opening Scenes 

said Marlowe, putting out great volumes of smoke.* 

"Yes, it seems unimpeachably correct," answered Wei- 

At the end of Weichart's astonishing calculation, the Di- 
rector had thought it wise to caution the whole meeting to 
secrecy. Whether they were right or wrong, no good could 
come of talking outside the Observatory, not even at home. 
Once the spark was struck the story would spread like wild- 
fire, and would be in the papers in next to no time. The 
Director had never had any cause to think highly of news- 
paper reporters, particularly of their scientific accuracy. 

From mid-day to two o'clock he sat alone in his office, 
wrestling with the most difficult situation he had ever ex- 

* The details of Weichart's remarks and work while at the black- 
board were as follows: 

"Write a for the present angular diameter of the cloud, measured 
in radians, 

d for the linear diameter of the cloud, 

D for its distance away from us, 

V for its velocity of approach, 

T for the time required for it to reach the solar system. 

To make a start, evidently we have a — d/D 

Differentiate this equation with respect to time / and we get 

da _ -ddD 

dt D 2 dt 

_ Tr dD . da d Tr 

But V = ' so that we can write — = — V. 

dt dt D 2 

Also we have — = T. Hence we can get rid of V, arriving at 

da m d 

dt DT 

This is turning out easier than I thought. Here's the answer already 

T- dt 

The last step is to approximate — by finite intervals, > where 

da Aa 

At = 1 month corresponding to the time difference between Dr. 
Jensen's two plates; and from what Dr. Marlowe has estimated Aa 

is about 5 per cent of a, i.e. = 20. Therefore T = 20 A< = 20 




perienced. It was utterly antipathetic to his nature to an- 
nounce any result or to take steps on the basis of a result 
until it had been repeatedly checked and cross-checked. Yet 
would it be right for him to maintain silence for a fortnight 
or more? It would be two or three weeks at least before 
every facet of the matter were fully investigated. Could he 
afford the time? For perhaps the tenth time he worked 
through Weichart's argument. He could see no flaw in it. 

At length he called in his secretary. 

"Please will you ask Caltech to fix me a seat on the night 
plane to Washington, the one that leaves about nine 
o'clock. Then get Dr. Ferguson on the phone." 

James Ferguson was a big noise in the National Science 
Foundation, controlling all the activities of the Foundation 
in physics, astronomy, and mathematics. He had been much 
surprised at Herrick's phone call of the previous day. It 
was quite unlike Herrick to fix appointments at one day's 

"I can't imagine what can have bitten Herrick," he 
told his wife at breakfast, "to come chasing over to Wash- 
ington like this. He was quite insistent about it. Sounded 
agitated, so I said I'd pick him up at the airport." 

"Well, an occasional mystery is good for the system," 
said his wife. "You'll know soon enough." 

On the way from the airport to the city, Herrick would 
commit himself to nothing but conventional trivialities. It 
was not until he was in Ferguson's office that he came to 
the issue. 

"There's no danger of us being overheard, I sup- 

"Goodness, man, is it as serious as that? Wait a min- 

Ferguson lifted the phone. 

"Amy, will you please see that I'm not interrupted — no, 
no phone calls — well, perhaps for an hour, perhaps two, I 
don't know." 

Quietly and logically Herrick then explained the situa- 
tion. When Ferguson had spent some time looking at the 
photographs, Herrick said: 

"You see the predicament. If we announce the business 
and we turn out to be wrong then we shall look awful 
fools. If we spend a month testing all the details and it 
turns out that we are right then we should be blamed for 


Opening Scenes 

procrastination and delay." 

"You certainly would, like an old hen sitting on a bad 


"Well, James, I thought you have had a great deal of 
experience in dealing with people. I felt you were someone 
I could turn to for advice. What do you suggest I should 

Ferguson was silent for a little while. Then he said: 

"I can see that this may turn out to be a grave matter. 
And I don't like taking grave decisions any more than you 
do, Dick, certainly not on the spur of the moment. What I 
suggest is this. Go back to your hotel and sleep through the 
afternoon — I don't expect you had much sleep last night. 
We can meet again for an early dinner, and by then I'll 
have had an opportunity to think things over. I'll try to 
reach some conclusion." 

Ferguson was as good as his word. When he and Herrick 
had started their evening meal, in a quiet restaurant of his 
choice, Ferguson began: 

"I think I've got things sorted out fairly well. It 
doesn't seem to me to make sense wasting another month 
in making sure of your position. The case seems to be very 
sound as it is, and you can never be quite certain — it would 
be a matter of converting a ninety-nine per cent certainty 
into a ninety-nine point nine per cent certainty. And that 
isn't worth the loss of time. On the other hand you are ill- 
prepared to go to the White House just at the moment. 
According to your own account you and your men have 
spent less than a day on the job so far. Surely there are a 
good many other things you might get ideas about. More 
exactly, how long is it going to take the cloud to get here? 
What will its effects be when it does get here? That sort of 

"My advice is to go straight back to Pasadena, get your 
team together, and aim to write a report within a week, 
setting out the situation as you see it. Get all your men to 
sign it — so that there's no question of the tale getting 
round of a mad Director. And then come back to Wash- 

"In the meantime I'll get things moving at this end. It 
isn't a bit of good in a case like this starting at the bottom 
by whispering into the ear of some Congressman. The only 
thing to do is to go straight to the President. I'll try to 
smooth your path there." 


This pleasant introduction to the planets and the solar system 
is by a writer well known as a scientist, a popularizer of 
science, and a writer of science fiction. Asimov approaches the 
solar system historically, briefly considering the discovery 
of some of the planets. 

Roll Call 

Isaac Asimov 

A chapter trom his book Of Time and Space and Other Things, 1963. 

When all the world was young (and I was a teen-ager), one way 
to give a science fiction story a good title was to make use of the 
name of some heavenly body. Among my own first few science 
fiction stories, for instance, were such items as "Marooned off 
Vesta," "Christmas on Ganymede," and "The Callistan Menace." 
(Real swinging titles, man!) 

This has gone out of fashion, alas, but the fact remains that in 
the 1930's, a whole generation of science fiction fans grew up 
with the names of the bodies of the Solar System as familiar to 
them as the names of the American states. Ten to one they didn't 
know why the names were what they were, or how they came to 
be applied to the bodies of the Solar System or even, in some 
cases, how they were pronounced— but who cared? When a ten- 
tacled monster came from Umbriel or Io, how much more im- 
pressive that was than if it had merely come from Philadelphia. 

But ignorance must be battled. Let us, therefore, take up the 
matter of the names, call the roll of the Solar System in the order 
(more or less) in which the names were applied, and see what 
sense can be made of them. 

The Earth itself should come first, I suppose. Earth is an old 
Teutonic word, but it is one of the glories of the English language 
that we always turn to the classic tongues as well. The Greek 
word for Earth was Gala or, in Latin spelling, Gaea. This gives 
us "geography" ("earth-writing"), "geology" ("earth-discourse"), 
"geometry" ("earth-measure"), and so on. 

The Latin word is Terra. In science fiction stories a human be- 
ing from Earth may be an "Earthling" or an "Earthman," but he 
is frequently a "Terrestrial," while a creature from another world 
is almost invariably an "extra-Terrestrial." 


Roll Call 

The Romans also referred to the Earth as Tellus Mater 
("Mother Earth" is what it means). The genitive form of tellus 
is telluris, so Earthmen are occasionally referred to in si. stories 
as "Tellurians." There is also a chemical element "tellurium," 
named in honor of this version of the name of our planet. 

But putting Earth to one side, the first two heavenly bodies to 
have been noticed were, undoubtedly and obviously, the Sun and 
the Moon, which, like Earth, are old Teutonic words. 

To the Greeks the Sun was Helios, and to the Romans it was 
Sol. For ourselves, Helios is almost gone, although we have "he- 
lium" as the name of an element originally found in the Sun, 
"heliotrope" ("sun-turn") for the sunflower, and so on. 

Sol persists better. The common adjective derived from "sun" 
may be "sunny," but the scholarly one is "solar." We may speak of 
a sunny day and a sunny disposition, but never of the "Sunny 
System." It is always the "Solar System." In science fiction, the 
Sun is often spoken of as Sol, and the Earth may even be referred 
to as "Sol III." 

The Greek word for the Moon is Selene, and the Latin word is 
Luna. The first lingers on in the name of the chemical element 
"selenium," which was named for the Moon. And the study of 
the Moon's surface features may be called "selenography." The 
Latin name appears in the common adjective, however, so that 
one speaks of a "lunar crescent" or a "lunar eclipse." Also, be- 
cause of the theory that exposure to the light of the full Moon 
drove men crazy ("moon-struck"), we obtained the word "lun- 

I have a theory that the notion of naming the heavenly bodies 
after mythological characters did not originate with the Greeks, 
but that it was a deliberate piece of copycattishness. 

To be sure, one speaks of Helios as the god of the Sun and 
Gaea as the goddess of the Earth, but it seems obvious to me that 
the words came first, to express the physical objects, and that 
these were personified into gods and goddesses later on. 


The later Greeks did, in fact, feel this lack of mythological 
character and tried to make Apollo the god of the Sun and Arte- 
mis (Diana to the Romans) the goddess of the Moon. This may 
have taken hold of the Greek scholars but not of the ordinary folk, 
for whom Sun and Moon remained Helios and Selene. (Never- 
theless, the influence of this Greek attempt on later scholars was 
such that no other important heavenly body was named for 
Apollo and Artemis.) 

I would like to clinch this theory of mine, now, by taking up 
another heavenly body. 

After the Sun and Moon, the next bodies to be recognized as 
important individual entities must surely have been the five 
bright "stars" whose positions with respect to the real stars were 
not fixed and which therefore, along with the Sun and the Moon, 
were called planets (see Chapter 4). 

The brightest of these "stars" is the one we call Venus, and it 
must have been the first one noticed— but not necessarily as an 
individual. Venus sometimes appears in the evening after sunset, 
and sometimes in the morning before sunrise, depending on 
which part of its orbit it happens to occupy. It is therefore the 
"Evening Star" sometimes and the "Morning Star" at other times. 
To the early Greeks, these seemed two separate objects and each 
was given a name. 

The Evening Star, which always appeared in the west near the 
setting Sun, was named Hesperos ("evening" or "west"). The 
equivalent Latin name was Vesper. The Morning Star was named 
Phosphoros ("light-bringer"), for when the Morning Star ap- 
peared the Sun and its light were not far behind. (The chemical 
element "phosphorus"— Latin spelling— was so named because it 
glowed in the dark as the result of slow combination with oxy- 
gen.) The Latin name for the Morning Star was Lucifer, which 
also means "light-bringer." 

Now notice that the Greeks made no use of mythology here. 
Their words for the Evening Star and Morning Star were logical, 
descriptive words. But then (during the sixth century B.C.) the 
Greek scholar, Pythagoras of Samos, arrived back in the Greek 


Roll Call 

world after his travels in Babylonia. He brought with him a skull- 
full of Babylonian notions. 

At the time, Babylonian astronomy was well developed and far 
in advance of the Greek bare beginnings. The Babylonian inter- 
est in astronomy was chiefly astrological in nature and so it 
seemed natural for them to equate the powerful planets with the 
powerful gods. (Since both had power over human beings, why 
not?) The Babylonians knew that the Evening Star and the 
Morning Star were a single planet— after all, they never appeared 
on the same day; if one was present, the other was absent, and 
it was clear from their movements that the Morning Star passed 
the Sun and became the Evening Star and vice versa. Since the 
planet representing both was so bright and beautiful, the Baby- 
lonians very logically felt it appropriate to equate it with Ishtar, 
their goddess of beauty and love. 

Pythagoras brought back to Greece this Babylonian knowl- 
edge of the oneness of the Evening and Morning Star, and Hes- 
peros and Phosphoros vanished from the heavens. Instead, the 
Babylonian system was copied and the planet was named for the 
Greek goddess of beauty and love, Aphrodite. To the Romans 
this was their corresponding goddess Venus, and so it is to us. 

Thus, the habit of naming heavenly bodies for gods and god- 
desses was, it seems to me, deliberately copied from the Baby- 
lonians (and their predecessors) by the Greeks. 

The name "Venus," by the way, represents a problem. Adjec- 
tives from these classical words have to be taken from the genitive 
case and the genitive form of "Venus" is Veneris. (Hence, "vener- 
able" for anything worth the respect paid by the Romans to the 
goddess; and because the Romans respected old age, "venerable" 
came to be applied to old men rather than young women.) 

So we cannot speak of "Venusian atmosphere" or "Venutian 
atmosphere" as science fiction writers sometimes do. We must 
say "Venerian atmosphere." Unfortunately, this has uncomforta- 
ble associations and it is not used. We might turn back to the 
Greek name but the genitive form there is Aphrodisiakos, and 
if we speak of the "Aphrodisiac atmosphere" I think we will give 
a false impression. 


But something must be done. We are actually exploring the 
atmosphere of Venus with space probes and some adjective is 
needed. Fortunately, there is a way out. The Venus cult was very 
prominent in early days in a small island south of Greece. It was 
called Kythera (Cythera in Latin spelling) so that Aphrodite 
was referred to, poetically, as the "Cytherean goddess." Our po- 
etic astronomers have therefore taken to speaking of the "Cyther- 
ean atmosphere." 

The other four planets present no problem. The second bright- 
est planet is truly the king planet. Venus may be brighter but it is 
confined to the near neighborhood of the Sun and is never seen 
at midnight. The second brightest, however, can shine through 
all the hours of night and so it should fittingly be named for the 
chief god. The Babylonians accordingly named it "Marduk." The 
Greeks followed suit and called it "Zeus," and the Romans named 
it Jupiter. The genitive form of Jupiter is Jovis, so that we speak 
of the "Jovian satellites." A person born under the astrological 
influence of Jupiter is "jovial." 

Then there is a reddish planet and red is obviously the color 
of blood; that is, of war and conflict. The Babylonians named 
this planet "Nergal" after their god of war, and the Greeks again 
followed suit by naming it "Ares" after theirs. Astronomers who 
study the surface features of the planet are therefore studying 
"areography." The Latins used their god of war, Mars, for the 
planet. The genitive form is Martis, so we can speak of the "Mar- 
tian canals." 

The planet nearest the Sun, appears, like Venus, as both an 
evening star and morning star. Being smaller and less reflective 
than Venus, as well as closer to the Sun, it is much harder to see. 
By the time the Greeks got around to naming it, the mythologi- 
cal notion had taken hold. The evening star manifestation was 
named "Hermes," and the morning star one "Apollo." 

The latter name is obvious enough, since the later Greeks as- 
sociated Apollo with the Sun, and by the time the planet Apollo 
was in the sky the Sun was due very shortly. Because the planet 
was closer to the Sun than any other planet (though, of course, 


Roll Call 

the Greeks did not know this was the reason), it moved more 
quickly against the stars than any object but the Moon. This 
made it resemble the wing-footed messenger of the gods, Hermes. 
But giving the planet two names was a matter of conservatism. 
With the Venus matter straightened out, Hermes/Apollo was 
quickly reduced to a single planet and Apollo was dropped. The 
Romans named it "Mercurius," which was their equivalent of 
Hermes, and we call it Mercury. The quick journey of Mercury 
across the stars is like the lively behavior of droplets of quick- 
silver, which came to be called "mercury," too, and we know the 
type of personality that is described as "mercurial." 

There is one planet left. This is the most slowly moving of all 
the planets known to the ancient Greeks (being the farthest from 
the Sun) and so they gave it the name of an ancient god, one 
who would be expected to move in grave and solemn steps. They 
called it "Cronos," the father of Zeus and ruler of the universe 
before the successful revolt of the Olympians under Zeus's leader- 
ship. The Romans gave it the name of a god they considered the 
equivalent of Cronos and called it "Satumus," which to us is 
Saturn. People born under Saturn are supposed to reflect its grav- 
ity and are "saturnine." 

For two thousand years the Earth, Sun, Moon, Mercury, 
Venus, Mars, Jupiter, and Saturn remained the only known bod- 
ies of the Solar System. Then came 1610 and the Italian astrono- 
mer Galileo Galilei, who built himself a telescope and turned it 
on the heavens. In no time at all he found four subsidiary objects 
circling the planet Jupiter. (The German astronomer Johann 
Kepler promptly named such subsidiary bodies "satellites," from 
a Latin word for the hangers-on of some powerful man.) 

There was a question as to what to name the new bodies. The 
mythological names of the planets had hung on into the Chris- 
tian era, but I imagine there must have been some natural hesi- 
tation about using heathen gods for new bodies. Galileo himself 
felt it wise to honor Cosimo Medici II, Grand Duke of Tuscany 
from whom he expected (and later received) a position, and 
called them Sidera Medicea (the Medicean stars). Fortunately 


this didn't stick. Nowadays we call the four satellites the "Galilean 
satellites" as a group, but individually we use mythological 
names after all. A German astronomer, Simon Marius, gave them 
these names after having discovered the satellites one day later 
than Galileo. 

The names are all in honor of Jupiter's (Zeus's) loves, of 
which there were many. Working outward from Jupiter, the first 
is Io (two syllables please, eye'oh), a maiden whom Zeus turned 
into a heifer to hide her from his wife's jealousy. The second is 
Europa, whom Zeus in the form of a bull abducted from the 
coast of Phoenicia in Asia and carried to Crete (which is how 
Europe received its name). The third is Ganymede, a young 
Trojan lad (well, the Greeks were liberal about such things) 
whom Zeus abducted by assuming the guise of an eagle. And the 
fourth is Callisto, a nymph whom Zeus's wife caught and turned 
into a bear. 

As it happens, naming the third satellite for a male rather than 
for a female turned out to be appropriate, for Ganymede is the 
largest of the Galilean satellites and, indeed, is the largest of any 
satellite in the Solar System. (It is even larger than Mercury, the 
smallest planet.) 

The naming of the Galilean satellites established once and for 
all the convention that bodies of the Solar System were to be 
named mythologically, and except in highly unusual instances 
this custom has been followed since. 

In 1655 the Dutch astronomer Christian Huygens discovered 
a satellite of Saturn (now known to be the sixth from the planet). 
He named it Titan. In a way this was appropriate, for Saturn 
(Cronos) and his brothers and sisters, who ruled the Universe 
before Zeus took over, were referred to collectively as "Titans." 
However, since the name refers to a group of beings and not to 
an individual being, its use is unfortunate. The name was ap- 
propriate in a second fashion, too. "Titan" has come to mean 
"giant" because the Titans and their allies were pictured by the 
Greeks as being of superhuman size (whence the word "titanic"), 


Roll Call 

and it turned out that Titan was one of the largest satellites in 
the Solar System. 

The Italian-French astronomer Gian Domenico Cassini was a 
little more precise than Huygens had been. Between 1671 and 
1684 he discovered four more satellites of Saturn, and these he 
named after individual Titans and Titanesses. The satellites now 
known to be 3rd, 4th, and 5th from Saturn he named Tethys, 
Dione, and Rhea, after three sisters of Saturn. Rhea was Saturn's 
wife as well. The 8th satellite from Saturn he named Iapetus after 
one of Saturn's brothers. (Iapetus is frequently mispronounced. 
In English it is "eye-ap'ih-tus.") Here finally the Greek names 
were used, chiefly because there were no Latin equivalents, ex- 
cept for Rhea. There the Latin equivalent is Ops. Cassini tried to 
lump the four satellites he had discovered under the name of 
"Ludovici" after his patron, Louis XIV— Ludovicus, in Latin— 
but that second attempt to honor royalty also failed. 

And so within 75 years after the discovery of the telescope, 
nine new bodies of the Solar System were discovered, four satel- 
lites of Jupiter and five of Saturn. Then something more exciting 
turned up. 

On March 13, 1781, a German-English astronomer, William 
Herschel, surveying the heavens, found what he thought was a 
comet. This, however, proved quickly to be no comet at all, but 
a new planet with an orbit outside that of Saturn. 

There arose a serious problem as to what to name the new 
planet, the first to be discovered in historic times. Herschel him- 
self called it "Georgium Sidus" ("George's star") after his patron, 
George III of England, but this third attempt to honor royalty 
failed. Many astronomers felt it should be named for the discov- 
erer and called it "Herschel." Mythology, however, won out. 

The German astronomer Johann Bode came up with a truly 
classical suggestion. He felt the planets ought to make a heavenly 
family. The three innermost planets (excluding the Earth) were 
Mercury, Venus, and Mars, who were siblings, and children of 
Jupiter, whose orbit lay outside theirs. Jupiter in turn was the son 
of Saturn, whose orbit lay outside his. Since the new planet had 


an orbit outside Saturn's, why not name it for Uranus, god of the 
sky and father of Saturn? The suggestion was accepted and 
Uranus* it was. What's more, in 1798 a German chemist, Mar- 
tin Heinrich Klaproth, discovered a new element he named in its 
honor as "uranium." 

In 1787 Herschel went on to discover Uranus's two largest 
satellites (the 4th and 5th from the planet, we now know). He 
named them from mythology, but not from Graeco-Roman myth- 
ology. Perhaps, as a naturalized Englishman, he felt 200 per cent 
English (it's that way, sometimes) so he turned to English folk- 
tales and named the satellites Titania and Oberon, after the 
queen and king of the fairies (who make an appearance, nota- 
bly, in Shakespeare's A Midsummer Night's Dream). 

In 1789 he went on to discover two more satellites of Saturn 
(the two closest to the planet) and here too he disrupted mytho- 
logical logic. The planet and the five satellites then known were 
all named for various Titans and Titanesses (plus the collective 
name, Titan). Herschel named his two Mimas and Enceladus 
(en-sel'a-dus) after two of the giants who rose in rebellion 
against Zeus long after the defeat of the Titans. 

After the discovery of Uranus, astronomers climbed hungrily 
upon the discover-a-planet bandwagon and searched particularly 
in the unusually large gap between Mars and Jupiter. The first 
to find a body there was the Italian astronomer Giuseppe Piazzi. 
From his observatory at Palermo, Sicily he made his first sight- 
ing on January 1, 1801. 

Although a priest, he adhered to the mythological convention 
and named the new body Ceres, after the tutelary goddess of his 
native Sicily. She was a sister of Jupiter and the goddess of grain 
(hence "cereal") and agriculture. This was the second planet to 
receive a feminine name (Venus was the first, of course) and it 
set a fashion. Ceres turned out to be a small body (485 miles in 
diameter), and many more were found in the gap between Mars 

* Uranus is pronounced "yoo'ruh-nus." I spent almost all my life accenting 
the second syllable and no one ever corrected me. I just happened to be reading 
Webster's Unabridged one day . . . 


Roll Call 

and Jupiter. For a hundred years, all the bodies so discovered 
were given feminine names. 

Three "planetoids" were discovered in addition to Ceres over 
the next six years. Two were named Juno and Vesta after Ceres' 
two sisters. They were also the sisters of Jupiter, of course, and 
Juno was his wife as well. The remaining planetoid was named 
Pallas, one of the alternate names for Athena, daughter of Zeus 
(Jupiter) and therefore a niece of Ceres. (Two chemical ele- 
ments discovered in that decade were named "cerium" and "pal- 
ladium" after Ceres and Pallas.) 

Later planetoids were named after a variety of minor god- 
desses, such as Hebe, the cupbearer of the gods, Iris, their mes- 
senger, the various Muses, Graces, Horae, nymphs, and so on. 
Eventually the list was pretty well exhausted and planetoids be- 
gan to receive trivial and foolish names. We won't bother with 

New excitement came in 1846. The motions of Uranus were 
slightly erratic, and from them the Frenchman Urbain J. J. Lever- 
rier and the Englishman John Couch Adams calculated the posi- 
tion of a planet beyond Uranus, the gravitational attraction of 
which would account for Uranus's anomalous motion. The planet 
was discovered in that position. 

Once again there was difficulty in the naming. Bode's mytho- 
logical family concept could not be carried on, for Uranus was 
the first god to come out of chaos and had no father. Some sug- 
gested the planet be named for Leverrier. Wiser council pre- 
vailed. The new planet, rather greenish in its appearance, was 
named Neptune after the god of the sea. 

(Leverrier also calculated the possible existence of a planet 
inside the orbit of Mercury and named it Vulcan, after the god 
of fire and the forge, a natural reference to the planet's close- 
ness to the central fire of the Solar System. However, such a 
planet was never discovered and undoubtedly does not exist. ) 

As soon as Neptune was discovered, the English astronomer 
William Lassell turned his telescope upon it and discovered a 
large satellite which he named Triton, appropriately enough, 


since Triton was a demigod of the sea and a son of Neptune 

In 1851 Lassell discovered two more satellites of Uranus, 
closer to the planet than Herschel's Oberon and Titania. Las- 
sell, also English, decided to continue Herschel's English folk- 
lore bit. He turned to Alexander Pope's The Rape of the Lock, 
wherein were two elfish characters, Ariel and Umbriel, and these 
names were given to the satellites. 

More satellites were turning up. Saturn was already known to 
have seven satellites, and in 1848 the American astronomer 
George P. Bond discovered an eighth; in 1898 the American 
astronomer William H. Pickering discovered a ninth and com- 
pleted the list. These were named Hyperion and Phoebe after a 
Titan and Titaness. Pickering also thought he had discovered a 
tenth in 1905, and named it Themis, after another Titaness, but 
this proved to be mistaken. 

In 1877 the American astronomer Asaph Hall, waiting for an 
unusually close approach of Mars, studied its surroundings care- 
fully and discovered two tiny satellites, which he named Phobos 
("fear") and Deimos ("terror"), two sons of Mars (Ares) in 
Greek legend, though obviously mere personifications of the in- 
evitable consequences of Mars's pastime of war. 

In 1892 another American astronomer, Edward E. Barnard, 
discovered a fifth satellite of Jupiter, closer than the Galilean 
satellites. For a long time it received no name, being called "Jupi- 
ter V" (the fifth to be discovered) or "Barnard's satellite." Myth- 
ologically, however, it was given the name Amalthea by the 
French astronomer Camille Flammarion, and this is coming into 
more common use. I am glad of this. Amalthea was the nurse of 
Jupiter (Zeus) in his infancy, and it is pleasant to have the nurse 
of his childhood closer to him than the various girl and boy 
friends of his maturer years. 

In the twentieth century no less than seven more Jovian satel- 
lites were discovered, all far out, all quite small, all probably 
captured planetoids, all nameless. Unofficial names have been 
proposed. Of these, the three planetoids nearest Jupiter bear 


Roll Call 

the names Hestia, Hera, and Demeter, after the Greek names of 
the three sisters of Jupiter (Zeus). Hera, of course, is his wife 
as well. Under the Roman versions of the names (Vesta, Juno, 
and Ceres, respectively) all three are planetoids. The two far- 
thest are Poseidon and Hades, the two brothers of Jupiter 
(Zeus). The Roman version of Poseidon's name (Neptune) is 
applied to a planet. Of the remaining satellites, one is Pan, a 
grandson of Jupiter (Zeus), and the other is Adrastea, another 
of the nurses of his infancy. 

The name of Jupiter's (Zeus's) wife, Hera, is thus applied to 
a satellite much farther and smaller than those commemorating 
four of his extracurricular affairs. I'm not sure that this is right, 
but I imagine astronomers understand these things better than I 

In 1898 the German astronomer G. Witt discovered an un- 
usual planetoid, one with an orbit that lay closer to the Sun than 
did any other of the then-known planetoids. It inched past Mars 
and came rather close to Earth's orbit. Not counting the Earth, 
this planetoid might be viewed as passing between Mars and 
Venus and therefore Witt gave it the name of Eros, the god of 
love, and the son of Mars (Ares) and Venus (Aphrodite). 

This started a new convention, that of giving planetoids with 
odd orbits masculine names. For instance, the planetoids that cir- 
cle in Jupiter's orbit all received the names of masculine par- 
ticipants in the Trojan war: Achilles, Hector, Patroclus, Ajax, 
Diomedes, Agamemnon, Priamus, Nestor, Odysseus, Antilochus, 
Aeneas, Anchises, and Troilus. 

A particularly interesting case arose in 1948, when the Ger- 
man-American astronomer Walter Baade discovered a planetoid 
that penetrated more closely to the Sun than even Mercury did. 
He named it Icarus, after the mythical character who flew too 
close to the Sun, so that the wax holding the feathers of his artifi- 
cial wings melted, with the result that he fell to his death. 

Two last satellites were discovered. In 1948 a Dutch- Ameri- 
can astronomer, Gerard P. Kuiper, discovered an innermost 
satellite of Uranus. Since Ariel (the next innermost) is a char- 


acter in William Shakespeare's The Tempest as well as in Pope's 
The Rape of the Lock, free association led Kuiper to the heroine 
of The Tempest and he named the new satellite Miranda. 

In 1950 he discovered a second satellite of Neptune. The first 
satellite, Triton, represents not only the name of a particular 
demigod, but of a whole class of merman-like demigods of the 
sea. Kuiper named the second, then, after a whole class of mer- 
maid-like nymphs of the sea, Nereid. 

Meanwhile, during the first decades of the twentieth century, 
the American astronomer Percival Lowell was searching for a 
ninth planet beyond Neptune. He died in 1916 without having 
succeeded but in 1930, from his observatory and in his spirit, 
Clyde W. Tombaugh made the discovery. 

The new planet was named Pluto, after the god of the Un- 
derworld, as was appropriate since it was the planet farthest 
removed from the light of the Sun. (And in 1940, when two ele- 
ments were found beyond uranium, they were named "neptu- 
nium" and "plutonium," after Neptune and Pluto, the two planets 
beyond Uranus.) 

Notice, though, that the first two letters of "Pluto" are the 
initials of Percival Lowell. And so, finally, an astronomer got 
his name attached to a planet. Where Herschel and Leverrier 
had failed, Percival Lowell had succeeded, at least by initial, and 
under cover of the mythological conventions. 



What is it like to work at a major observatory? A re- 
porter spends a night on Mt. Palomar talking about 
astronomy with Dr. Jesse L. Greenstein as he photo- 
graphs star spectra with the 200-inch telescope. 

3 A Night at the Observatory 

Henry S. F. Cooper, Jr. 

An article from Horizon, 1967. 


A Night at the Observatory 

A year ago last summer, I was in- 
vited out to Mount Palomar, the 
big observatory in southern California, 
to spend a night on the two-hundred- 
inch telescope. A member of the observ- 
atory's staff wrote me exuberantly, 
"The scientists here feel that the last 
couple of years have been the most ex- 
citing in astronomy since Galileo." He 
was referring to observations of the 
quasars, most of which had been made 
at Mount Palomar. Quasars are thought 
to be tremendously distant objects that 
may be almost as old as the universe 
itself; as yet, not a great deal is known 
about them. "Dr. Jesse L. Greenstein. 
Executive Officer of the Department of 
Astronomy at Cal Tech, will be going 
down to Palomar soon, and he says he 
will be glad to have you go along," my 
correspondent continued. "He says to 
warn you not to expect any great dis- 
coveries." That was an acceptable con- 
dition. As a final admonition, he added 
that the telescope is extremely delicate, 
and before I went out I had to promise 
to do my best not to break it. This, I 
thought, would be an easy promise to 
keep, since the telescope is as big as a 
small freighter. 

On my way to Palomar, I stopped 
in Pasadena at the California Institute 
of Technology, which runs the observ- 
atory. A smog that made one's eyes 
smart hung over the city. I found that 
Dr. Greenstein was already at Palomar, 
a hundred and thirty-five miles to the 
south and fifty-six hundred feet up in 
the clearer, cooler air. I headed south, 
too. The road wound through ranches 
and forest up and up a mountain. Soon 
I saw across a valley, perched on the 
edge of a plateau, the glistening alumi- 
num dome of the observatory. The 
huge slit for the telescope to peer 
through was shut like a closed eyelid. 

On top of the plateau, which was 

The huge Hale telescope, seen from the floor 
of the Palomar observatory in the "fish-eye" 
photograph opposite, is the largest reflecting 
telescope in the world. Its 200-inch mirror is 
at lower left; at right, silhouetted by a patch 
of sky. is the elevator to the prime-focus cage. 

dotted with nine sturdy yellow cot- 
tages, I headed toward the Monastery, 
where I expected to find Dr. Green- 
stein. The Monastery is the dormitory 
where the astronomers stay when they 
are using the two-hundred-inch tele- 
scope or the smaller forty-eight-inch 
Schmidt telescope. The Monastery is a 
solid building fitted out with black 
leather blinds for daytime sleeping. It 
was six o'clock in the evening. Dr. 
Greenstein, who had been up all the 
night before, was in the dining room 
having a solitary supper; a stocky, 
graying man in his mid-fifties who 
sported a tiny, pencil-thin moustache, 
he was the only astronomer on the 
mountain. Dr. Greenstein complained 
about not being able to sleep. "The 
first night I'm down here, I can't sleep 
at all," he said. "It isn't until the fifth 
day that I get a full night's, or rather 
morning's, sleep, and then it's time to 
go back to Pasadena." I asked him 
how often he had to go through this 
sleepless state, and he answered that in 
his case it was about thirty-five nights 
a year. 

"I get up here whenever I can," he 
went on, planting an elbow next to a 
half-empty coffee cup. '.'Time on the 
telescope is so valuable that you snatch 
at it whenever you can get it. Just hav- 
ing the two-hundred-inch telescope 
puts Cal Tech in a tough spot. It's a 
national asset, so we can't do anything 
trivial. Any reasonably good astrono- 
mer would have to try hard in order 
not to make an interesting discovery 
with it. In practice it is used mainly by 
the members of the Department of 
Astronomy, and even with just sixteen 
of us, we are forever feuding to get 
time on the telescope. Cloudy time can 
be a real disaster." 

I said I hoped Dr. Greenstein 
wouldn't be clouded out tonight, and 
he replied that he didn't think he would 
be. Since he had some preparations to 
make for the evening's work, I accom- 
panied him along a path from the 
Monastery through a dry, prickly field 
toward the dome. It was partially hid- 
den over the brow of a hill; for all any- 

one could tell, a big silver balloon had 
crash-landed there. 

I asked Dr. Greenstein whether he 
had been involved with quasars lately. 
He shrugged. "I feel that my work, 
which is mostly the composition of 
stars within our galaxy, is more im- 
portant; and current interpretations of 
quasars may be obsolete by next week." 
Although Dr. Greenstein is best known 
for his studies of the evolution of stars 
and galaxies, and of the elements within 
the stars, he is a top quasar man, too, 
and he has made observations to learn 
what their composition might be. 

Quasars were first noticed in 1960 by 
radio astronomers as invisible sources 
of radio waves. One of these sources, 
3C-48, was identified with what ap- 
peared to be a tiny, sixteenth-magni- 
tude star. Three years later Dr. Maarten 
Schmidt, at Palomar, managed to con- 
centrate on film enough of the feeble 
light from a quasar to get a spectrum. 
It appeared that quasars were not tiny 
stars within our own galaxy, as had 
been thought, but instead probably 
were intense and incredibly distant 
sources of light and radio waves. 
Quasar 3C-48 appears to be almost 
four billion light-years away, and sub- 
sequently other quasars have been 
measured out to almost nine billion 
light-years away; this is four-fifths of 
the way back to the "big bang" with 
which the universe supposedly began. 

By studying the quasars, it may be 
possible to learn whether the universe 
will expand indefinitely; or whether it 
will stop some day; or whether it will 
fall back in upon itself for another big 
bang— and if so, when these events will 
take place. But a great deal more in- 
formation is needed about the quasars, 
including the answer to why they shine 
so much more brightly than even the 
brightest galaxies. This is a problem 
that Dr. Greenstein is working on. 

"As it happens, I don't like working 
with quasars," Dr. Greenstein con- 
tinued as we trudged along. "They're 
tricky little things. I don't even like 
the word 'quasar.' It was invented by 
a Chinese astronomer in New York 


who doesn't speak English well. Chi- 
nese is like Hebrew, which has no 
vowels. He saw the letters QSRS, which 
stand for quasi-stellar radio source, on 
a chart, and called them 'quasars.' We 
shouldn't have a vocabulary for what 
we don't know, and when we do know 
what the quasars are, we will have a 
better word for them. Quasar sounds 
as if it's short for quasi-star, and that's 
the one thing we know a quasar isn't." 
Dr. Greenstein observed that the sky, 
darkening fast now, was beautifully 
clear. The moon, about half full, was 
rising in the east, clear crystal against 
the dark blue background, which. Dr. 
Greenstein said, augured well for seeing 
tonight. The setting sun glinted red on 
the dome. Dr. Greenstein glanced at 

the cirrus clouds in the west, which 
were reddening as the sun sank. "Sun- 
sets are nice," he said, "but you haven't 
seen anything until you see a sunrise at 

The dome, which is nine stories tall 
and as much as that in diameter, rises 
from a round, yellow, cement drum. 
Dr. Greenstein fitted a key in a latch, 
and soon we were blinking our eyes 
inside a cavernous, pitch-black room 
three stories below the telescope. Dr. 
Greenstein said he had some work to 
do in his darkroom and suggested I go 
to the third floor and take a look at the 

The inside of the dome was stuffy, 
dim, mysterious, and silent except for 
the echo of some approaching foot- 

ln operation the Hale telescope resembles 
nothing so much as a large bucket made to 
gather light The mirror collects light and 
bounces it fifty-five feet up to a focal point 
where the prime-focus cage is located For 
spectrographic analysis, the light is reflected 
back down and out to the room at lower right 

steps. The telescope loomed in the 
center of the room, shadowy and intri- 
cate, its works mostly exposed, like a 
fine timepiece under a glass bell. The 
telescope. Dr. Greenstein had told me, 
works something like a clock. Its tube 
has to keep time exactly with the move- 
ment of the stars so that a star's light 
can stay riveted to a photographic plate 
for several hours at a stretch. The tele- 
scope, with its reflecting mirror two 
hundred inches in diameter, serves as a 


A Night at the Observatory 

sort of bucket to catch as much light as 
possible from a star and concentrate it 
on film: it could pick up the light of a 
ten-watt bulb a million miles away. The 
purpose of the telescope is not to 
magnify, for no matter how great the 
magnification, no star would ever show 
up as more than a point of light. 

The footsteps I had heard belonged 
to the night assistant for the telescope, 
Gary Tuton, a lean young man with 
short, wavy hair. Tuton is the tech- 
nician who runs the telescope for the 
astronomers. He walked over to a con- 
trol console and pressed a button. The 
telescope sprang into life. The big mir- 
ror, which weighs almost fifteen tons, 
rests at the bottom of the telescope 
tube, an open steel cylinde some sixty 
feet long. The tube swivels north and 
south inside a huge frame called the 
yoke, and the yoke swivels from east to 
west on two enormous bearings, so that 
the tube, with the mirror at its bot- 
tom, can aim at any point in the sky. 


low the yoke spun to the east and 
the tube swiveled to the north, only, 
since both these motions happened 
simultaneously, the movement was one 
smooth undulation. The tube can be 
locked on a star, just as the pencil in 
a compass can be locked at any given 
radius. Then the star can be tracked 
along its path simply by turning the 
yoke, which is fixed on the North Star 
as if it were the dot at the center of a 
circle. The movement of the yoke has 
to be very delicate. Tuton explained 
that the huge bearings at either end of 
the yoke are floated on thin films of oil 
so that the telescope, which weighs five 
hundred tons, can be turned by hand. 
The oil pumps under the enormous 
bearings whined. The observatory 
sounded like a very active railroad 

Slowly and ponderously th€ two- 
hundred-and-twenty-five-ton doors that 
covered the slit in the dome pulled 
aside, revealing a widening band of 
dark blue sky. It was like being inside 
the eye of an awakening animal. "Some- 
times, in winter, when the dome is cov- 

ered with snow, 1 have to go up top 
and sweep the snow off the slit," Tuton 
said. "One night last winter it got so 
cold that the gears on the doors that 
cover the slit in the dome froze. No 
matter what I did, one shutter would 
shut and the other wouldn't, and there 
was a snowstorm coming. But by and 
large the weather is pretty good up 
here. Last year we used the telescope 
on three hundred and ten nights." 

A door banged and Dr. Greenstein 
appeared, struggling under a load of 
lenses and photographic film. Since it 
was still too early to begin taking pic- 
tures. Dr. Greenstein said that he was 
going up into the prime-focus cage at 
the top of the telescope tube and in- 
vited me to come along. "I want to 
take a look at a group of stars, a globu- 
lar cluster called Messier 13," he said. 
"There's a peculiar star in it that I want 
to get a spectrum of later on. It's in 
with such a mass of other stars that I 
want to make sure I get my bearings 

Dr. Greenstein explained that the 
prime focus was the simplest and most 
direct way of looking through the tele- 
scope. There are several different ways, 
and none of them is the conventional 
one, used with binoculars or refractor 
telescopes, of holding the telescope up 
to your eyes. Instead of focusing light 
through a lens, the big mirror bounces 
the light back up the tube and concen- 
trates it at a point fifty-five feet above. 
The exact spot is called the prime focus. 
The astronomer sits in the prime-focus 
cage, which is like a balloonist's bas- 
ket high inside the telescope tube, and 
from this vantage point he can photo- 
graph the image directly. 

"I like it in the prime-focus cage," 
Dr. Greenstein concluded. "You feel 
closer to the stars." Then he frisked 
himself and me, removing any hard ob- 
jects, such as coins and pens, that might 
fall on the mirror and damage it. It had 
taken eleven years to polish the mirror 
into exactly the right configuration; a 
scratch could mean years more polish- 
ing. We climbed to a balcony, boarded 
the dome elevator, and began a long. 

hair-raising ascent as the elevator rose 
upward and outward, following the 
overhanging contour of the dome. 
Through the slit we could see the 
ground several stories below, and sev- 
eral thousand feet below that, the lights 
of the valley floor. The dome elevator 
is a peculiar, unenclosed contraption 
like a long spoon; we stood at the outer 
end of it where the bowl would be. 
After a bumpy ride, the elevator de- 
posits the astronomer, like a dollop of 
medicine, inside the mouth of the tele- 
scope. At this point, the astronomer is 
about seventy feet above the floor of the 
dome, with very little to hang on to. 

"People have gotten killed on tele- 
scopes," Dr. Greenstein said with what 
I thought was poor timing as we lurched 
unevenly up and out. "Sometimes as- 
tronomers get squashed by a telescope 
slewing about, but that doesn't happen 
very often." 

I gripped the railing of the elevator, 
fixed my eyes firmly on the top of the 
dome, and asked Dr. Greenstein to tell 
me more about the peculiar star in 
Messier 13. "Globular clusters, like 
Messier 13, are sort of suburbs of our 
galaxy which contain some of the oldest 
stars, and for this reason they might 
have a bearing on the quasars, which 
are supposed to be primordial objects, 
too," he said. "However, the star I 
want to look at now is blue, a color 
usually associated with younger stars, 
so in this case it must represent a pe- 
culiar stage of evolution. Although this 
star— Barnard 29— is blue, it has a pe- 
culiar energy distribution. Its spectrum 
is too much in the red, and one possi- 
bility I want to check tonight is whether 
it couldn't in fact be a close pair, a 
double star, one blue and one red." 


on we were directly on top of the 
telescope tube, and Dr. Greenstein 
flung open a flimsy gate at the end of 
the elevator platform. The prime-focus 
cage — a bucket perhaps five feet in di- 
ameter and five feet deep — was about 
eighteen inches below us. Dr. Green- 
stein explained that the elevator couldn't 
go all the way to the cage because of 



A Night at the Observatory 

the danger of collision with the tele- 
scope: we would have to travel across 
the remaining gap ourselves. So saying, 
he flung himself into the void and dis- 
appeared into the mouth of the tele- 

Inside the bucket was a chair and an 
empty well that looked straight down 
at the mirror: the astronomer fits his 
instruments into the well. When Tuton 
was sure that we were safely installed, 
and that nothing could drop on the 
mirror, he opened the diaphragm that 
covered it. Slowly, like a water lily, the 
petals of the diaphragm lifted, reveal- 
ing what looked like a pond of rippling, 
shimmering water beneath. The stars, 
which wouldn't stay still, were streak- 
ing like meteors; the mirror, it seemed, 
was popping a few millionths of an 
inch with the change of temperature. 
Tuton slewed the telescope off in search 
of Messier 13 and Barnard 29. As one 
side of the bucket dipped suddenly 
down, the chair, which was on rails, 
moved around and down with gravity, 
so that the astronomer was always up- 
right; the sensation was like riding very 
slowly in a Ferris wheel. Stars shot 
through the big mirror as we sailed 
along. The telescope came to a smooth 
halt, moving just fast enough to keep 
the stars still in spite of the rotation of 
the earth. Dr. Greenstein peered into 
the pool of light for a moment. Then he 
maneuvered a tiny lens that looked 
like a magnifying glass— it was tied to 
the well with a string— until he found 
the exact spot where the image was 
clearest. This was the prime focus. 

"We're right on the beam," Dr. 
Greenstein said, handing the lens to 
me. As 1 looked down, 1 felt my glasses 
begin to slide down my nose; I grabbed 
them just before they dropped down 
the well toward the mirror. The lens re- 
solved the chaotic splotches of dancing 
light, and I saw an enormous rash of 
stars, each one a point of hard, bril- 
liant light. I couldn't make out Bar- 

Dwarfed by the telescope's huge frame, art 
astronomer stands on the mirror casing prior 
to its intallation at the observatory in 1948. 

nard 29. Dr. Greenstein was able to 
converse with Tuton over an intercom, 
and he asked him to slop the telescope's 
tracking drive. No sooner had the tele- 
scope stopped moving than Messier 13 
and Barnard 29 slipped out of the field 
of vision. Other stars whizzed across 
the mirror, following Messier 13 into 
seeming oblivion; a given star crossed 
the mirror in about ten seconds, before 
vanishing. That, Dr. Greenstein said, 
showed how fast the earth, with the 
telescope, was turning. Tuton's voice 
crackled through the microphone, ask- 
ing how I felt. I replied that I was 
getting a little dizzy. Tuton started up 
the tracking device; the telescope passed 
all the stars that had been whipping by. 
and soon we were safely back with 
Messier 13. 

"Did Dr. Greenstein tell you about 
the time I was stuck up there?" Tuton 
asked; and his voice crackled on, "I 
was in the prime-focus cage when the 
power for the telescope shorted out. It 
was a cold winter night. I had to climb 
down, which was the hairiest thing I 
ever did. What made me do it was not 
the cold so much as what the men who 
came in the morning would say. I'd 
never have lived it down." 


Lt last Tuton wafted the telescope 
toward the elevator platform for us to 
board. I fixed my eye on the top of the 
dome again. Dr. Greenstein glanced at 
his watch and said that he wished the 
elevator would hurry, because it was al- 
ready dark enough to start using the 
spectrograph. He shouted down to 
Tuton to start setting up the telescope 
for the coude focus. The coude focus is 
in a room outside the telescope alto- 
gether, and the light from a star is de- 
flected to it by a mirror— called the 
coude flat— which bounces the starlight 
in a thin beam down through a hole in 
the southern foundation of the tele- 
scope and into the coude room one 
floor below, where the spectrographs 
are kept. The film to record the spec- 
trum of a star is in this room, which 
serves something of the purpose of an 
old Brownie box camera. As we reached 

the ground, an electronic engine whirred 
and the coude flat, weighing a ton and 
a half, lifted slowly into position just 
below the prime-focus cage. It glittered 
like a jewel inside a watch 

Dr. Greenstein fetched the films he 
had brought with him and disappeared 
down the steps into the coude room, 
a tiny chamber that descends steeply 
in line with the yoke, pointing at the 
North Star. It was already after eight 
o'clock. Barnard 29 was nestled among 
so many stars that the final zeroing in 
had to be done by dead reckoning. 
"There's a sort of triangle of stars," 
said Dr. Greenstein, who had returned 
to the control room at the top of the 
steps. "See it? There ought to be a 
double star on the upper left. Got it?" 
He sounded like a man finding his way 
with a road map. Tuton said he had it. 
"Do you know what the most difficult 
object to find is?" Tuton asked as he 
turned a knob for fine adjustment; I 
said I didn't. "It's the moon. The moon 
is so close, and it's moving so fast, that 
it's like trying to aim a rifle at a mov- 
ing target close by, instead of at the 
trees standing behind it." 

All of a sudden, Barnard 29 disap- 
peared from view. It was as if the tele- 
scope had gone dead. Tuton raced out 
into the dome and peered up at the sky 
through the slit; a long, wispy cloud 
was obstructing the view. "Looks like 
it's going to-be a cloud-dodging night," 
he said. Quickly Tuton and Greenstein 
flipped the telescope to another star, 
called HD 165195, which was in a 
cloudless part of the sky. 

1 asked Dr. Greenstein whether we 
would see any quasars that night. 
"The moon is up, so we can't work on 
anything as dim as quasars," he said. 
"That's probably just as well. There 
isn't much you can tell by looking at a 
quasar anyway. Instead, I will be doing 
long exposures on some of the oldest 
stars in the galaxy. The procedure is 
much the same as with quasars; and in 
fact part of what we'll be doing is re- 
lated to quasars. There is a theory that 
has to be explored that the quasars are 


a remnant of the first formation of 
galaxies. According to this theory, dur- 
ing the contraction of the gases that 
formed the galaxies, some super-mas- 
sive objects formed within them. These 
objects may have become extremely 
den>e and pulled themselves together 
so rapidly that they exploded. Perhaps 
that is what the quasars are. I don't 
know. I'm fairly neutral on the subject. 
There is evidence in our own galaxy o( 
a superexplosion far greater than the 
explosion of a supernova, but less. I 
think, than a quasar explosion. In any 
event, if the quasars represent monu- 
mental explosions within. galaxies dur- 
ing the half-billion years or so that the 
galaxies and the stars were condensing 
out of primeval gas clouds, then you 
would expect that the oldest stars, the 
first to condense from the gases, would 
be heavily contaminated by the ele- 
ments in the quasars. They would have 
been loaded with the products of 
quasar evolution." 

Dr. Greenstein turned out the lights 
in the control room and pressed a but- 
ton to start the exposure. The control 
room was lit only by the soft-green glow 
of the dials on the control panel, like 
the cockpit of an airplane at night. 
"So 1 will be looking at some of the 
oldest stars in our galaxy, like this one, 
to see whether they have the same ele- 
ments and in roughly the same pro- 
portions, as the quasars. We don't 
know yet the exact composition of the 
quasars, but we may be able to do some- 
thing with oxygen or iron. If they have 
the same elements, it might indicate 
quasars were the raw material in form- 
ing stars. But if there are other elements 
aside from those found in quasars, it 
might prove that the quasars are not 
important in star evolution, for the old- 
est stars don't seem to have manufac- 
tured many new elements after their 
formation, such as metals But if I find 
a trace of metal in HD 165195, I have 
to decide whether it might have been 
cooked within the star after all. or 
whether the metal was part of the orig- 
inal gases of which the star was com- 
posed. The chances are we won't know 

much more after tonight. I'll need this 
type of information on hundreds o( 
stars before I can begin to get any- 

The lime was eight-thirty. I found 
myself standing in the path of the 
slender stream of light from HD 165195. 
and Dr. Greenstein asked me to step 
out of the way, which wasn't easy, since 
the control room was cramped and 
narrow A licking sound filled the room. 
Dr. Greenstein said that the ticking 
came from the photoelectric scaler, 
which counts the number of photons 
coming from a star, like a light meter, 
hach tick meant twenty thousand pho- 
tons of light. A dial kept count of the 
ticks, and Dr. Greenstein said that, for 
this exposure, he wanted about thirty- 
three hundred. 


Le invited me to look through the 
eyepiece of the spectrograph. A spec- 
trograph, an apparatus in the control 
room that intercepted the light coming 
from HD 165195. refracts and spreads 
out the light from a star into its com- 
ponent wave lights, giving a spectrum 
something like the light from a prism. 
The lines in a spectrum show the ele- 
ments in a star. They also show how 
fast an object is receding from the earth 
by how much the lines are shifted to the 
red end of the spectrum. This is called 
the red shift, and it was in this way 
that Schmidt first decided the quasars 
were tremendously distant objects. 
Through the eyepiece, the star ap- 
peared as a fuzzy, bright-green spark; 
the star's light had been shattered by 
passing through a slit and some grat- 
ings inside the spectrograph. Dr. Green- 
stein said the light had left the star 
ten thousand years ago. Tuton darted 
across to the telescope's control panel 
and slowed down the telescope's track- 
ing drive by a tiny fraction. "We want 
to make the star trail along the slit in 
the spectrograph," he said. "This is 
what we have to do with faint objects. 
It's like painting one brush stroke over 
another, until you get the proper in- 
tensity on the plate." 

With everything squared away, Tu- 

ton settled down by the eyepiece, 
stretched, yawned, and tuned in a 
radio to a rock-'n'-roll station in San 
Bernardino. He kept an ear cocked to 
make sure the ticking didn't stop, and 
every once in a while he checked the 
eyepiece to make sure the star was still 
there. I asked Dr. Greenslein why he 
and the other astronomers couldn't 
stay in Pasadena, and phone down to 
Tuton whenever they wanted a plate 
taken of a star. "There are loo many 
things that can go wrong," Dr. Green- 
stein said. "I wouldn't know whether 
a plate was any good or not unless I 
was here." Tuton concurred with him. 
"I've never been trained in astron- 
omy," he said. "I can run the telescope 
all right, and find a star, but when it 
comes to astronomy, I just haven't the 
foggiest idea what's going on. The as- 
tronomer never says what he's doing. 
Half the time he doesn't know what 
he's done until he's gotten back to 
Pasadena. I didn't know anything 
about quasars until I read about them 
in the papers." Then Tuton pulled out 
a magazine, which he squinted at by 
the light of the dials. 

Dr. Greenstein suggested that we go 
out on the catwalk. Except for a gentle 
breeze, the plateau was absolutely still. 
I could see the smaller dome of the 
Schmidt telescope about half a mile to 
the east. Dr. Greenstein pointed out a 
spot between the two domes where an 
Air Force bomber had crashed four 
years earlier, killing the crew and two 
horses that belonged to the superin- 
tendent of the observatory but miracu- 
lously doing no damage to the tele- 
scope. Away to the northwest, the smog 
over Los Angeles glowed- possibly in 
something of the way the outer gases 
of the quasars shine, powered by some 
mysterious force inside. There was a 
light mist on the mountain, and the 
half-moon glowed overhead. "Only 
spectrograph work can be done in full 
moonlight, and even that is terribly 
difficult." Dr. Greenstein said. "You 
have to be very careful that the moon- 
light doesn't contaminate your plate. 
I thought I'd made a great spectro- 


A Night at the Observatory 

graphic discovery once, only to find 
that it was the light of the moon, and 
not of the star. There is a gadget called 
a moon eliminator. I wish we could get 
rid of the moon for good!" 


r. Greenstein glanced at his watch. 
It was eleven o'clock. "The night's 
young yet," he said energetically. He 
went inside, bustled into the control 
room, checked the dial that counted 
the ticks, and shut down the spectro- 
graph. Tuton slewed the telescope to 
another star. BD 39°4926. which Dr. 
Greenstein explained was also very old 
and might shed light on whether qua- 
sars had to do with galaxy formation. 
Then, since the exposure would last for 
three hours. Dr. Greenstein went 

downstairs to his darkroom to develop 
the plate on HD 165195. 

Amid a sloshing of water and the 
acrid odor of hypo Dr. Greenstein 
said, "I don't really believe that the 
older stars are residues of quasars. I 
don't believe the quasars are a part of 
galaxies, and therefore I don't happen 
to believe that they have anything to 
do with star evolution. There is evi- 
dence of giant explosions in galaxies 
now, but whether these caused quasars 
or not, we don't know. But what we 
know of quasars really isn't conducive 
to the formation of stars. I don't be- 
lieve quasars come from explosions, 
though other astronomers do. Specu- 
lation is like the stock market. I feel 
that the quasars instead may be in 

Seated in the prime-focus cage, his hack to 
the sky. an astronomer photographs images 
reflected up Jront the 200-inch mirror 

some kind of balance condition, like a 
star, and that they are isolated objects, 
and that they are formed of matter 
between galaxies. Other people feel 
they are little things which have been 
blown out of galaxies. Another group 
believes that the quasars are extremely 
dense objects and that their red shifts 
are caused by gravity, rather than by 
speed or distance. I don't know. The 
best we can do is to test the different 
theories, which is what I'm trying to do 

Just after midnight. Dr. Greenstein 
came up from the darkroom. He 
checked the star, which was ticking 


away nicely on the slit, and sat on a 
table. "That's all the developing I do 
tonight," he said. "It's too risky when 
you're tired." He had evidently lost 
his second wind. I asked him if he had 
been able to tell anything about HD 
165195, and he said he hadn't. "It's 
too late at night for discoveries," he 
said with a yawn. "There's nothing like 
making a great discovery that you 
might absent-mindedly wipe off the 
plate with a wet finger. I make it a rule 
never to make great discoveries after 

Dr. Greenstein yawned again. I fol- 
lowed him over to a couple of reclin- 
ing chairs by the control console under 
the north bearing. Just visible in the 
starlight, he lay back with his arms 
folded behind his head as a pillow and 
his eyes shut. The moon, for the time 
being, was obscured, so it was unusu- 
ally dark inside the dome. As I became 
more accustomed to the darkness — it 
was much darker than in the control 
room, which contained a number of 
luminous dials — I could make out 
more and more of the telescope. Dr. 
Greenstein opened his eyes. "I could 
look at it forever," he said. "No mat- 
ter how long you look at it, it always 
looks different. It looks different now, 
when you can barely see it in the dim 
starlight, from what it did a few min- 
utes ago in the light of the half-moon. 
It's different from whatever side you 
look at it. Right now, it just sits there 
and broods. It is a remarkable subor- 
dination of brute force for delicate 
ends. All this mechanism is for is to 
move one piece of glass; and all the 
glass is for is to carry one thin layer of 
aluminum that reflects starlight. I wish 
it were quieter! We must get rid of 
those oil pumps." 


it last Dr. Greenstein's voice drifted 
off. He was fast asleep. After a time he 
sat bolt upright and looked at his 
watch. It was two fifteen. Above him, 
the telescope was almost completely on 
its side, as if it, too, had been asleep. 
Over the last three hours, its tracking 
of BD 39°4926 had caused it to as- 

sume this position. The ticking ceased 
abruptly when Dr. Greenstein checked 
the meter and ended the exposure. 
After rummaging around in the inky 
coude room to change plates. Dr. 
Greenstein came back to the control 
room and decided to return to Bar- 
nard 29. "We need about three hours, 
though with this much moon, I doubt 
if we'll get it," he said briskly as he 
zeroed in the telescope. As he was 
talking, the ticking became more and 
more sporadic, slowing down; finally it 
stopped altogether. Tuton, who had 
had no nap, and who looked a little 
scruffy, went out under the dome and 
squinted up through the slit. Barnard 
29 was obscured by clouds again. 
"What do we do now?" Tuton asked 
Greenstein. Tuton said that what he 
would like to do now would be go 
home and go to bed. 

"We're getting only about ten min- 
utes' exposure time to the hour, but as 
long as I can get even that much, I 
can't shut down," Dr. Greenstein said, 
and added unhappily, "the telescope's 
time is more valuable than my own." 
It costs one thousand dollars a night 
to operate the telescope. Suddenly a 
great rift appeared in the clouds, and 
the moon emerged. It was greeted with 
a terrific burst of ticks. Dr. Greenstein 
shouted to Tuton to shut off the spec- 
trograph. "We're belter off wasting 
exposure time and not getting contami- 
nation," Dr. Greenstein grumbled, ex- 
haling a cloud of cigar smoke that 
glowed derisively in the moonlight. It 
was a little after two forty-five, and I 
had the impression that Dr. Greenstein 
was about to call it a night 

At three fifteen the sky cleared and 
Tuton started the exposure once more. 
Since he was stiff and tired. Dr. Green- 
stein suggested another spin around 
the catwalk. There was low-lying mist 
on the plateau, and not far away a jay 
woke up raucously. The air was chill 
and damp. The east was as dark as 
ever, but Dr. Greenstein said he could 
see the zodiacal light, which heralds 
the dawn. "We won't be able to keep 
the exposure going much longer," he 

went on. "The sun is already beginning 
to heat up the atmosphere to the east, 
which makes it bubble a bit." Grog- 
gily. I looked for bubbles in the east, 
but saw none. A flush of pink appeared 
and spread rapidly; the stars to the 
east blinked out, though the ones to 
the west were, for the time being, as 
hard and brilliant as they had been for 
most of the night. Shadows grew where 
none had been before, and we could 
begin to see colors the green of the 
pines, the pink clay of the road. Dr 
Greenstein went back inside and called 
down to Tuton to turn off the exposure 
before it was contaminated. 

Ahe inside of the dome was suffused 
with pink; the dome's interior, too, was 
of brilliant aluminum, and caught the 
dawn through the slit. The telescope 
was visible again, like a dinosaur 
emerging from a misty bog. "This is 
my time on the telescope," Tuton said, 
"the time after dawn, but before all 
the stars are washed out. It's useless 
for spectrography or photography, so I 
just aim the telescope at what I want 
to look at. I think Saturn is in a good 
position for viewing." 

He consulted an astronomy book 
and quickly swung the telescope to a 
new position. He snapped the eyepiece 
into place, focusing it. He stepped 
aside, and I took a look. There was 
Saturn, as big as a football and, with 
its rings forming an oval around it, 
somewhat the same shape. Through 
the two-hundred-inch telescope, Sat- 
urn was so brilliant that it hurt the 
eyes Dr. Greenstein squinted through 
the eyepiece, grunting. "I never par- 
ticularly liked the solar system," he 
said, relinquishing the telescope. I 
looked again; Saturn was less brilliant 
than before, and it was fading fast in 
the sunlight. Soon it vanished alto- 
gether, like the Cheshire cat, leaving 
nothing behind but a patch of pale- 
blue sky. 

Henry S F. Cooper, Jr , a member of 
the editorial staff of l\\z New Yorker. 
writes frequently on scientific subjects. 


Copernicus addresses this preface of his revolutionary 
book on the solar system to Pope Paul III. 

4 Preface to De Revolutionibus 

Nicolaus Copernicus 

From Occasional Notes to the Royal Astronomical Society, No. 10, 1947. 



I may well presume, most Holy Father, that certain people, as soon 
as they hear that in this book On the Revolutions of the Spheres of the Universe 
I ascribe movement to the earthly globe, will cry out that, holding such 
views, I should at once be hissed off the stage. For I am not so pleased 
with my own work that I should fail duly to weigh the judgment which 
others may pass thereon; and though I know that the speculations of a 
philosopher are far removed from the judgment of the multitude — for his 
aim is to seek truth in all things as far as God has permitted human reason 
so to do — yet I hold that opinions which are quite erroneous should be 

Thinking therefore within myself that to ascribe movement to the 
Earth must indeed seem an absurd performance on my part to those who 
know that many centuries have consented to the establishment of the 
contrary judgment, namely that the Earth is placed immovably as the 
central point in the middle of the Universe, I hesitated long whether, 
on the one hand, I should give to the light these my Commentaries written 
to prove the Earth's motion, or whether, on the other hand, it were better 
to follow the example of the Pythagoreans and others who were wont 
to impart their philosophic mysteries only to intimates and friends, and 
then not in writing but by word of mouth, as the letter of Lysis to Hipparchus 
witnesses. In my judgment they did so not, as some would have it, through 
jealousy of sharing their doctrines, but as fearing lest these so noble and 
hardly won discoveries of the learned should be despised by such as either 
care not to study aught save for gain, or — if by the encouragement and 
example of others they are stimulated to philosophic liberal pursuits — 
yet by reason of the dulness of their wits are in the company of philosophers 
as drones among bees. Reflecting thus, the thought of the scorn which 
I had to fear on account of the novelty and incongruity of my theory, well- 
nigh induced me to abandon my project. 

These misgivings and actual protests have been overcome by my friends. 
First among these was Nicolaus Schonberg, Cardinal of Capua, a man 


renowned in every department of learning. Next was one who loved me 
well, Tiedemann Giese, Bishop of Kulm, a devoted student of sacred and 
all other good literature, who often urged and even importuned me to 
publish this work which I had kept in store not for nine years only, but 
to a fourth period of nine years. The same request was made to me by 
many other eminent and learned men. They urged that I should not, 
on account of my fears, refuse any longer to contribute the fruits of my 
labours to the common advantage of those interested in mathematics. 
They insisted that, though my theory of the Earth's movement might 
at first seem strange, yet it would appear admirable and acceptable when 
the publication of my elucidatory comments should dispel the mists of 
paradox. Yielding then to their persuasion I at last permitted my friends 
to publish that work which they have so long demanded. 

That I allow the publication of these my studies may surprise your 
Holiness the less in that, having been at such travail to attain them, I had 
already not scrupled to commit to writing my thoughts upon the motion 
of the Earth. How I came to dare to conceive such motion of the Earth, 
contrary to the received opinion of the Mathematicians and indeed contrary 
to the impression of the senses, is what your Holiness will rather expect 
to hear. So I should like your Holiness to know that I was induced to 
think of a method of computing the motions of the spheres by nothing 
else than the knowledge that the Mathematicians are inconsistent in these 

For, first, the mathematicians are so unsure of the movements of the 
Sun and Moon that they cannot even explain or observe the constant 
length of the seasonal year. Secondly, in determining the motions of 
these and of the other five planets, they do not even use the same principles 
and hypotheses as in their proofs of seeming revolutions and motions. 
So some use only concentric circles, while others eccentrics and epicycles. 
Yet even by these means they do not completely attain their ends. Those 
who have relied on concentrics, though they have proven that some different 
motions can be compounded therefrom, have not thereby been able fully 
to establish a system which agrees with the phenomena. Those again 
who have devised eccentric systems, though they appear to have well-nigh 
established the seeming motions by calculations agreeable to their 
assumptions, have yet made many admissions which seem to violate the 
first principle of uniformity in motion. Nor have they been able thereby 
to discern or deduce the principal thing — namely the shape of the Universe 
and the unchangeable symmetry of its parts. With them it is as though 
an artist were to gather the hands, feet, head and other members for his 
images from divers models, each part excellently drawn, but not related 
to a single body, and since they in no way match each other, the result 
would be monster rather than man. So in the course of their exposition, 
which the mathematicians call their system (fiedoSos) we find that they 
have either omitted some indispensable detail or introduced something 
foreign and wholly irrelevant. This would of a surety not have been so 
had they followed fixed principles; for if their hypotheses were not 
misleading, all inferences based thereon might be surely verified. Though 
my present assertions are obscure, they will be made clear in due course. 

I pondered long upon this uncertainty of mathematical tradition in 
establishing the motions of the system of the spheres. At last I began to 


Preface to De Revolutionibus 

chafe that philosophers could by no means agree on any one certain theory 
of the mechanism of the Universe, wrought for us by a supremely good 
and orderly Creator, though in other respects they investigated with 
meticulous care the minutest points relating to its orbits. I therefore 
took pains to read again the works of all the philosophers on whom I could 
lay hand to seek out whether any of them had ever supposed that the 
motions of the spheres were other than those demanded by the mathematical 
schools. I found first in Cicero that Hicetas * had realized that the Earth 
moved. Afterwards I found in Plutarch that certain others had held 
the like opinion. I think fit here to add Plutarch's own words, to make 
them accessible to all : — 

"The rest hold the Earth to be stationary, but Philolaus the 
Pythagorean says that she moves around the (central) fire on an 
oblique circle like the Sun and Moon. Heraclides of Pontus and 
Ecphantus the Pythagorean also make the Earth to move, not indeed 
through space but by rotating round her own centre as a wheel on an 
axle t from West to East." 

Taking advantage of this I too began to think of the mobility of the 
Earth; and though the opinion seemed absurd, yet knowing now that 
others before me had been granted freedom to imagine such circles as they 
chose to explain the phenomena of the stars, I considered that I also might 
easily be allowed to try whether, by assuming some motion of the Earth, 
sounder explanations than theirs for the revolution of the celestial spheres 
might so be discovered. 

Thus assuming motions, which in my work I ascribe to the Earth, 
by long and frequent observations I have at last discovered that, if the 
motions of the rest of the planets be brought into relation with the 
circulation of the Earth and be reckoned in proportion to the orbit of each 
planet, not only do their phenomena presently ensue, but the orders and 
magnitudes of all stars and spheres, nay the heavens themselves, become 
so bound together that nothing in any part thereof could be moved from 
its place without producing confusion of all the other parts and of the 
Universe as a whole. 

In the course of the work the order which I have pursued is as here 
follows. In the first book I describe all positions of the spheres together 
with such movements as I ascribe to Earth; so that this book contains, 
as it were, the general system of the Universe. Afterwards, in the remaining 
books, I relate the motions of the other planets and all the spheres to the 
mobility of Earth, that we may gather thereby how far the motions and 
appearances of the rest of the planets and spheres may be preserved, if 
related to the motions of the Earth. 

I doubt not that gifted and learned mathematicians will agree with 
me if they are willing to comprehend and appreciate, not superficially 
but thoroughly, according to the demands of this science, such reasoning 
as I bring to bear in support of my judgment. But that learned and 
unlearned alike may see that I shrink not from any man's criticism, 

* C. writes Nicetas here, as always, 
t Reading 'evTilortopeyrir. 


it is to your Holiness rather than anyone else that I have chosen to dedicate 
these studies of mine, since in this remote corner of Earth in which I live 
you are regarded as the most eminent by virtue alike of the dignity of your 
Office and of your love of letters and science. You by your influence 
and judgment can readily hold the slanderers from biting, though the 
proverb hath it that there is no remedy against a sycophant's tooth. It may 
fall out, too, that idle babblers, ignorant of mathematics, may claim a right 
to pronounce a judgment on my work, by reason of a certain passage of 
Scripture basely twisted to suit their purpose. Should any such venture 
to criticize and carp at my project, I make no account of them ; I consider 
their judgment rash, and utterly despise it. I well know that even 
Lactantius, a writer in other ways distinguished but in no sense a mathe- 
matician, discourses in a most childish fashion touching the shape of the 
Earth, ridiculing even those who have stated the Earth to be a sphere. 
Thus my supporters need not be amazed if some people of like sort ridicule 
me too. 

Mathematics are for mathematicians, and they, if I be not wholly 
deceived, will hold that these my labours contribute somewhat even to 
the Commonwealth of the Church, of which your Holiness is now Prince. 
For not long since, under Leo X, the question of correcting the ecclesiastical 
calendar was debated in the Council of the Lateran. It was left undecided 
for the sole cause that the lengths of the years and months and the motions 
of the Sun and Moon were not held to have been yet determined with 
sufficient exactness. From that time on I have given thought to their 
more accurate observation, by the advice of that eminent man Paul, 
Lord Bishop of Sempronia, sometime in charge of that business of the 
calendar. What results I have achieved therein, I leave to the judgment 
of learned mathematicians and of your Holiness in particular. And now, 
not to seem to promise your Holiness more than I can perform with regard 
to the usefulness of the work, I pass to my appointed task. 


The introduction to Galileo's Starry Messenger not only 
summarizes his discoveries, but also conveys Galileo's 
excitement about the new use of the telescope for as- 
tronomical purposes. 

The Starry Messenger 

Galileo Galilei 

An excerpt from Discoveries and Opinions of Galileo 
translated by Stillman Drake, 1957. 


Which contains and explains recent observations 

made with the aid of a new spyglass 3 

concerning the surface of the moon, 

the Milky Way, nebulous stars, and 

innumerable fixed stars, 

as well as four planets never before seen, and 

now named 

The Medicean Stars 

Great indeed are the things which in this brief treatise I 
propose for observation and consideration by all students of 
nature. I say great, because of the excellence of the subject 
itself, the entirely unexpected and novel character of these 
things, and finally because of the instrument by means of 
which they have been revealed to our senses. 

Surely it is a great thing to increase the numerous host 
of fixed stars previously visible to the unaided vision, adding 
countless more which have never before been seen, exposing 
these plainly to the eye in numbers ten times exceeding the 
old and familiar stars. 

It is a very beautiful thing, and most gratifying to the 
sight, to behold the body of the moon, distant from us al- 
most sixty earthly radii, 4 as if it were no farther away than 

3 The word "telescope" was not coined until 1611. A detailed 
account of its origin is given by Edward Rosen in The Naming 
of the Telescope (New York, 1947). In the present translation 
the modern term has been introduced for the sake of dignity 
and ease of reading, but only after the passage in which Galileo 
describes the circumstances which led him to construct the in- 
strument (pp. 28-29). 

4 The original text reads "diameters" here and in another 
place. That this error was Galileo's and not the printer's has 
been convincingly shown by Edward Rosen (/sis, 1952, pp. 


two such measures— so that its diameter appears almost 
thirty times larger, its surface nearly nine hundred times, 
and its volume twenty-seven thousand times as large as 
when viewed with the naked eye. In this way one may learn 
with all the certainty of sense evidence that the moon is 
not robed in a smooth and polished surface but is in fact 
rough and uneven, covered everywhere, just like the earth's 
surface, with huge prominences, deep valleys, and chasms. 
Again, it seems to me a matter of no small importance to 
have ended the dispute about the Milky Way by making 
its nature manifest to the very senses as well as to the 
intellect. Similarly it will be a pleasant and elegant thing to 
demonstrate that the nature of those stars which astrono- 
mers have previously called "nebulous" is far different from 
what has been believed hitherto. But what surpasses all 
wonders by far, and what particularly moves us to seek the 
attention of all astronomers and philosophers, is the discov- 
ery of four wandering stars not known or observed by any 
man before us. Like Venus and Mercury, which have their 
own periods about the sun, these have theirs about a cer- 
tain star that is conspicuous among those already known, 
which they sometimes precede and sometimes follow, with- 
out ever departing from it beyond certain limits. All these 
facts were discovered and observed by me not many days 
ago with the aid of a spyglass which I devised, after first 
being illuminated by divine grace. Perhaps other things, 
still more remarkable, will in time be discovered by me or 
by other observers with the aid of such an instrument, the 
form and construction of which I shall first briefly explain, 
as well as the occasion of its having been devised. After- 
wards I shall relate the story of the observations I have 

344 ff . ) . The slip was a curious one, as astronomers of all schools 
had long agreed that the maximum distance of the moon was 
approximately sixty terrestrial radii. Still more curious is the 
fact that neither Kepler nor any other correspondent appears to 
have called Galileo s attention to this error; not even a friend 
who ventured to criticize the calculations in this very passage. 


The end of this summary of Kepler's work in mechanics 
shows how seriously Kepler took the idea of the harmony 
of the spheres. 

6 Kepler's Celestial Music 

Bernard Cohen 

An excerpt from his book The Birth of a New Physics, 1960. 

Since Greek times scientists have insisted that Nature is 
simple. A familiar maxim of Aristotle is. "Nature does 
nothing in vain, nothing superfluous. " Another expres- 
sion of this philosophy has come down to us from a 
fourteenth-century English monk and scholar, William 
of Occam. Known as his "law of parsimony" or "Oc- 
cam's razor" (perhaps for its ruthless cutting away of 
the superfluous), it maintains, "Entities are not to be 
multiplied without necessity." "It is vain to do with more 
what can be done with fewer" perhaps sums up this 

We have seen Galileo assume a principle of simplicity 
in his approach to the problem of accelerated motion, 
and the literature of modern physical science suggests 
countless other examples. Indeed, present-day physics is 
in distress, or at least in an uneasy state, because the 
recently discovered nuclear "fundamental particles" ex- 
hibit a stubborn disinclination to recognize simple laws. 
Only a few decades ago physicists complacently assumed 
that the proton and the electron were the only "funda- 
mental particles" they needed to explain the atom. But 
now one "fundamental particle" after another has crept 
into the ranks until it appears that there may be as many 
of them as there are chemical elements. Confronted with 
this bewildering array, the average physicist is tempted 


to echo Alfonso the Wise and bemoan the fact that he 
was not consulted first. 

Anyone who examines Fig. 14 on page 58 will see at 

Fig. 22. The ellipse, drawn in the manner shown in 
(A), can have all the shapes shown in (B) if you use 
the same string but vary the distance between the pins, 
as at F 2 , F 8> F 4 , etc. 


Kepler's Celestial Music 

Fig. 14. The Ptolemaic system (A) and the Copernican 
system (B) were of about equal complexity, as can be 


once that neither the Ptolemaic nor Copernican system 
was, in any sense of the word, "simple." Today we know 
why these systems lacked simplicity: restricting celes- 
tial motion to the circle introduced many otherwise 
unnecessary curves and centers of motion. If astrono- 
mers had used some other curves, notably the ellipse, a 
smaller number of them would have done the job better. 
It was one of Kepler's great contributions that he stum- 
bled upon this truth. 

Tlie Ellipse and the Keplerian Universe 

The ellipse enables us to center the solar system on ihe 
true sun rather than some "mean sun" or the center of 
the earth's orbit as Copernicus did. Thus the Keplerian 
system displays a universe of siars fixed in space, a 
fixed sun, and a single ellipse for the orbit ol each 
planet, with an additional one for the moon. In actual 
fact, most of these ellipses, except for Mercury's orbit, 
look so much like circles that at first glance the Kep- 
lerian system seems to be the simplified Copernican 
system shown on page 58 of Chapter 3: one circle for 
each planet as it moves around the sun, and another for 
the moon. 

An ellipse (Fig. 22) is not as "simple" a curve as a 
circle, as will be seen. To draw an ellipse (Fig. 22A), 
stick two pins or thumbtacks into a board, and to them 
tie the ends of a piece of thread. Now draw the curve by 
moving a pencil within the loop of thread so that the 
thread always remains taut. From the method of drawing 
the ellipse, the following defining condition is apparent: 
every point P on the ellipse has the property that the sum 
of the distances from it to two other points F 2 and F t , 
known as the foci, is constant. (The sum is equal to the 
length of the string.) For any pair of foci, the chosen 
length of the string determines the size and shape of the 
ellipse, which may also be varied by using one string- 


Kepler's Celestial Music 

length and placing the pins near to, or far from, one 
another. Thus an ellipse may have a shape (Fig. 22B) 
with more or less the proportions of an egg, a cigar, or 
a needle, or may be almost round and like a circle. But 
unlike the true egg, cigar, or needle, the ellipse must al- 
ways be symmetrical (Fig. 23) with respect to the axes, 

Minor axis 

Fig. 23. The ellipse is always symmetrical with respect 
to its major and minor axes. 

one of which (the major axis) is a line drawn across the 
ellipse through the foci and the other (the minor axis) 
a line drawn across the ellipse along the perpendicular 
bisector of the major axis. If the two foci are allowed to 
coincide, the ellipse becomes a circle; another way of 
saying this is that the circle is a "degenerate" form of an 

The properties of the ellipse were described in an- 
tiquity by Apollonius of Perga, the Greek geometer who 
inaugurated the scheme of epicycles used in Ptolemaic 
astronomy. Apollonius showed that the ellipse, the 
parabola (the path of a projectile according to Galilean 
mechanics), the circle, and another curve called the 
hyperbola may be formed (Fig. 24) by passing planes 
at different inclinations through a right cone, or a cone 
of revolution. But until the time of Kepler and Galileo, 
no one had ever shown that the conic sections occur in 
natural phenomena, notably in the phenomena of mo- 



Fig. 24. The conic sections are obtained by cutting a 
cone in ways shown. Note that the circle is cut parallel 
to the base of the cone, the parabola parallel to one 

In this work we shall not discuss the stages whereby 
Johannes Kepler came to make his discoveries. Not that 
the subject is devoid of interest. Far from it! But at pres- 
ent we are concerned with the rise of a new physics, as 
it was related to the writings of antiquity, the Middle 
Ages, the Renaissance and the seventeenth century. Aris- 
totle's books were read widely, and so were the writings 
of Galileo and Newton. Men studied Ptolemy's Alma- 
gest and Copernicus's De revolutionibus carefully. But 
Kepler's writings were not so generally read. Newton, for 
example, knew the works of Galileo but he probably did 
not read Kepler's books. He may even have acquired 
his knowledge of Kepler's laws at secondhand, very 
likely from Seth Ward's textbook on astronomy. Even 


Kepler's Celestial Music 

today there is no major work of Kepler available in a 
complete English, French, or Italian translation! 

This neglect of Kepler's texts is not hard to under- 
stand. The language and style were of unimaginable 
difficulty and prolixity, which, in contrast with the clarity 
and vigor of Galileo's every word, seemetl formidable 
beyond endurance. This is to be expected, for writing 
reflects the personality of the author. Kepler was a tor- 
tured mystic, who stumbled onto his great discoveries in 
a weird groping that has led his most recent biographer,* 
to call him a "sleepwalker." Trying to prove one thing, 
he discovered another, and in his calculations he made 
error after error that canceled each other out. He was 
utterly unlike Galileo and Newton; never could their 
purposeful quests for truth conceivably merit the descrip- 
tion of sleepwalking. Kepler, who wrote sketches of 
himself in the third person, said that he became a 
Copernican as a student and that "There were three 
things in particular, namely, the number, distances and 
motions of the heavenly bodies, as to which I [Kep- 
ler] searched zealously for reasons why they were as they 
were and not otherwise." About the sun-centered sys- 
tem of Copernicus, Kepler at another time wrote: "I cer- 
tainly know that I owe it this duty: that since I have 
attested it as true in my deepest soul, and since I con- 
template its beauty with incredible and ravishing delight, 
I should also publicly defend it to my readers with all 
the force at my command." But it was not enough to de- 
fend the system; he set out to devote his whole life to 
finding a law or set of laws that would show how the 
system held together, why the planets had the particular 
orbits in which they are found, and why they move as 
they do. 

The first installment in this program, published in 
1596, when Kepler was twenty-five years old, was en- 

* Arthur Koestler, The Sleepwalkers, Hutchinson & Co., Lon- 
don, 1959. 


titled Forerunner of the Dissertations on the Universe, 
containing the Mystery of the Universe. In this book 
Kepler announced what he considered a great discovery 
concerning the distances of the planets from the sun. 
This discovery shows us how rooted Kepler was in the 
Platonic-Pythagorean tradition, how he sought to find 
regularities in nature associated with the regularities of 
mathematics. The Greek geometers had discovered that 
there are five "regular solids," which are shown in Fig. 
25. In the Copernican system there are six planets: 






Fig. 25. The "regular" polyhedra. Tetrahedron has 
four faces, each an equilateral triangle. The cube has 
six faces, each a square. The octahedron has eight 
faces, each an equilateral triangle. Each of the dodec- 
ahedron's twelve faces is an equilateral pentagon. The 
twenty faces of the icosahedron are all equilateral 

Mercury, Venus, Earth, Mars, Jupiter, Saturn. Hence it 
occurred to Kepler that five regular solids might separate 
six planetary orbits. 

He started with the simplest of these solids, the cube. 


Kepler's Celestial Music 

A cube can be circumscribed by one and only one 
sphere, just as one and only one sphere can be inscribed 
in a cube. Hence we may have a cube that is circum- 
scribed by sphere No. 1 and contains sphere No. 2. This 
sphere No. 2 just contains the next regular solid, the 
tetrahedron, which in turn contains sphere No. 3. This 
sphere No. 3 contains the dodecahedron, which in turn 
contains sphere No. 4. Now it happens that in this 
scheme the radii of the successive spheres are in more or 
less the same proportion as the mean distances of the 
planets in the Copernican system except for Jupiter— 
which isn't surprising, said Kepler, considering how far 
Jupiter is from the sun. The first Keplerian scheme (Fig. 
26), then, was this: 

Sphere of Saturn 


Sphere of Jupiter 


Sphere of Mars 


Sphere of Earth 


Sphere of Venus 


Sphere of Mercury. 

"I undertake," he said, "to prove that God, in creating 
the universe and regulating the order of the cosmos, had 
in view the five regular bodies of geometry as known 
since the days of Pythagoras and Plato, and that He has 
fixed, according to those dimensions, the number of 
heavens, their proportions, and the relations of their 
movements." Even though this book fell short of un- 
qualified success, it established Kepler's reputation as a 
clever mathematician and as a man who really knew 
something about astronomy. On the basis of this per- 
formance, Tycho Brahe offered him a job. 


Fig. 26. Kepler's model of the universe. This weird 
contraption, consisting of the five regular solids fitted 
together, was dearer to his heart than the three laws on 
which his fame rests. From Christophorus Leibfried 


Kepler's Celestial Music 

The Keplerian Achievement 

Galileo particularly disliked the idea that solar ema- 
nations or mysterious forces acting at-a-distance could 
affect the earth or any part of the earth. He not only 
rejected Kepler's suggestion that the sun might be the 
origin of an attractive force moving the earth and planets 
(on which the first two laws of Kepler were based), but 
he especially rejected Kepler's suggestion that a lu- 
nar force or emanation might cause the tides. Thus he 

"But among all the great men who have philoso- 
phized about this remarkable effect, I am more as- 
tonished at Kepler than at any other. Despite his open 
and acute mind, and though he has at his fingertips 
the motions attributed to the earth, he has neverthe- 
less lent his ear and his assent to the moon's dominion 
over the waters, and to occult properties, and to such 

As to the harmonic law, or third law, we may ask 
with the voice of Galileo and his contemporaries, Is this 
science or numerology? Kepler already had committed 
himself in print to the belief that the telescope should re- 
veal not only the four satellites of Jupiter discovered by 
Galileo, but two of Mars and eight of Saturn. The reason 
for these particular numbers was that then the number of 
satellites per planet would increase according to a regular 
geometric sequence: 1 (for the earth), 2 (for Mars), 
4 (for Jupiter), 8 (for Saturn). Was not Kepler's 
distance-period relation something of the same pure 
number-juggling rather than true science? And was not 
evidence for the generally nonscientific aspect of Kep- 
ler's whole book to be found in the way he tried to fit 
the numerical aspects of the planets' motions and loca- 
tions into the questions posed in the table of contents 
for Book Five of his Harmony of the World? 


"1. Concerning the five regular solid figures. 

2. On the kinship between them and the harmonic 

3. Summary of astronomical doctrine necessary for 
speculation into the celestial harmonies. 

4. In what things pertaining to the planetary move- 
ments the simple consonances have been ex- 
pressed and that all those consonances which are 
present in song are found in the heavens. 

5. That the clefs of the musical scale, or pitches of 
the system, and the genera of consonances, the 
major and the minor, are expressed in certain 

6. That the single musical Tones or Modes are 
somehow expressed by the single planets. 

7. That the counterpoints or universal harmonies of 
all the planets can exist and be different from one 

8. That the four kinds of voice are expressed in the 
planets; soprano, contralto, tenor, and bass. 

9. Demonstration that in order to secure this har- 
monic arrangement, those very planetary eccen- 
tricities which any planet has as its own, and no 
others, had to be set up. 

10. Epilogue concerning the sun, by way of very 
fertile conjectures." 

Below are shown the "tunes" played by the planets in the 
Keplerian scheme. 


P^w* M| " 

Saturn Jupiter 


>f -gj T #g£l!fff fT 

Earth Venus Mercury 

Fig. 29. Kepler's music of the planets, from his book 
Harmony of the World. Small wonder a man of Ga- 
lileo's stamp never bothered to read it! 


Kepler's Celestial Music 
Surely a man of Galileo's stamp would find it hard to 
consider such a book a serious contribution to celestial 

Kepler's last major book was an Epitome of Coperni- 
can Astronomy, completed for publication nine years 
before his death in 1630. In it he defended his depar- 
tures from the original Copernican system. But what is 
of the most interest to us is that in this book, as in the 
Harmony of the World (1619), Kepler again proudly 
presented his earliest discovery concerning the five regu- 
lar solids and the six planets. It was, he still maintained, 
the reason for the number of planets being six. 

It must have been almost as much work to disentangle 
the three laws of Kepler from the rest of his writings as 
to remake the discoveries. Kepler deserves credit for 
having been the first scientist to recognize that the Co- 
pernican concept of the earth as a planet and Galileo's 
discoveries demanded that there be one physics— apply- 
ing equally to the celestial objects and ordinary terres- 
trial bodies. But, alas, Kepler remained so enmeshed in 
Aristotelian physics that when he attempted to project 
a terrestrial physics into the heavens, the basis still came 
from Aristotle. Thus the major aim of Keplerian physics 
remained unachieved, and the first workable physics for 
heaven and earth derived not from Kepler but from 
Galileo and attained its form under the magistral guid- 
ance of Isaac Newton. 


This brief sketch of Johannes Kepler's life and work 
was initially written as a review of Max Caspar's de- 
finitive biography of Kepler. 

7 Kepler 

Gerald Holton 

An article from the Scientific American, 1960. 

The early part of the 17th century was the hinge 
on which the world view of the West, which had 
been dominated by scholasticism, turned toward 
science. In this period of transition the center of gravity 
of intellectual life shifted from the Scriptures to the 
Book of Nature. The stage for the later triumph of 
Newtonianism was being prepared by men working on 
problems that sprawled across the then indistinctly 
separated disciplines of mathematics, physics, astron- 
omy, cosmology, philosophy and theology. It was, in 
short, the time of Kepler, Galileo and Descartes. 

Of the three Johannes Kepler is perhaps the most 
interesting, both as a scientist and as a personality. He 
is also the least known. Until now there has been no 
serious biography of him in English. This neglect has 
at last been remedied: The definitive biography by 
Max Caspar has been translated from the German by 
C. Doris Hellman of the Pratt Institute in New York. 

As Caspar warns the reader, "No one who has once 
entered the magic sphere that surrounds [Kepler] can 
ever escape from it." Caspar devoted his whole life to 
Kepler; at the time of Caspar's recent death his monu- 
mental 13-volume edition of Kepler's collected works, 
his translation of Kepler's letters and his biography had 
already become a gold mine for scholars— and for pop- 
ular writers. The more meritorious passages of Arthur 
Koestler's The Sleepwalkers, for example, are little 
more than a paraphrase of Caspar. 

Albert Einstein, who felt a deep kinship with Kepler 
(and who, like Kepler, was born in Swabia), said of 
him: "He belonged to those few who cannot do other- 
wise than openly acknowledge their convictions on 
every subject." Caspar's dedication and erudition con- 
sequently found an enormous amount of material on 
which to feed. This book is not merely a detailed por- 
trait of Kepler. It is also an account of the intellectual 
ferment from which modern science arose, and of the 
historical context: the tragic and turbulent age of the 
Counter Reformation and the Thirty Years' War. 

From the beginning Kepler's personal life was unfor- 
tunate. His father Heinrich, as characterized by Kepler 
himself, was an immoral, rough and cpjarrelsome sol- 
dier; his mother Katharina. a querulous and unpleasant 
woman, did not waste much love on her son. Too weak 
and sickly for agricultural labor, (lie hov was sent 
through a school system leading to theological studies 
at the Protestant seminary in Tubingen. One of his 

teachers, Michael Maestlin, introduced him privatelv 
to the Copernican system, which Maestlin was prohib- 
ited from teaching in his public lectures. This was the 
spark that set the youthful mind afire. 

At the age of 23, a few months before attaining the 
goal of his studies (the pulpit), Kepler was directed by 
his seminary to leave in order to serve as teacher of 
mathematics and astronomy at the seminary in Graz. 
He was a wretched teacher, and he had few students. 
This enabled him, however, to devote that much more 
time to other work. Although he spurned astrology as 
it was then practiced, he began to write horoscopes 
and prognostications. He had good reasons to do so: 
It was part of his official duties as district mathemati- 
cian and calendar-maker; he believed that he could 
"separate some precious stones from the dung"; he was 
convinced that the harmonious arrangement of planets 
and stars could impart special qualities to the soul; he 
loved to spread his opinions among the noblemen and 
prelates who read these writings; he needed the money; 
and, last but not least, he found that his predictions 
were often accurate. 

At this time he also began a work that combined a 
little of each of his previous studies: of Plato, Aristotle, 
Euclid, Augustine, Copernicus, Nicholas of Cusa and 
Luther. This was not merely astronomy; his aim was 
nothing less than to discover the plan of the Creator, 
"to think the thoughts of God over again," and to show 
that His plan was Copernican. In 1597 Kepler pub- 
lished the Mysterium Cosmographicum, in which he 
hoped to show the reasons for the number of planets, 
the size of their orbits and their specific motions. His 
method was to search for geometrical regularities with 
which to "explain" physical observation. His immense 
ingenuity, coupled with his unparalleled persistence, 
enabled him to uncover geometrical coincidences which 
satisfied him that his prejudices were correct. The key 
was his famous discovery that the relative radii of the 

Elanetary orbits in the heliocentric system correspond 
lirly well to the relative radii of thin spherical shells 
that may be thought to separate a nested arrangement 
of the five Platonic solids. (The agreement is surpris- 
ingly good; the discrepancy between the radii of the 
shells and those of the orbits according to Copernicus 
was within about 5 per cent, except for the single case 
of Jnpiter— "at which,*' Kepler said, "nobody will won- 
der, considering the great distance.") 



Kepler soon saw that this was an incomplete effort 
at best, and changed his method of work. Still, the 
fundamental motivation behind the Mysterium Cosmo- 
graphicum, namely the search for harmonies, remained 
strong throughout the remaining 33 years of his life. 
In 1597 he could feel the elation of the young man 
who, in Max Weber's phrase, "finds and obeys the 
demon who holds the fibers of his very life." 

But in that same year the dark clouds that seemed 
always to hover over him sent down some lightning 
bolts. He married a young widow whom he described 
later as "simple-minded and fat, confused and per- 
plexed." In 1600, the Counter Reformation having be- 
gun in earnest, all Protestants who did not choose to 
abandon their faith were banished from Graz. Kepler 
found an uncertain refuge in Prague with the aging 
and difficult Tycho Brahe, the foremost astronomer of 
his time, himself in exile from Denmark at the court 
of Emperor Rudolph. 

Brahe lived for only one more year. When he died, 
however, he left Kepler two great treasures: a healthy 
respect for accurate measurement, and a set of the 
best observations of planetary positions that had ever 
been made. Out of this raw material came Kepler's 
second great work, the Astronomia Nova, famous be- 
cause it contained his first two laws of planetary mo- 
tion. During this period Kepler also did fundamental 
work in optics. 

In 1612 he was obliged to leave Prague. His protec- 
tor, the Emperor, had been forced to abdicate; Bohe- 
mia had been devastated by warfare among the con- 
tenders for the throne; his wife had died of a disease 
sweeping the capital. Kepler fled to Linz, where for 
14 years he worked as a schoolteacher and district 
mathematician. At first this was the most tranquil time 
of his life. He brought out his Epitome, an account of 
the Copernican system which was more persuasive 
than Galileo's, but which was neglected by contempo- 
rary scholars, including Galileo. He chose a new wife 
in a comically careful way from 11 candidates (the 
choice turned out rather well), and fought in his Lu- 
theran congregation for the right to interpret the con- 
cept of transubstantiation as he saw fit ( he was deeply 
hurt when, as a result, his pastor excluded him from 

This was also the time when Kepler's aged and 
feeble-minded mother was tried as a witch. It was a 
miserable affair, involving the full spectrum of human 
fears and stupidities. Kepler devoted a full year to her 
defense. He did not claim that witches did not exist, 
but only that his mother was not one. He barely man- 
aged to keep her from the rack and gallows. When one 
of his children died, he turned for solace to his work 
on the Harmonice Mundi, which contained his third 
law of planetary motion and was his last major book. 
He wrote: "I set the Tables [the Rudolphine tables] 
aside, since they require peace, and turned my mind 
to the contemplation of the Harmony." 

Kepler discovered the third law in May, 1618; the 
month also marked the beginning of the Thirty Years' 
War, which devastated Germany. Within a year the 
published part of his Epitome was placed on the Index 

of forbidden books. By 1626 his stay in Linz had be- 
come intolerable; his library had been sealed up by 
the Counter Reformation Commission; the countryside 
was swept by bloody peasant uprisings; the city of Linz 
was besieged; the press that had been printing the 
Rudolphine tables had gone up in flames. It seemed 
that he had no place to go. He was received splendidly 
in Prague by Emperor Ferdinand II, but he refused 
employment at the court because he would have had 
to embrace Catholicism. For a time he found refuge 
in the retinue of the Austrian duke Wallenstein, partly 
because of Wallenstein's interest in astrology. Then in 
1630, as he was passing through Regensburg on a fruit- 
less journey to collect some money that was owed him, 
he was seized by a fever and died. Soon afterward the 
churchyard in which he was buried was destroyed by 
one of the battles of the time. Caspar writes: "It is as 
though the fate which in life gave him no peace con- 
tinued to pursue him even after death." 

But Kepler had left something more durable than a 
headstone: the three laws of planetary motion. During 
his lifetime they attracted little attention. For a gener- 
ation they slept quietly; then they awoke as the key 
inspiration for Newton's theory of universal gravitation. 

These three empirical rules for which Kepler is re- 
membered are scattered through his voluminous work. 
The)' are almost submerged in a flood of other ideas: 
from a means of calculating the optimum size for wine 
casks to an attempt to fix the year of Christ's birth, 
from an excellent discussion of lens optics to an at- 
tempt to connect the position of planets with the local 
weather. (For 20 years Kepler faithfully made weather 
observations for this purpose; and at the end he bravely 
confessed that no connection was provable.) 

His whole work is characterized by this search for 
an arena of fruitful study in disciplines that, from our 
point of view, are incongruously mixed: physics and 
metaphysics, astronomy and astrology, geometry and 
theology, mathematics and music. But this was the 
time when the sciences were emerging from the matrix 
of general intellectual activity and assuming more 
specific forms. It fell to Kepler to show, through his 
successes and through his failures, where the fruitful 
ground for science lay. It was ground that he himself 
could not reach. 

If we look into Kepler's turbulent life and work for 
those brief moments that best illuminate the man and 
the time, I would select passages from two letters. 
One, written to Guldin in 1626, described Kepler's life 
during the long siege of Linz. His house was situated 
at the city wall around which the fighting was raging, 
and a whole company of soldiers was stationed in it. 
"One had to keep all doors open for the soldiers, who 
through their continual coming day and night kept us 
from sleep and study." Here we find Kepler deep at 
work in technical chronology: "I set to work against 
Joseph Scaliger— one thought followed the next, and I 
did not even notice how time was passing." 

The other revealing view of Kepler is provided by a 
letter to Herwart von Hohenburg in 1605. Here we 
come as close as we can to putting the finger on the 
moment when the modern mechanical-mathematical 


conception of science breaks out of its earlier mold. 
Kepler wrote: "I am much occupied with the investi- 
gation of the physical causes. My aim in this is to 
show that the celestial machine is to be likened not to 
a divine organism but rather to a clockwork .... 
insofar as nearly all the manifold movements are car- 
ried out by means of a single, quite simple magnetic 
force; as in the case of a clockwork all motions [are 
caused] by a simple weight. Moreover, I show how this 
physical conception is to be presented through calcula- 
tion and geometry." 

The celestial machine, driven by a single terrestrial 
force, in the image of a clockwork! This was indeed a 
prophetic goal. When the Astronomia Nova (on which 
Kepler was working at the time) was published four 
years later, it significantly bore the subtitle Physica 
Coelestis. Here we find the search for one universal 
force-law to explain terrestrial gravity and the oceanic 
tides as well as the motion of the planets. It is a con- 
ception of unity that is perhaps even more striking 
than Newton's, for the simple reason that Kepler did 
not have a predecessor. 

Kepler did not, of course, succeed in his aim to find 

the physics that explains astronomical observations in 
terms of mechanics. The Achilles heel of his celestial 
physics was his Aristotelian conception of the law of 
inertia, which identified inertia with a tendency to 
come to rest: "Outside the field of force of another 
related body, every bodily substance, insofar as it is 
corporeal, by nature tends to remain at the same place 
at which it finds itself." (The quotation is from the 
Astronomia Nova.) This axiom deprived him of the 
concepts of mass and force in useful form, and without 
them his world machine was doomed. 

And yet, perhaps precisely because of the failure 
of his physics, he still had to see the world in one 
piece, holding before him an image in which there 
were three components: the universe as a physical ma- 
chine, the universe as mathematical harmony and the 
universe as a central theological order. Taken by itself, 
any one of the three was incomplete and insufficient. 
It was Kepler's vision of all three together that makes 
him so interesting to us when we compare his view 
of the world to ours, so much more successful in each 
detail but — perhaps necessarily and irretrievably — so 
much more fragmented. 


Kepler's description of how he came to take up the 
study of Mars, from his greatest book, The New As- 
tronomy. Kepler records in a personal way every- 
thing as it occurred to him, not merely the final re- 

8 Kepler on Mars 

Johannes Kepler 

Written in 1609 and translated by Owen Gingerich, 1967. 

Johannes Kepler 
(Translated by Owen Gingerich) 

Astronomia Nova, Chapter 7, first part 
On the Occasion When I Took up the Theory of Mars 

The divine voice that calls men to learn astronomy is, in truth, expressed in 
the universe itself, not by words or syllables, but by things themselves and by 
the agreement of the human intellect and senses with the ensemble of celestial 
bodies and phenomena. Nevertheless, there is a certain destiny which secretly 
drives men toward different arts and gives them the assurance that just as they 
are part of the works of creation, so also they participate in the divine Provi- 

Thus when I was old enough to taste the sweetness of philosophy, I embraced 
it all with an extreme passion, without taking a particular interest in astronomy. 
I have for it, certainly, a sufficient intelligence, and I understood without 
difficulty the geometry and astronomy imposed by the program of studies, which 
depends on figures, numbers and proportions. But these were the prescribed 
studies, and nothing indicated to me a particular inclination for astronomy. 


Since I was supported by a scholarship from the Duke of W'urttemberg and when 
I saw that my fellow students would excuse themselves when the Prince was so- 
liciting for foreign countries, although in face they simply refused for love of 
their native land, I decided very quickly, being of a tougher nature, to go im- 
mediately where I might be sent. 

The first place offered to me was an astronomical position into which, frank- 
ly, I was pushed only because of the authority of my teachers, not that I was 
frightened by the distance of the place— a fear I had condemned in the others 
(as I have said) — but because of the unexpected character and lowness of the 
position as well as the weakness of my knowledge in this part of philosophy. I 
accepted, therefore, being richer in ingenuity than in knowledge, and protest- 
ing highly that I would by no means abandon my right to another kind of life 
and ecclesiastical position that appeared to me much better. What was the suc- 
cess of my studies during the first two years appears in my Mysterium Cosmograph - 
icum. Moreover, what stimulus my teacher Maestlin applied to me for taking 
up astronomy, you will read in the same little book and in his letter prefixed to 
the Narratio of Rheticus. I have esteemed my discovery very high, and much 
more so when I saw that it was approved so highly by Maestlin. But he did not 
stimulate me as much by the untimely promise made by him to the readers, of 
a general astronomical work by me ( Uranicum vel Cosmicum Opus, as it was 
called), inasmuch as I was eager to inquire into the restoration of astronomy and 
to see if my discovery could be exposed to the discrimination of observations. 
Indeed it was demonstrated in the book itself that it agreed within the precision 
of common astronomy. 


Kepler on Mars 

Therefore at this time I began to think seriously of comparing it with observa- 
tions. And when, in 1597, I wrote to Tycho Brahe asking him to tell me what 
he thought of my little work, in his answer he mentioned, among other things, 
his observations, he fired me with an enormous desire to see them. Moreover, 
Tycho Brahe, himself an important part in my destiny, did not cease from then 
on to urge that I come to visit him. But since the distance of the two places 
would have deterred me, I ascribe it to divine Providence that he came to Bo- 
hemia. I thus arrived there just before the beginning of the year 1600, with 
the hope of obtaining the correct eccentricities of the planetary orbits. When, 
in the first week, I learned that he himself along with Ptolemy and Copernicus 
employed the mean motion of the sun, but in fact the apparent motion agreed 
more with my little book, (as shown by the book itself), I was authorized to 
use the observations in my manner. Now at that time, his personal aide, Chris- 
tian Severinus Longomontanus had taken up the theory of Mars, which was 
placed in his hands so that they might study the observation of the acronycal 
place, or opposition of Mars, with the sun in nine degrees of Leo. Had Chris- 
tian been occupied with another planet, I would have started with that same 

This is why I consider it again an effect of divine Providence that I arrived 
at Benatek at the time when he was directed toward Mars; because for us to 
arrive at the secret knowledge of astronomy, it is absolutely necessary to use 
the motion of Mars; otherwise it would remain eternally hidden. 


This article describes briefly the events which trans- 
pired immediately before the writing of the Principia. 

Newton and the Principia 
C. C. Gillispie 

An excerpt from his book The Edge of Objectivity, 1960. 

After 1676 Newton gave over contending for his theory 
of colors and withdrew into his alternate posture of re- 
nunciation. "I had for some years past," he wrote in 1679, 
"been endeavouring to bend myself from philosophy to 
other studies in so much that I have long grutched the 
time spent in that study unless it be perhaps at idle hours 
sometimes for a diversion." It is not known in detail how 
he spent those years. On theology and biblical antiquities 
certainly, on mathematics probably, on chemistry and on 
perfecting his optics perhaps, for it is in character that 
he should have nursed his disenchantment in public and 
continued his work in private. In 1679 he was recalled to 
science, but to dynamics this time, by a further letter 
from Hooke, now become Secretary of the Royal Society. 
Hooke approached him on two levels. Privately, the let- 
ter was an olive branch. Officially, it was the new secretary 
bespeaking the renewed collaboration of the most potent 
of his younger colleagues, sulking in his tent. 

Newton answered, correctly enough in form, but not 
very frankly, not at all cordially, affecting ignorance of 
an "hypothesis of springynesse" (Hooke's law of elasticity) 
on which Hooke had invited his opinion. So as to disguise 
without taking the edge off his snub, he threw in as a 
crumb "a fancy of my own," the solution of a curious 
problem he had toyed with in one of those idle hours. 
It concerned the trajectory of a body falling freely from 
a high tower, supposing the earth permeable and con- 
sidering only the diurnal rotation. This was in fact a 
famous puzzle suggested by the Copernician theory, the 
same problem which Galileo had so curiously and erro- 


Newton and the Principia 

neously answered with a semi-circle to the center of the 
earth. Since then it had been much discussed in obscure 
and learned places. And having brought it up himself, 
as if to flex a mental muscle in Hooke's face, Newton 
gave an answer as wrong as Galileo's. The trajectory, he 
casually said and drew it, will be a spiral to the center of 
the earth. 

Now, Hooke did not know the right answer. The forces 
are in fact complex: the force of gravity increases by the 
inverse square relationship as far as the surface of the 
earth and thereafter as the first power of the distance. 
Hooke, along with many others, surmised the former 
(though he was too feeble a mathematician to handle 
gravity other than as constant) but was ignorant — as New- 
ton then was — of the latter fact. He did have the happy 
thought of eliminating Coriolis forces by putting his 
tower on the equator. But Hooke did not need to solve 
the problem correctly to perceive that the initial tan- 
gential component of motion will not only, as Newton 
pointed out with an air of correcting vulgar errors, carry 
the body east of the foot of the tower, but by the same 
reasoning will insure that one point which the body can 
never traverse, either on a spiral or on any other path, is 
the center of the earth. Hooke was not the man to resist 
this opportunity. He had invited Newton to a private 
correspondence. He communicated Newton's reply to the 
Royal Society, and corrected his error publicly. 

It would be tedious to follow the ensuing correspond- 
ence: the outward forms of courtesy, the philosophical 
tributes to truth as the goal, the underlying venom, the 
angry jottings in the margin. Newton "grutched" admit- 
ting error far more than the time spent on philosophy. 
He never did solve the problem. But he left it as the most 
important unsolved problem in the history of science. 
For it drew his mind back to dynamics and gravity, back 


to where he had left those questions thirteen years before. 
And in the course of these geometrical investigations, he 
solved the force law of planetary motion: "I found the 
Proposition that by a centrifugal force reciprocally as the 
square of the distance a Planet must revolve in an Ellipsis 
about the center of the force placed in the lower umbilicus 
of the Ellipsis and with a radius drawn to that center 
describe areas proportional to the times." He would prove 
the point mass theorem only after 1685. But he had proved 
the law of gravity on the celestial scale, not just approx- 
imately for circular orbits as in 1666, but as a rigorous 
geometric deduction combining Kepler's laws with Huy- 
gens' law of centrifugal force. And he told no one, "but 
threw the calculations by, being upon other studies." 

It is one of the ironies attending the genesis of Newton's 
Principia that no one knew beforehand of his work on 
celestial mechanics. In inviting Newton's correspondence, 
Hooke may even have thought that he was taking his rival 
onto his own ground. For the problem of gravity was con- 
stantly under discussion. Hooke had certainly surmised 
that a gravitating force of attraction was involved in the 
celestial motions, and that it varied in power inversely 
as the square of the distance. So, too, had Christopher Wren, 
then one of the most active of the virtuosi, and the young 
astronomer, Edmund Halley. But none of them was mathe- 
matician enough to deduce the planetary motions from 
a force law. 

Far more than Boyle, Hooke was the complete Baconian. 
The only plausible explanation of his later conduct is 
that he truly did not understand the necessity for mathe- 
matical demonstration. He relied uniquely upon experi- 
ment to sort out the good from the bad ideas that crowded 
out of his fertile imagination. He seems to have been 
prepared to build even celestial mechanics out of experi- 
ments on falling bodies like those improvised to test out 


Newton and the Principia 

Newton's spiral. Nor could he see that the rigorous geo- 
metrical demonstrations of the Principia added anything 
to his own idea. They gave the same result. Once again, 
thought Hooke on seeing the manuscript, Newton had 
wrapped his intellectual property in figures and stolen it 

Halley was more sophisticated. He was also an attrac- 
tive and sympathetic young man. In August 1684 he went 
up from London to consult Newton. An account of this 
visit by John Conduitt, who later married Newton's niece, 
is generally accepted. 

Without mentioning either his own speculations, or those 
of Hooke and Wren, he at once indicated the object of his 
visit by asking Newton what would be the curve described 
by the planets on the supposition that gravity diminished 
as the square of the distance. Newton immediately answered, 
an Ellipse. Struck with joy and amazement, Halley asked him 
how he knew it? Why, replied he, I have calculated it; and 
being asked for the calculation, he could not find it, but 
promised to send it to him. 

While others were looking for the law of gravity, New- 
ton had lost it. And yielding to Halley's urging, Newton 
sat down to rework his calculations and to relate them to 
certain propositions On Motion (actually Newton's laws) 
on which he was lecturing that term. He had at first no 
notion of the magnitude of what he was beginning. But 
as he warmed to the task, the materials which he had been 
turning over in his mind in his twenty-five years at Cam- 
bridge moved into place in an array as orderly and planned 
as some perfect dance of figures. Besides proving Halley's 
theorem for him, he wrote the Mathematical Principles 
of Natural Philosophy. The Principia, it is always called, 
as if there were no other principles. And in a sense there 
are none. For that book contains all that is classical in 
classical physics. There is no work in science with which 
it may be compared. 


"I wrote it," said Newton, "in seventeen or eighteen 
months." He employed an amanuensis who has left an 
account of his working habits. 

I never knew him to take any recreation or pasttime 
either in riding out to take the air, walking, bowling, or any 
other exercise whatever, thinking all hours lost that was 
not spent in his studies, to which he kept so close that he 
seldom left his chamber except at term time, when he read 
in the schools as being Lucasianus Professor. ... He very 
rarely went to dine in the hall, except on some public days, 
and then if he has not been minded, would go very care- 
lessly, with shoes down at heels, stockings untied, surplice 
on, and his head scarcely combed. At some seldom times 
when he designed to dine in the hall, [he] would turn to 
the left hand and go out into the street, when making a 
stop when he found his mistake, would hastily turn back, 
and then sometimes instead of going into the hall, would 
return to his chamber again. 

Mostly Newton would have meals sent to his rooms and 
forget them. His secretary would ask whether he had 
eaten. "Have I?" Newton would reply. 

The Royal Society accepted the dedication, undertook 
to print the work, and like a true learned organization 
found itself without funds. The expense, therefore, as well 
as the editing came upon Halley. He was not a rich man, 
but he bore both burdens cheerfully, with devotion and 
tact. He had the disagreeable task of informing Newton 
that upon receipt of the manuscript Hooke had said of 
the inverse square law, "you had the notion from him," 
and demanded acknowledgment in a preface. Upon this 
Newton threatened to suppress the third book, the climax 
of the argument, which applied the laws of motion to the 
system of the world. He was dissuaded, as no doubt he 
meant to be, but one can understand how his feeling for 
Hooke turned from irritable dislike to scornful hatred: 


Newton and the Principia 

Now is not this very fine? Mathematicians, that find out, 
settle, and do all the business, must content themselves 
with being nothing but dry calculators and drudges; and 
another that does nothing but pretend and grasp at all 
things, must carry away all the invention, as well of those 
that were to follow him, as of those that went before. Much 
after the same manner were his letters writ to me, telling 
me that gravity, in descent from hence to the centre of 
the earth, was reciprocally in a duplicate ratio of the alti- 
tude, that the figure described by projectiles in this region 
would be an ellipsis, and that all the motions of the heavens 
were thus to be accounted for; and this he did in such a 
way, as if he had found out all, and knew it most certainly. 
And, upon this information, I must now acknowledge, in 
print, I had all from him, and so did nothing myself but 
drudge in calculating, demonstrating, and writing, upon 
the inventions of this great man. And yet, after all, the 
first of those three things he told me of is false, and very 
unphilosophical; the second is as false; and the third was 
more than he knew, or could affirm me ignorant of by any 
thing that past between us in our letters. 

The provocation was great, as was the strain under which 
it was given. A few years after completing the Principia 
Newton suffered a nervous collapse. He wrote very strange 
letters. One of them accused Locke of trying to embroil 
him with women — Newton, who was as oblivious to women 
as if they were occult qualities. Alarmed, his friends had 
arranged a move to London, to bring him more into com- 
pany. He gave up solitude in Cambridge with no regrets, 
became after a few years Master of the Mint, then Pres- 
ident of the Royal Society which once he had held at 
such a haughty distance. Knighted in 1705 he lived out 
his years until 1727, the incarnation of science in the eyes 
of his countrymen, a legend in his own lifetime. 

But he did very little more science. 


The Latin original of Newton's statement of the three 
Laws of Motion and the proof of Proposition One is 
followed here by the English translation by Andrew 
Motte and Florian Caiori. 

10 The Laws of Motion, and Proposition One 

Isaac Newton 

From his Mathematical Principles of Natural Philosophy 
translated by Florian Cajori, 1962. 





Corpus omne perseverare in statu suo quiescendi vel movendi uni- 
formiter in directum, nisi quatenus illud a viribus impressis cogitur 
statum suum mutare. 

PROJECTILIA perseverant in motibus suis, nisi quatenus a 
resistentia aeris retardantur, & vi gravitatis impelluntur deor- 
sum. Trochus, cujus partes cohaerendo perpetuo retrahunt sese a 
motibus rectilineis, non cessat rotari, nisi quatenus ab aere retardatur. 
Majora autem planetarum & cometarum corpora motus suos & 
progressivos & circulares in spatiis minus resistentibus factos con- 
servant diutius. 


The Laws of Motion, and Proposition One 

Mutationem motus proportionalem esse vi motrici impresses, & fieri 
secundum lineam rectam qua vis ilia imprimitur. 

Si vis aliqua motum quemvis generet ; dupla duplum, tripla 
triplum generabit, sive simul & semel, sive gradatim & successive 
impressa fuerit. Et hie motus (quoniam in eandem semper plagam 
cum vi generatrice determinatur) si corpus antea movebatur, motui 
ejus vel conspiranti additur, vel contrario subducitur, vel obliquo 
oblique adjicitur, & cum eo secundum utriusque determinationem 


Actioni contrariam semper & cequalem esse reactioimn : sive coiporum 
duorum actiones in se mutuo semper esse cequales & in partes 
con tr arias dirigi. 

Quicquid premit vel trahit alterum, tantundem ab eo premitur 
vel trahitur. Si quis lapidem digito premit, premitur & hujus 
digitus a lapide. Si equus lapidem funi alligatum trahit, retrahe- 
tur etiam & equus (ut ita dicam) sequaliter in lapidem : nam funis 
utrinque distentus eodem relaxandi se conatu urgebit equum versus 
lapidem, ac lapidem versus equum ; tantumque impediet progressum 
unius quantum promovet progressum alterius. Si corpus aliquod 
in corpus aliud impingens, motum ejus vi sua quomodocunque 
mutaverit, idem quoque vicissim in motu proprio eandem mutationem 
in partem contrariam vi alterius (ob aequalitatem pressionis mutuae) 
subibit. His actionibus aequales hunt mutationes, non veloci- 
tatum, sed motuum ; scilicet in corporibus non aliunde impeditis. 
Mutationes enim velocitatum, in contrarias itidem partes factae, 
quia motus aequaliter mutantur, sunt corporibus reciproce propor- 
tionales. Obtinet etiam hsec lex in attractionibus, ut in scholio 
proximo probabitur. 



Corpus viribtis conjunctis diagonalem parallelogrammi eodem tempore 
describere, quo latera separatis. 

Si corpus dato tempore, vi sola M A 
in loco A impressa, ferretur uniformi 
cum motu ab A ad B ; & vi sola N in 
eodem loco impressa, ferretur ab A ad C : 
compleatur parallelogrammum ABDC, 
& vi utraque feretur corpus illud eodem 
tempore in diagonali ab A ad D. Nam quoniam vis N agit secun- 
dum lineam A C ipsi BD parallelam, haec vis per legem 1 1 nihil 
mutabit velocitatem accedendi ad lineam illam BD a vi altera 
genitam. Accedet igitur corpus eodem tempore ad lineam BD, 
sive vis N imprimatur, sive non ; atque ideo in fine illius temporis 
reperietur alicubi in linea ilia BD. Eodem argumento in fine 
temporis ejusdem reperietur alicubi in linea CD, & idcirco in utri- 
usque linear concursu D reperiri necesse est. Perget autem motu 
rectilineo ab A ad D per legem i. 

S E C T I O II. 

De inventione virium centripetarum. 


Areas, quas corpora in gyros acta radii's ad immobile centrum 
virium ductis describunt, & in planis immobilibus consistere, 
& esse temporibus proportionates. 

Dividatur tempus in partes sequales, & prima temporis parte de- 
scribat corpus vi insita rectam A B. Idem secunda temporis parte, si 
nil impediret, recta pergeret ad c, (per leg. i.) describens lineam Be 


The Laws of Motion, and Proposition One 

aequalem ipsi AB ; adeo ut radiis A S, B S, c S ad centrum actis, 
confectae forent aequales areae A SB, BSc. Verum ubi corpus 
venit ad B, agat 
vis centripeta 
impulsu unico 
sed magno, effi- 
ciatque ut cor- 
pus de recta Be 
declinet & per- 
gat in recta B C. 
Ipsi B S paral- 
lela agatur c C, 
occurrens B C 
in C ; & com- 
plete secunda 
temporis parte, 
corpus (per le- 
gum corol. i.) 
reperietur in C, 
in eodem piano 
cum triangulo 
A SB. Junge 

SC; & triangulum SBC, ob parallelas SB, Cc, sequale erit trian- 
gulo SBc, atque ideo etiam triangulo SAB. Simili argumento si 
vis centripeta successive agat in C, D, E, &c. faciens ut corpus singulis 
temporis particulis singulas describat rectas CD, D E, E F, &c. 
jacebunt hae omnes in eodem piano ; & triangulum S CD triangulo 
SB C, & SDE ipsi SCD, & ^^^ipsi SDE zequaie erit. ^qua- 
libus igitur temporibus aequales areae in piano immoto describuntur : 
& componendo, sunt arearum summae quae vis SADS, SAES inter 
se, ut sunt tempora descriptionum. Augeatur jam numerus & minu- 
atur latitudo triangulorum in infinitum ; & eorum ultima perimeter 
A D E, (per corollarium quartum lemmatis tertii) erit linea curva : 
ideoque vis centripeta, qua corpus a tangente hujus curvae perpetuo 
retrahitur, aget indesinenter ; areae vero quaevis descriptae SADS, 
SAES temporibus descriptionum semper proportionales, erunt 
iisdem temporibus in hoc casu proportionales. Q. E. D. 




Every body continues in its state of rest, or of uniform motion in a right 
line, unless it is compelled to change that state by forces impressed upon it. 

Projectiles continue in their motions, so far as they are not retarded 
by the resistance of the air, or impelled downwards by the force of 
gravity. A top, whose parts by their cohesion are continually drawn 
aside from rectilinear motions, does not cease its rotation, otherwise than 
as it is retarded by the air. The greater bodies of the planets and comets, 
meeting with less resistance in freer spaces, preserve their motions both 
progressive and circular for a much longer time. 


The change of motion is proportional to the motive force impressed; and 
is made in the direction of the right line in which that force is impressed. 

If any force generates a motion, a double force will generate double the 
motion, a triple force triple the motion, whether that force be impressed 
altogether and at once, or gradually and successively. And this motion 
(being always directed the same way with the generating force), if the 
body moved before, is added to or subtracted from the former motion, 
according as they directly conspire with or are directly contrary to each 
other; or obliquely joined, when they are oblique, so as to produce a new 
motion compounded from the determination of both. 


To every action there is always opposed an equal reaction: or, the mutual 
actions of two bodies upon each other are always equal, and directed to 
contrary parts. 

Whatever draws or presses another is as much drawn or pressed by that 
other. If you press a stone with your finger, the finger is also pressed by the 


The Laws of Motion, and Proposition One 

stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will 
be equally drawn back towards the stone; for the distended rope, by the 
same endeavor to relax or unbend itself, will draw the horse as much 
towards the stone as it does the stone towards the horse, and will obstruct 
the progress of the one as much as it advances that of the other. If a body 
impinge upon another, and by its force change the motion of the other, that 
body also (because of the equality of the mutual pressure) will undergo an 
equal change, in its own motion, towards the contrary part. The changes 
made by these actions are equal, not in the velocities but in the motions of 
bodies; that is to say, if the bodies are not hindered by any other impedi- 
ments. For, because the motions are equally changed, the changes of the 
velocities made towards contrary parts are inversely proportional to the 
bodies. This law takes place also in attractions, as will be proved in the next 



A body, acted on by two forces simultaneously , will describe the diagonal 
of a parallelogram in the same time as it would describe the sides by those 
forces separately. 

If a body in a given time, by the force M impressed apart in the place A, 
should with an uniform motion be carried from A to B, and by the force N 
impressed apart in the same place, should be carried from A to C, let the 

parallelogram ABCD be completed, and, 
by both forces acting together, it will in the 
same time be carried in the diagonal from 
A to D. For since the force N acts in the 
direction ofthe line AC, parallel to BD, 
this force (by the second Law) will not at 
all alter the velocity generated by the other 
force M, by which the body is carried towards the line BD. The body there- 
fore will arrive at the line BD in the same time, whether the force N be 
impressed or not; and therefore at the end of that time it will be found 
somewhere in the line BD. By the same argument, at the end of the same 
time it will be found somewhere in the line CD. Therefore it will be found 
in the point D, where both lines meet. But it will move in a right line from 
A to D, by Law i. 



The determination of centripetal forces. 


The areas which revolving bodies describe by radii drawn to an immovable 
centre of force do lie in the same immovable planes, and are proportional 
to the times in which they are described. 

For suppose the time to be divided into equal parts, and in the first part 
of that time let the body by its innate force describe the right line AB. In 
the second part of that time, the same would (by Law i), if not hindered, 

^ e 


proceed directly to c, along the line Br equal to AB ; so that by the radii AS, 
BS, cS, drawn to the centre, the equal areas ASB, BSr, would be described. 
But when the body is arrived at B, suppose that a centripetal force acts at 
once with a great impulse, and, turning aside the body from the right line 
Br, compels it afterwards to continue its motion along the right line BC. 


The Laws of Motion, and Proposition One 

Draw cC parallel to BS, meeting BC in C; and at the end of the second part 
of the time, the body (by Cor. i of the Laws) will be found in C, in the 
same plane with the triangle ASB. Join SC, and, because SB and O are 
parallel, the triangle SBC will be equal to the triangle SBr, and therefore 
also to the triangle SAB. By the like argument, if the centripetal force acts 
successively in C, D, E, &c, and makes the body, in each single particle of 
time, to describe the right lines CD, DE, EF, &c, they will all lie in the same 
plane; and the triangle SCD will be equal to the triangle SBC, and SDE to 
SCD, and SEF to SDE. And therefore, in equal times, equal areas are de- 
scribed in one immovable plane: and, by composition, any sums SADS, 
SAFS, of those areas, are to each other as the times in which they are de- 
scribed. Now let the number of those triangles be augmented, and their 
breadth diminished in infinitum; and (by Cor. iv, Lem. in) their ultimate 
perimeter ADF will be a curved line: and therefore the centripetal force, 
by which the body is continually drawn back from the tangent of this curve, 
will act continually; and any described areas SADS, SAFS, which are 
always proportional to the times of description, will, in this case also, be 
proportional to those times. Q.E.D. 


Anatole France is best known as the writer of novels 
such as Penguin Island . This brief passage shows that 
he, along with many writers, is interested in science. 

The Garden of Epicurus 

Anatole France 

An essay written in 1920. 

E find it hard to picture to ourselves 
the state of mind of a man of older 
days who firmly believed that the 
Earth was the center of the Universe, 
and that all the heavenly bodies 
revolved round it. He could feel beneath his 
feet the writhings of the damned amid the flames; 
very likely he had seen with his own eyes and 
smelt with his own nostrils the sulphurous fumes 
of Hell escaping from some fissure in the rocks. 
Looking upwards, he beheld the twelve spheres, 
— first that of the elements, comprising air and fire, 
then the sphere of the Moon, of Mercury, of Venus, 
which Dante visited on Good Friday of the year 
1300, then those of the Sun, of Mars, of Jupiter, 
and of Saturn, then the incorruptible firmament, 
wherein the stars hung fixed like so many lamps. 
Imagination carried his gaze further still, and his 
mind's eye discerned in a remoter distance the Ninth 
Heaven, whither the Saints were translated to 
glory, the primum mobile or crystalline, and finally the 
Empyrean, abode of the Blessed, to which, after 


The Garden of Epicurus 

death, two angels robed in white (as he steadfastly . 
hoped) would bear his soul, as it were a little child, 
washed by baptism and perfumed with the oil of 
the last sacraments. In those times God had no 
other children but mankind, and all His creation 
was administered after a fashion at once puerile 
and poetical, like the routine of a vast cathedral. 
Thus conceived, the Universe was so simple that it 
was fully and adequately represented, with its true 
shape and proper motion, in sundry great clocks 
compacted and painted by the craftsmen of the 
Middle Ages. 

We are done now with the twelve spheres and 
the planets under which men were born happy or 
unhappy, jovial or saturnine. The solid vault of the 
firmament is cleft asunder. Our eyes and thoughts 
plunge into the infinite abysses of the heavens. 
Beyond the planets, we discover, instead of the 
Empyrean of the elect and the angels, a hundred 
millions of suns rolling through space, escorted 
each by its own procession of dim satellites, invis- 
ible to us. Amidst this infinitude of systems our 
Sun is but a bubble of gas and the Earth a drop of 
mud. The imagination is vexed and startled when 
the astronomers tell us that the luminous ray 
which reaches us from the pole-star has been 
half a century on the road ; and yet that noble 
star is our next neighbour, and with Sirius and 
Arcturus, one of the least remote of the suns 


that are sisters of our own. There are stars we 
still see in the field of our telescopes which 
ceased to shine, it may be, three thousand years 

Worlds die, — for are they not born ? Birth and 
death are unceasingly at work. Creation is never 
complete and perfect ; it goes on for ever under in- 
cessant changes and modifications. The stars go 
out, but we cannot say if these daughters of light, 
when they die down into darkness, do not enter on 
a new and fecund existence as planets, — if the 
planets themselves do not melt away and become 
stars again. All wg know is this ; there is no 
more repose in the spaces of the sky than on earth, 
and the same law of strife and struggle governs 
the infinitude of the cosmic universe. 

There are stars that have gone out under our 
eyes, while others are even now flickering like the 
dying flame of a taper. The heavens, which men 
deemed incorruptible, know of no eternity but the 
eternal flux of things. 

That organic life is diffused through all parts of 
the Universe can hardly be doubted, — unless indeed 
organic life is a mere accident, an unhappy chance, 
a deplorable something that has inexplicably arisen 
in the particular drop of mud inhabited by our- 

But it is more natural to suppose that life has 
developed in the planets of our solar system, the 


The Garden of Epicurus 

Earth's sisters and like her, daughters of the Sun, 
and that it arose there under conditions analogous 
in the main to those in which it manifests itself 
with us, — under animal and vegetable forms. A 
meteoric stone has actually reached us from the 
heavens containing carbon. To convince us in 
more gracious fashion, the Angels that brought St. 
Dorothy garlands of flowers from Paradise would 
have to come again with their celestial blossoms. 
Mars to all appearance is habitable for living things 
of kinds comparable to our terrestrial animals and 
plants. It seems likely that, being habitable, it is 
inhabited. Rest assured, there too species is 
devouring species, and individual individual, at 
this present moment. 

The uniformity of composition of the stars is 
now proved by spectrum analysis. Hence we are 
bound to suppose that the same causes that have 
produced life from the nebulous nucleus we call the 
Earth engender it in all the others. 

When we say life, we mean the activity of 
organized matter under the conditions in which 
we see it manifested in our own world. But it is 
equally possible that life may be developed in a 
totally different environment, at extremely high or 
extremely low temperatures, and under forms un- 
thinkable by as. It may even be developed under 
an ethereal form, close beside us, in our atmosphere ; 
and it is possible that in this way we are surrounded 


by angels, — beings we shall never know, because to 
know them implies a point of common contact, a 
mutual relation, such as there can never be between 
them and us. 

Again, it is possible that these millions of suns, 
along with thousands of millions more we cannot 
see, make up altogether but a globule of blood or 
lymph in the veins of an animal, of a minute 
insect, hatched in a world of whose vastness we 
can frame no conception, but which nevertheless 
would itself, in proportion to some other world, 
be no more than a speck of dust. 

Nor is there anything absurd in supposing that 
centuries of thought and intelligence may live and 
die before us in the space of a minute of time, in 
the confines of an atom of matter. In themselves 
things are neither great nor small, and when we 
say the Universe is vast we speak purely from 
a human standpoint. If it were suddenly reduced 
to the dimensions of a hazel-nut, all things keeping 
their relative proportions, we should know nothing 
of the change. The pole-star, included together 
with ourselves in the nut, would still take fifty 
years to transmit its light to us as before. And 
the Earth, though grown smaller than an atom, 
would be watered with tears and blood just as 
copiously as it is to-day. The wonder is, not that 
the field of the stars is so vast, but that man has 
measured it. 


A physical concept, such as gravitation, can be a 
powerful tool, illuminating many areas outside of 
that in which it was initially developed. As these 
authors show, physicists can be deeply involved 
when writing about their field. 

12 Universal Gravitation 

Richard P. Feynman, Robert B. Leighton, and Matthew Sands 

An excerpt from their book The Feynman Lectures on Physics, Volume 1, 1963. 

What else can we understand when we understand gravity? Everyone knows 
the earth is round. Why is the earth round? That is easy; it is due to gravitation. 
The earth can be understood to be round merely because everything attracts 
everything else and so it has attracted itself together as far as it can! If we go even 
further, the earth is not exactly a sphere because it is rotating, and this brings in 
centrifugal effects which tend to oppose gravity near the equator. It turns out that 
the earth should be elliptical, and we even get the right shape for the ellipse. 
We can thus deduce that the sun, the moon, and the earth should be (nearly) 
spheres, just from the law of gravitation. 

What else can you do with the law of gravitation? If we look at the moons 
of Jupiter we can understand everything about the way they move around that 
planet. Incidentally, there was once a certain difficulty with the moons of Jupiter 
that is worth remarking on. These satellites were studied very carefully by Roemer, 
who noticed that the moons sometimes seemed to be ahead of schedule, and some- 
times behind. (One can find their schedules by waiting a very long time and finding 
out how long it takes on the average for the moons to go around.) Now they were 
ahead when Jupiter was particularly close to the earth and they were behind when 
Jupiter was farther from the earth. This would have been a very difficult thing to 
explain according to the law of gravitation — it would have been, in fact, the death 
of this wonderful theory if there were no other explanation. If a law does not work 
even in one place where it ought to, it is just wrong. But the reason for this dis- 
crepancy was very simple and beautiful: it takes a little while to see the moons of 
Jupiter because of the time it takes light to travel from Jupiter to the earth. When 
Jupiter is closer to the earth the time is a little less, and when it is farther from the 
earth, the time is more. This is why moons appear to be, on the average, a little 
ahead or a little behind, depending on whether they are closer to or farther from 
the earth. This phenomenon showed that light does not travel instantaneously, 
and furnished the first estimate of the speed of light. This was done in 1656. 

If all of the planets push and pull on each other, the force which controls, 
let us say, Jupiter in going around the sun is not just the force from the sun ; 
there is also a pull from, say, Saturn. This force is not really strong, since the sun 
is much more massive than Saturn, but there is some pull, so the orbit of Jupiter 
should not be a perfect ellipse, and it is not; it is slightly off", and "wobbles" around 
the correct elliptical orbit. Such a motion is a little more complicated. Attempts 
were made to analyze the motions of Jupiter, Saturn, and Uranus on the basis 
of the law of gravitation. The effects of each of these planets on each other were 
calculated to see whether or not the tiny deviations and irregularities in these 
motions could be completely understood from this one law. Lo and behold, for 
Jupiter and Saturn, all was well, but Uranus was "weird." It behaved in a very 
peculiar manner. It was not travelling in an exact ellipse, but that was under- 
standable, because of the attractions of Jupiter and Saturn. But even if allowance 
were made for these attractions, Uranus still was not going -right, so the laws of 
gravitation were in danger of being overturned, a possibility that could not be 
ruled out. Two men, Adams and Leverrier, in England and France, independently, 


Fig. 7-6. A double-star system. 

arrived at another possibility: perhaps there is another planet, dark and invisible, 
which men had not seen. This planet, N, could pull on Uranus. They calculated 
where such a planet would have to be in order to cause the observed perturba- 
tions. They sent messages to the respective observatories, saying, "Gentlemen, 
point your telescope to such and such a place, and you will see a new planet." 
It often depends on with whom you are working as to whether they pay any atten- 
tion to you or not. They did pay attention to Leverrier; they looked, and there 
planet N was! The other observatory then also looked very quickly in the next 
few days and saw it too. 

This discovery shows that Newton's laws are absolutely right in the solar 
system; but do they extend beyond the relatively small distances of the nearest 
planets? The first test lies in the question, do stars attract each other as well as 
planets? We have definite evidence that they do in the double stars. Figure 7-6 
shows a double star — two stars very close together (there is also a third star in 
the picture so that we will know that the photograph was not turned). The stars 
are also shown as they appeared several years later. We see that, relative to the 
"fixed" star, the axis of the pair has rotated, i.e., the two stars are going around 
each other. Do they rotate according to Newton's laws? Careful measurements 
of the relative positions of one such double star system are shown in Fig. 7-7. 
There we see a beautiful ellipse, the measures starting in 1862 and going all the 
way around to 1904 (by now it must have gone around once more). Everything 
coincides with Newton's laws, except that the star Sirius A is not at the focus. 
Why should that be? Because the plane of the ellipse is not in the "plane of the 
sky." We are not looking at right angles to the orbit plane, and when an ellipse 
is viewed at a tilt, it remains an ellipse but the focus is no longer at the same place. 
Thus we can analyze double stars, moving about each other, according to the 
requirements of the gravitational law. 


Fig. 7-7. Orbit of Sirius 8 with respect to Sirius A. 


Universal Gravitation 

Fig. 7-8. A globular star cluster. 

That the law of gravitation is true at even bigger distances is indicated in 
Fig. 7-8. If one cannot see gravitation acting here, he has no soul. This figure 
shows one of the most beautiful things in the sky — a globular star cluster. All of 
the dots are stars. Although they look as if they are packed solid toward the center, 
that is due to the fallibility of our instruments. Actually, the distances between 
even the centermost stars are very great and they very rarely collide. There are 
more stars in the interior than farther out, and as we move outward there are 
fewer and fewer. It is obvious that there is an attraction among these stars. 
It is clear that gravitation exists at these enormous dimensions, perhaps 100,000 
times the size of the solar system. Let us now go further, and look at an entire 
galaxy, shown in Fig. 7-9. The shape of this galaxy indicates an obvious tendency 
for its matter to agglomerate. Of course we cannot prove that the law here is 
precisely inverse square, only that there is still an attraction, at this enormous 
dimension, that holds the whole thing together. One may say, "Well, that is all 
very clever but why is it not just a ball?" Because it is spinning and has angular 
momentum which it cannot give up as it contracts; it must contract mostly in a 
plane. (Incidentally, if you are looking for a good problem, the exact details of 
how the arms are formed and what determines the shapes of these galaxies has 
not been worked out.) It is, however, clear that the shape of the galaxy is due to 
gravitation even though the complexities of its structure have not yet allowed 

Fig. 7-9. A galaxy. 


us to analyze it completely. In a galaxy we have a scale of perhaps 50,000 to 
100,000 light years. The earth's distance from the sun is 83 light minutes, so you 
can see how large these dimensions are. 

Gravity appears to exist at even bigger dimensions, as indicated by Fig. 7-10, 
which shows many "little" things clustered together. This is a cluster of galaxies, 
just like a star cluster. Thus galaxies attract each other at such distances that they 
too are agglomerated into clusters. Perhaps gravitation exists even over distances 
of lens of millions of light years; so far as we now know, gravity seems to go out 
forever inversely as the square of the distance. 

Not only can we understand the nebulae, but from the law of gravitation we 
can even get some ideas about the origin of the stars. If we have a big cloud of dust 
and gas, as indicated in Fig. 7—11, the gravitational attractions of the pieces of 
dust for one another might make them form little lumps. Barely visible in the figure 
are "little" black spots which may be the beginning of the accumulations of dust 
and gases which, due to their gravitation, begin to form stars. Whether we have 
ever seen a star form or not is still debatable. Figure 7-12 shows the one piece of 
evidence which suggests that we have. At the left is a picture of a region of gas 
with some stars in it taken in 1947, and at the right is another picture, taken only 
7 years later, which shows two new bright spots. Has gas accumulated, has gravity 
acted hard enough and collected it into a ball big enough that the stellar nuclear 
reaction starts in the interior and turns it into a star? Perhaps, and perhaps not. 
It is unreasonable that in only seven years we should be so lucky as to see a star 
change itself into visible form; it is much less probable that we should see two! 

Fig. 7-10. A cluster of galaxies. 

Fig. 7-1 1. An interstellar dust cloud. 

Fig. 7-12. The formation of new stars? 


The earth, with all its faults, is a rather pleasant 
habitation for man. If things were only slightly 
different, our planet might not suit man nearly as 
well as it now does. 

13 An Appreciation of the Earth 

Stephen H. Dole 

An excerpt from his book Habitable Planets for Man, 1964. 

We take our home for granted most of the time. We complain about the 
weather, ignore the splendor of our sunsets, the scenery, and the natural 
beauties of the lands and seas around us, and cease to be impressed by 
the diversity of living species that the Earth supports. This is natural, 
of course, since we are all products of the Earth and have evolved in 
conformity with the existing environment. It is our natural habitat, and 
all of it seems very commonplace and normal. Yet how different our 
world would be if some of the astronomical parameters were changed 
even slightly. 

Suppose that, with everything else being the same, the Earth had started 
out with twice its present mass, giving a surface gravity of 1.38 times 
Earth normal. Would the progression of animal life from sea to land 
have been so rapid? While the evolution of marine life would not have 
been greatly changed, land forms would have to be more sturdily con- 
structed, with a lower center of mass. Trees would tend to be shorter and 
to have strongly buttressed trunks. Land animals would tend to develop 
heavier leg bones and heavier musculature. The development of flying 
forms would certainly have been different, to conform with the denser 
air (more aerodynamic drag at a given velocity) and the higher gravity 
(more lifting surface necessary to support a given mass). A number of 
opposing forces would have changed the face of the land. Mountain- 
forming activity might be increased, but mountains could not thrust so 
high and still have the structural strength to support their own weight; 
raindrop and stream erosion would be magnified, but the steeper density 
gradient in the atmosphere would change the weather patterns; wave 
heights in the oceans would be lower, and spray trajectories would be 


shortened, resulting in less evaporation and a drier atmosphere; and cloud 
decks would tend to be lower. The land-sea ratio would probably be smaller. 
The length of the sidereal month would shorten from 27.3 to 19.4 days 
(if the Moon's distance remained the same). There would be differences 
in the Earth's magnetic field, the thickness of its crust, the size of its core, 
the distribution of mineral deposits in the crust, the level of radioactivity 
in the rocks, and the size of the ice caps on islands in the polar regions. 
Certainly man's counterpart (assuming that such a species would have 
evolved in this environment) would be quite different in appearance and 
have quite different cultural patterns. 

Conversely, suppose that the Earth had started out with half its present 
mass, resulting in a surface gravity of 0.73 times Earth normal. Again the 
course of evolution and geological history would have changed under 
the influences of the lower gravity, the thinner atmosphere, the reduced 
erosion by falling water, and the probably increased level of background 
radiation due to more crustal radioactivity and solar cosmic particles. 
Would evolution have proceeded more rapidly? Would the progression 
from sea to land and the entry of animal forms into the ecological niches 
open to airborne species have occurred earlier? Undoubtedly animal 
skeletons would be lighter, and trees would be generally taller and more 
spindly; and again, man's counterpart, evolved on such a planet, would 
be different in many ways. 

What if the inclination of the Earth's equator initially had been 60 
degrees instead of 23.5 degrees? Seasonal weather changes would then 
be all but intolerable, and the only climatic region suitable for life as we 
know it would be in a narrow belt within about 5 degrees of the equator. 
The rest of the planet would be either too hot or too cold during most of 
the year, and with such a narrow habitable range, it is probable that life 
would have had difficulty getting started and, once started, would have 
tended to evolve but slowly. 

Starting out with an inclination of degrees would have influenced 
the course of development of the Earth's life forms in only a minor way. 
Seasons would be an unknown phenomenon; weather would undoubtedly 
be far more predictable and constant from day to day. All latitudes would 
enjoy a constant spring. The region within 12 degrees of the equator would 
become too hot for habitability but, in partial compensation, some 
regions closer to the poles would become more habitable than they are 

Suppose the Earth's mean distance from the Sun were 10 per cent less 
than it is at present. Less than 20 per cent of the surface area (that between 
latitudes 45 degrees and 64 degrees) would then be habitable. Thus there 
would be two narrow land regions favorable to life separated by a wide 


An Appreciation of the Earth 

and intolerably hot barrier. Land life could evolve independently in these 
two regions. The polar ice would not be present, so the ocean level would 
be higher than it is now, thus decreasing the land area. 

If the Earth were 10 per cent farther away from the Sun than it is, 
the habitable regions would be those within 47 degrees of the equator. 
(The present limit of habitability is assumed to be, on an average, within 
60 degrees of the equator.) 

If the Earth's rotation rate were increased so as to make the day 3 hours 
long instead of 24 hours, the oblateness would be pronounced, and changes 
of gravity as a function of latitude would be a common part of a traveler's 
experience. Day-to-night temperature differences would become small. 

On the other hand, if the Earth's rotation rate were slowed to make 
the day 100 hours in length, day-to-night temperature changes would be 
extreme; weather cycles would have a more pronounced diurnal pattern. 
The Sun would seem to crawl across the sky, and few life forms on land 
could tolerate either the heat of the long day or the cold of the long night. 

The effects of reducing the eccentricity of the Earth's orbit to (from 
its present value of 0.0167) would be scarcely noticeable. If orbital 
eccentricity were increased to 0.2 without altering the length of the semi- 
major axis (making perihelion coincide with summer solstice in the Northern 
Hemisphere to accentuate the effects), the habitability apparently would 
not be affected in any significant manner. 

Increasing the mass of the Sun by 20 per cent (and moving the Earth's 
orbit out to 1.408 astronomical units to keep the solar constant at its 
present level) would increase the period of revolution to 1.54 years and 
decrease the Sun's apparent angular diameter to 26 minutes of arc (from 
its present 32 minutes of arc). Our primary would then be a class F5 star 
with a total main-sequence lifetime of about 5.4 billion years. If the age 
of the solar system were 4.5 billion years, then the Earth, under these 
conditions, could look forward to another billion years of history. Since 
neither of these numbers is known to the implied accuracy, however, a 
10 per cent error in each in the wrong direction could mean that the end 
was very near indeed. An F5 star may well be more "active" than our 
Sun, thus producing a higher exosphere temperature in the planetary 
atmosphere; but this subject is so little understood at present that no 
conclusions can be drawn. Presumably, apart from the longer year, the 
smaller apparent size of the Sun, its more pronounced whiteness, and the 
"imminence" of doom, life could be much the same. 

If the mass of the Sun were reduced by 20 per cent (this time decreasing 
the Earth's orbital dimensions to compensate), the new orbital distance 
would be 0.654 astronomical unit. The year's length would then become 
0.59 year (215 days), and the Sun's apparent angular diameter, 41 minutes 


of arc. The primary would be of spectral type G8 (slightly yellower than 
our Sun is now) with a main-sequence lifetime in excess of 20 billion years. 
The ocean tides due to the primary would be about equal to those due to 
the Moon; thus spring tides would be somewhat higher and neap tides 
lower than they are at present. 

What if the Moon had been located much closer to the Earth than it 
is, say, about 95,000 miles away instead of 239,000 miles? The tidal 
braking force would probably have been sufficient to halt the rotation 
of the Earth with respect to the Moon, and the Earth's day would equal 
its month, now 6.9 days in length (sidereal). Consequently, the Earth would 
be uninhabitable. 

Moving the Moon farther away than it is would have much less pro- 
found results: the month would merely be longer and the tides lower. 
Beyond a radius of about 446,000 miles, the Earth can not hold a satellite 
on a circular orbit. 

Increasing the mass of the Moon by a factor of 10 at its present distance 
would have an effect similar to that of reducing its distance. However, 
the Earth's day and month would then be equal to 26 days. Decreasing 
the Moon's mass would affect only the tides. 

What if the properties of some of the other planets of the solar system 
were changed? Suppose the mass of Jupiter were increased by a factor 
of 1050, making it essentially a replica of the Sun. The Earth could still 
occupy its present orbit around the Sun, but our sky would be enriched 
by the presence of an extremely bright star, or second sun, of magnitude 
— 23.7, which would supply at most only 6 per cent as much heat as the 
Sun. Mercury and Venus could also keep their present orbits; the re- 
maining planets could not, although those exterior to Saturn could take 
up new orbits around the new center of mass. 

All in all, the Earth is a wonderful planet to live on, just the way it is. 
Almost any change in its physical properties, position, or orientation would 
be for the worse. We are not likely to find a planet that suits us better, 
although at some future time there may be men who prefer to live on 
other planets. At the present time, however, the Earth is the only home 
we have; we would do well to conserve its treasures and to use its resources 


Close-up television photographs of Mars reveal craters 
like those on the moon, but also other unexpected features. 

14 Mariners 6 and 7 Television Pictures; Preliminary 

R. B. Leighton and others* 

An article from Science, 1969. 

Before the space era, Mars was 
thought to be like the earth; after Mari- 
ner 4, Mars seemed to be like the moon; 
Mariners 6 and 7 have shown Mars to 
have its own distinctive features, un- 
known elsewhere within the solar 

The successful flyby of Mariner 4 
past Mars in July 1965 opened a new 
era in the close-range study of plane- 
tary surfaces with imaging techniques. 
In spite of the limited return of data, 
Mariner 4 established the basic worka- 
bility of one such technique, which in- 
volved use of a vidicon image tube, 
on-board digitization of the video sig- 
nal, storage of the data on magnetic 
tape, transmission to the earth at re- 
duced bit rate by way of a directional 
antenna, and reconstruction into a pic- 
ture under computer control. Even 
though the Mariner 4 pictures covered 
only about 1 percent of Mars's area, 
they contributed significantly to our 
knowledge of that planet's surface and 
history (1, 2, 19, 21). 

The objectives of the Mariner 6 and 
7 television experiment were to apply 
the successful techniques of Mariner 4 
to further explore the surface and at- 
mosphere of Mars, both at long range 

* Drs. Leighton, Horowitz, Murray, and Sharp 
are affiliated with the California Institute of 
Technology, Pasadena; Mr. Herriman and Dr. 
Young, with the Jet Propulsion Laboratory, Pasa- 
dena: Mr. Smith, with New Mexico State Uni- 
versity, Las Cruces; Dr. Davies, with the RAND 
Corporation, Santa Monica, California; and Dr. 
Leovy, with the University of Washington, Seattle. 

and at close range, in order to deter- 
mine the basic character of features 
familiar from ground-based telescopic 
studies: to discover possible further 
clues as to the internal state and past 
history of the planet; and to provide 
information germane to the search for 
extraterrestrial life. 

The Mariner 6 and 7 spacecraft suc- 
cessfully flew past Mars on 31 July and 
5 August 1969, respectively: first results 
of the television experiment, based upon 
qualitative study of the uncalibrated 
pictures, have been reported (3, 4). The 
purpose of this article is to draw to- 
gether the preliminary television results 
from the two spacecraft: to present ten- 
tative data concerning crater size distri- 
butions, wall slopes, and geographic 
distribution: to discuss evidences of haze 
or clouds; to describe new, distinctive 
types of topography seen in the pic- 
tures; and to discuss the implications 
of the results with respect to the present 
state, past history, and possible biologi- 
cal status of Mars. 

The data presented here and in the 
two earlier reports were obtained from 
inspection and measurement of a par- 
tial sample of pictures in various stages 
of processing. As such, the results must 
be regarded as tentative, subject to con- 
siderable expansion and possible modi- 
fication as more complete sets, and 
better-quality versions, of the pictures 
become available over a period of sev- 
eral months. They are offered at this 


time because of their unique nature, 
their wide interest, and their obvious 
relevance to the forthcoming Mariner 
1971 (orbiter) and Viking 1973 (lander) 

Television System Design 

The experience and results of Mari- 
ner 4 strongly influenced the basic de- 
sign of the Mariner 6 and 7 television 
experiment. The earlier pictures showed 
Mars to be heavily cratered, but to 
have subdued surface relief and low 
photographic contrast, and possibly to 
have a hazy atmosphere. It was also 
found that a vidicon-type camera tube 
has a most important property: the 
"target noise," analogous to photo- 
graphic grain, is less than that of a 
photographic emulsion by perhaps a 
factor of 10 (2) and is the same from 
picture to picture. Thus the 64-level (6- 
bit) encoding scheme of Mariner 4 was 
able to cope with the extremely low 
contrast conditions because intensity 
calibration and contrast enhancement 
by computer techniques could be effec- 
tively applied to the data to produce 
pictures of useful quality. 

Early design studies for Mariner 6 
and 7 centered around 256-level (8-bit) 
encoding — at least a tenfold increase in 
data return over that from Mariner 4; 
overlapping two-color coverage along 
the picture track (similar to that of 
Mariner 4); use of two cameras of dif- 
ferent focal lengths to provide higher- 
resolution views of areas nested within 
overlapping, wider-angle frames; and 
use of the camera of longer focal 
length to obtain a few full-disk photo 
graphs showing all sides of Mars as the 
spacecraft approached the planet. A 
third filter color, "blue," was added to 
the "red" and "green" of Mariner 4 
for the purpose of studying atmospheric 

Limitations of volume, money, and 
schedule prevented use of a suitable 
digital recorder system with the nec- 
essary data storage capacity, but. 
through a hybrid system which uses both 
digital and analog tape recorders, it ap- 

peared possible to achieve sufficient data 
storage capacity, albeit at the expense 
of complexity. 

In its final form, the television ex- 
periment employed a two-camera system 
in which the picture formats and elec- 
tronic circuits of the cameras were iden- 
tical (for economy and for efficient use 
of the tape recorders); a digital tape 
recorder to store the six lowest-order 
bits of an 8-bit encoded word for every 
seventh picture element ("pixel") 
along each TV picture line (referred to 
as 1/7 digital data; see 5); and a second, 
similar tape recorder to store analog 
data for all pixels (6). . . . 

Some technical data relating to the 
camera system are given in Leighton et 
al. (5), and more complete data will 
be given elsewhere (6). Briefly, one 
camera, called camera A, has a field of 
view 11° x 14° and a rotary shutter 
which carries four colored filters in the 
sequence red. green, blue, green, and 
so on. Alternating exposures with cam- 
era A is camera B, which has a focal 
length 10 times as great and a field of 
view l°.l x l.°4. Camera B carries 
only a minus-blue haze filter.... 

To illustrate the nature of the picture 
restoration process, we list some of the 
steps in the computer reduction: Restore 
the two highest-order bits to the digital 
data (7); remove effects of AGC and 
"cuber" in the analog data: combine 
digital and analog data; measure and 
remove electronic "pickup" noise (7); 
measure pixel locations of reseau marks 
on flight pictures and calibration pic- 
tures (8)\ bring pictorial calibration 
and flight data, by interpolation, into 
agreement with the known reseau pat- 
tern: measure and correct for optical 
distortions: measure and remove effects 
of residual image from calibration and 
flight data: evaluate the sensitometric 
response of each pixel from calibration 
data and deduce the true photometric 
exposure for each flight pixel (9); cor- 
rect for the effects of shutter-speed vari- 
ations and light leakage (camera B); 
and evaluate and correct for the modu- 
lation-transfer function of the camera 
system. . . . 


Mission Design and 
Television Data Return 

As was described in Leighton et al. 
(3), the planetary encounter period for 
each spacecraft was divided into two 
parts: a far-encounter (FE) period be- 
ginning 2 or 3 days prior to, and ex- 
tending to within a few hours of, closest 
approach, and a near-encounter (NE) 
period bracketing the time of closest 
approach .... 

In all, 50 FE pictures, 26 NE 
pictures, and 428 useful (10) real-time 
1/7 digital pictures were returned from 
Mariner 6, and 93 FE pictures, 33 NE 
pictures, and 749 useful real-time digital 
pictures were returned from Mariner 7. 
This further ninefold increase in the 
number of FE pictures and 18 percent 
increase in the number of NE pictures 
over the original plan represents a total 
data return 200 times that of Mariner 
4, not counting the real-time digital 

The pictures are designated by space- 
craft, camera mode, and frame number. 

Mariners 6 and 7 Television Pictures; Preliminary Analysis 

Thus "6N17' means Mariner 6 NE 
frame 17: "7F77" means Mariner 7 FE 
frame 77; and so on. The first NE pic- 
ture from each spacecraft was a camera- 
A, blue-filter picture. Thus, in near- 
encounter, all odd-numbered frames 
are camera-A (wide-angle, low-resolu- 
tion) frames. . . . 

The approximate near-encounter pic- 
ture locations for the two spacecraft are 
shown in Fig. 3, and the relevant data 
are given in Tables 1 and 2. The pic- 
ture tracks were chosen, in concert with 
investigators for other on-board experi- 
ments, on the basis of several consider- 
ations and constraints. First, the choice 
of possible arrival dates was limited by 
engineering considerations to the inter- 
val 31 July to 15 August 1969. Second, 
on any given arrival date, the time 
of closest approach was limited to an 
interval of about 1 hour by the require- 
ment that the spacecraft be in radio 
view of Goldstone tracking station dur- 
ing a period of several hours which 
bracketed the time of closest approach. 
These two constraints and the approxi- 
mate 24-hour rotation period of Mars 

Fig. 3. (a) Mariner 6 NE picture loca- 
tions, plotted on a painted globe of Mars. 
The first picture is taken with a blue filter. 
The camera-A filter sequence is blue. 

(camera A) frames and narrow-angle 
(camera B) frames alternate, (b) Mariner 
7 NE picture locations. The filter sequence 
is the same as for Mariner 6. 


considerably limited the possible longi- 
tudes of Mars that could effectively be 
viewed; in particular, the most promi- 
nent dark area, Syrtis Major, could not 
be seen under optimum conditions. 
Fortunately, Meridiani Sinus, a promi- 
nent dark area almost as strong and 
permanent as Syrtis Major, and various 
other important features well known 
from Earth observation, were easily 
accessible. . . . 

The cameras and other instruments 
were mounted on a two-axis "scan plat- 
form" which could be programmed to 
point the instruments in as many as five 
successive directions during the near- 
encounter. The particular orbit and 
platform-pointing strategy adopted for 
each spacecraft was designed to achieve 
the best possible return of scientific 
data within a context of substantial 
commonality but with some divergence 
of needs of the various experiments. 
The television experimenters placed 
great weight upon viewing a wide va- 
riety of classical features, including the 
polar cap; continuity of picture cover- 
age; substantial two-color overlap and 
some three-color overlap if possible; 
stereoscopic overlap; viewing the planet 
limb in blue light; viewing the same area 
at two different phase angles; and see- 
ing the same area under different view- 
ing conditions at nearly the same phase 
angle. . . . 

The Mariner 6 picture track was 
chosen to cover a broad longitude range 
at low latitudes in order to bring into 
view a number of well-studied transi- 
tional zones between light and dark 
areas, two "oases" (Juventae Fons and 
Oxia Palus). and a variable light re- 
gion (Deucalionis Regio). The picture 
track of Mariner 7 was selected so that 
it would cross that of Mariner 6 on the 
dark area Meridiani Sinus, thereby pro- 
viding views of that important region 
under different lighting conditions. The 
track was also specifically arranged to 
include the south polar cap and cap 
edge, to intersect the "wave-of-darken- 
ing" feature Hellespontus, and to cross 
the classical bright circular desert 

Camera Operation and 
Picture Appearance 

The first impression of Mars con- 
veyed by the pictures is that the surface 
is generally visible and is not obscured 
by clouds or haze except perhaps in 
the polar regions and in a few areas 
marked by the appearance of afternoon 
"clouds." The classical martian features 
stand out clearly in the far-encounter 
pictures, and, as the image grows, these 
features transform into areas having 
recognizable relationships to the num- 
erous craters which mark the surface. 
The near-encounter pictures seem to 
show a Moon-like terrain. However, 
one must bear in mind the fact that 
the camera system was designed to en- 
hance the contrast of local brightness 
fluctuations by a factor of 3, and that 
the contrast of the pictures is often 
further enhanced in printing. Actually, 
although the surface is generally visible, 
its contrast is much less than that of the 
moon under similar lighting conditions. 
Fewer shadows are seen near the ter- 

The determination of true surface 
contrast depends critically upon the 
amount of haze or veiling glare in the 
picture field. Although the pictures ap- 
pear to be free of such effects, more 
refined photometric measurements may 
well reveal the presence of veiling glare 
or a general atmospheric haze. Definite 
conclusions must await completion of 
the photometric reduction of the pic- 
tures, including corrections for vidicon 
dark current, residual images, shutter 
light leaks, and possible instrumental 

Observed Atmospheric Features 

Aerosol scattering. Clear-cut evidence 
for scattering layers in the atmosphere 
is provided by the pictures of the north- 
eastern limb of Mariner 7. The limb ap- 
pears in frames 7N1, 2, 3, 5, and 7, and 
in a few real-time digital A-camera 
frames received immediately prior to 
frame 7N 1 . . . . 


Mariners 6 and 7 Television Pictures; Preliminary Analysis 

The real-time digital data reveal an 
apparent limb haze near the south polar 
cap, and over the regions of Mare Ha- 
driaticum and Ausonia just east of Hel- 
las. The haze over these regions is not 
as bright as the haze discussed above, so 
it is unlikely that it is sufficiently dense 
to obscure surface features seen at NE 
viewing angles. A faint limb haze may 
also be present in the Mariner 6 limb 

The "blue haze." Despite these evi- 
dences of very thin aerosol hazes, visi- 
ble tangentially on the limb, there is no 
obscuring "blue haze" sufficient to ac- 
count for the normally poor visibility 
of dark surface features seen or photo- 
graphed in blue light and for their 
occasional better visibility — the so- 
called "blue-clearing" phenomenon (11, 

The suitability of the Mariner blue 
pictures for "blue haze" observations 
was tested by photographing Mars 
through one of the Mariner blue filters 
on Eastman III-G plates, whose response 
in this spectral region is similar to that 
of the vidicons used in the Mariner 
camera. Conventional blue photographs 
on unsensitized emulsions and green 
photographs were taken for comparison. 
A typical result is shown in Fig. 5; the 
simulated TV blue picture is very simi- 
lar to the conventional blue photographs. 

The blue pictures taken by Mariners 
6 and 7 clearly show craters and other 

surface features, even near the limb 
and terminator, where atmospheric ef- 
fects are strong. Polar cap frame 
7N17 shows sharp surface detail very 
near the terminator. The blue limb 
frame 6N1 shows surface detail corre- 
sponding to that seen in the subsequent 
overlapping green frame 6N3. Figure 
6 includes blue, green, and red pictures 
in the region of Sinus Meridiani. Al- 
though craters show clearly in all three 
colors, albedo variations, associated 
both with craters and with larger-scale 
features, are much more pronounced 
in green and red than in blue. Blue 
photographs obtained from the earth 
during the Mariner encounters show 
the normal "obscured" appearance of 

South polar cap shading. Another 
possible indication of atmospheric haze 
is the remarkable darkening of the 
south polar cap near both limb and 
terminator in the FE pictures (Fig. 7). 
This darkening is plainly not due to 
cloud or thick haze since, during near- 
encounter, surface features are clearly 
visible everywhere over the polar cap. 
It may be related to darkening seen in 
NE Mariner 7 frames near the polar 
cap terminator, and to the decrease in 
contrast with increasing viewing angle 
between the cap and the adjacent mare 
seen in frame 7N11 (Fig. 8b). The 
darkening may be due to optically thin 
aerosol scattering over the polar cap, 
or possibly to unusual photometric be- 
havior of the cap itself. In either case, 

Fig 5 Photographs of Mars from the earth, taken to compare Mariner-type blue-filter 
pictures with "standard" green and blue pictures of Mars. The pictures were taken 24 
May 1969 at New Mexico State University Observatory. (A) "Standard' blue 
(0915 U.T.); (B) Mariner blue (0905 U.T.): (C) standard green (0844 U.T.). North is at 
the top. 


it may be complicated by systematic 
diurnal or latitudinal effects. 

North polar phenomena. Marked 
changes seem to have occurred, between 
the flybys of Mariners 6 and 7, in the 
appearance of high northern latitudes. 
Some of these changes are revealed by 
a comparison of frames 6F34 and 7F73. 
which correspond to approximately the 
same central meridian and distance from 
Mars (Fig. 7). A large bright tongue 
(point 1 in frame 73) and a larger 
bright region near the limb (point 2) 
appear smaller and fainter in the Mari- 
ner 7 picture, despite the generally 
higher contrast of Mariner 7 FE frames. 
Much of the brightening near point 2 
has disappeared entirely between the 
two flybys; in fact, it was not visible at 
all on pictures taken by Mariner 7 
during the previous Mars rotation, al- 
though it was clearly visible in several 
Mariner 6 frames taken over the same 
range of distances. The bright tongue 
(point 1) increases in size and bright- 

ness during the martian day. as may be 
clearly seen from a comparison of 
frames 7F73 and 7F76 (Fig. 7). 

The widespread, diffuse brightening 
covering much of the north polar cap 
region (point 3) apparently corre- 
sponds to the "polar hood" which has 
been observed from the earth at this 
martian season (northern early au- 
tumn). The extent of this hood is small- 
er in Mariner 7 than in Mariner 6 
pictures: the region between, and just 
north of, points 1 and 2 appears to be 
covered by the hood in the Mariner 6 
frames, but shows no brightening in 
the Mariner 7 frames. 

The diffeient behaviors of the discrete 
bright regions and the hood suggest 
different origins for these features, al- 
though both apparently are either at- 
mospheric phenomena or else result 
from the interaction of the atmosphere 
and the surface. The discrete bright 
regions have fixed locations suggesting 
either surface frost or orographically 

Fig. 6. Composite of ten Mariner 6 pictures showing cratered terrain in the areas of Margaritifer Sinus (top left). Meridiani Sinus 
(top center), and Dcucalionis Regio (lower strip). Large-scale contrasts are suppressed by AGC and small-scale contrast is en- 
hanced (see text). Craters are clearly visible in blue frames 6N9 and 6N17. but albedo variations are subdued. Locations of three 
camera-B frames are marked by rectangles. North is approximated toward the top. and the sunset terminator lies near the right 
edge of 6N23. 


Mariners 6 and 7 Television Pictures; Preliminary Analysis 

fixed clouds. The fluctuation in the 
areal extent of the diffuse hood suggests 
cloud or haze. An extensive cloud or 
haze composed of either CO_. or CO. 
and H..O ice would be consistent with 

viewing of overlapping regions whose 
stereo angles lie between 5° and 12°. 
Little or no illumination is evident near 
and beyond the polar cap terminator. 
On the other hand, frames 7N11, 12, 

the atmospheric temperature structure 
revealed by the Mariner 6 occultation 
experiment (13) . . . . 

Search for local clouds and foi>. All 
NE frames from both spacecraft were 
carefully examined for evidences of 
clouds or fog. Away from the south 
polar cap there are no evidences of such 
atmospheric phenomena. Over the polar 
cap and near its edge a number of bright 
features which may be atmospheric can 
be seen, although no detectable shadows 
are present and no local differences in 
height can be detected by stereoscopic 

and 13 (Fig. 8) show several diffuse 
bright patches suggestive of clouds near 
the polar cap edge. Also, on the cap 
itself a few local diffuse bright patches 
are present in frames 7N15 (green) 
and 7N17 (blue). Unlike most polar 
cap craters, which appear sharp and 
clear, a few crater rims and other 
topographic forms appear diffuse 
(frames 7NI7, 18. and 19). In frames 
7N17 (blue) and 7N19 (green), 
remarkable curved, quasi-parallel bright 
streaks are visible near the south pole 
itself. While these show indications 

Fig. 7. Far-encounter pictures showing atmospheric and atmosphere-surface effects. 
Picture shutter times were as follows: 6F34, 30 July 0732 U.T.; 7F73, 4 August 1115 
U.T.; 7F76, 4 August 1336 U.T. 


of topographic form or control, includ- 
ing some crater-like shapes, their pos- 
sible cloud-like nature is suggested by 
lack of shading. . . . 

Observed Surface Features 

A primary objective of the Mariner 
6 and 7 television experiment was to 
examine, at close range, the principal 
types of martian surface features seen 
from the earth. 

Mariners 6 and 7, while confirming 
the earlier evidence of a Moon-like 
cratered appearance for much of the 
martian surface, have also revealed sig- 
nificantly different terrains suggestive of 
more active, and more recent, surface 
processes than were previously evident. 
Preliminary analyses indicate that at 
least three distinctive terrains are repre- 
sented in the pictures, as well as a mix- 
ture of permanent and transitory surface 
features displayed at the edge of, and 
within, the south polar cap; these ter- 
rains do not exhibit any simple correla- 
tion with the light and dark markings 
observed from the earth. 

Cratered terrains. Cratered terrains 
are those parts of the martian surface 
upon which craters are the dominant 
topographic form (Fig. 6). Pictures from 
Mariners 4, 6, and 7 all suggest that 
cratered terrains are widespread in the 
southern hemisphere. 

Knowledge of cratered terrains in the 
northern hemisphere is less complete. 
Cratered areas appear in some Mariner 
frames as far north as latitude 20°. Nix 
Olympica, which in far-encounter 
photographs appears to be an unusually 
large crater, lies at 18°N. Numerous 
craters are visible in the closer-range 
FE frames. These are almost exclusively 
seen in the dark areas lying in the 
southern hemisphere, few being visible 
in the northern hemisphere. This differ- 
ence may result from an enhancement 
of crater visibility by reflectivity varia- 
tions in dark areas. However, poor pho- 
tographic coverage, highly oblique 
views, and unfavorable sun angles com- 
bine to limit our knowledge of the 
northern portion of the planet. 

Preliminary measurements of the 
diameter-frequency distribution of mar- 
tian craters in the region Deucalionis 
Regio were made on frames 6N19 to 
6N22 and are shown in Fig. 9a. The 
curves are based upon 104 craters more 
than 0.7 kilometer in diameter seen on 
frames 6N20 and 22, and upon 256 
craters more than 7 kilometers in diam- 
eter seen on frames 6N19 and 21. The 
most significant result is the existence of 
two different crater distributions, a 
dichotomy also apparent in morphology. 
The two morphological crater types are 
(i) large and flat-bottomed and (ii) 
small and bowl-shaped. Flat-bottomed 
craters are most evident on frames 
6N19 and 6N21. The diameters range 
from a few kilometers to a few hundred 
kilometers, with estimated diameter-to- 
depth ratios on the order of 100 to 1. 
The smaller, bowl-shaped craters are 
best observed in frames 6N20 and 
6N22 and resemble lunar primary- 
impact craters. Some of them appear to 
have interior slopes steeper than 20 
degrees .... 

On frame 6N20 there are low irregu- 
lar ridges similar to those seen on the 
lunar maria. However, no straight or 
sinuous rills have been identified with 
confidence. Similarly, no Earth-like tec- 
tonic forms possibly associated with 
mountain building, island-arc formation, 
or compressional deformation have been 

Chaotic terrains. Mariner frames 
6N6, 14, and 8 (Fig. 10a) show two 
types of terrain — a relatively smooth 
cratered surface that gives way abruptly 
to irregularly shaped, apparently lower 
areas of chaotically jumbled ridges. 
This chaotic terrain seems characteris- 
tically to display higher albedo than its 
surroundings. On that basis, we infer 
that significant parts of the overlapping 
frames 6N5, 7, and 15 may contain 
similar terrain, although their resolution 
is not great enough to reveal the general 
morphological characteristics. As shown 
in Fig. 10a, frames 6N6, 14, and 8 all 
lie within frame 6N7, for which an 
interpretive map of possible chaotic ter- 
rain extent has been prepared (Fig. 11). 


Mariners 6 and 7 Television Pictures; Preliminary Analysis 


Fig. 8. (a) Composite of polar cap frames 7N10 to 7N20. Effects of AGC are clearly evident near the terminator (right) and at 
cap edge, (b) Composite of poplar cap camera- A frames 7N11 to 7N19. The effects of AGC have been partially corrected, but con- 
trast is enhanced. The south pole lies near the parallel streaks in the lower right corner of frame 7N17. 

About 10 G square kilometers of cha- 
otic terrain may lie within the strip, 
1000 kilometers wide and 2000 kilo- 
meters long, covered by these Mariner 
6 wide-angle frames. Frames 6N9 and 
10 contain faint suggestions of similar 
features. This belt lies at about 20°S, 
principally within the poorly defined, 
mixed light-and-dark area between the 
dark areas Aurorae Sinus and Marga- 
ritifer Sinus. 

Chaotic terrain consists of a highly 
irregular plexus of short ridges and de- 
pressions, 1 to 3 kilometers wide and 2 

to 10 kilometers long, best seen in 
frame 6N6 (Fig. 10a). Although irregu- 
larly jumbled, this terrain is different in 
setting and pattern from crater ejecta 
sheets. Chaotic terrain is practically 
uncratered; only three faint possible 
craters are recognized in the 10 G -square- 
kilometer area. The patches of chaotic 
terrain are not all integrated, but they 
constitute an irregular pattern with an 
apparent N to N 30°E grain. 

Featureless terrains. The floor of the 
bright circular "desert," Hellas, cen- 
tered at about 40°S, is the largest area 


of featureless terrain so far identified. 
Even under very low solar illumination 
the area appears devoid of craters down 
to the resolution limit of about 300 
meters. No area of comparable size and 
smoothness is known on the moon. It 
may be that all bright circular "deserts" 
of Mars have smooth featureless floors; 
however, in the present state of our 
knowledge it is not possible to define 
any significant geographic relationship 
for featureless terrains. . . . 

South polar cap features. The edge of 
the martian south polar cap was visible 
at close range over a 90° span of longi- 
tude, from 290 °E to 20 °E, and the cap 
itself was seen over a latitude range 
from its edge, at -60°, southward to, 
and perhaps beyond, the pole itself. 
Solar zenith angles ranged from 51° to 
90° and more; the terminator is clearly 
visible in one picture. The phase angle 
for the picture centers was 35°. The 
superficial appearance is that of a 
clearly visible, moderately cratered sur- 
face covered with a varying thickness of 
"snow." The viewing angle and the un- 
familiar surface conditions make quan- 
titative comparison with other areas of 
Mars difficult with respect to the num- 
ber and size distributions of craters. 
Discussion here is therefore confined to 
those qualitative aspects of the polar 
cap which seem distinctive to that 

The edge of the cap was observed in 
the FE pictures to be very nearly at 
60°S, as predicted from Lowell Observ- 
atory measurements (15); this lends 
confidence to Earth-based observations 
concerning the past behavior of the 
polar caps. 

The principal effect seen at the cap 
edge is a spectacular enhancement of 
crater visibility and the subtle appear- 
ance of other topographic forms. In 
frames 7N11 to 7N13, where the local 
solar zenith angle was about 53°, craters 
are visible both on and off the cap. How- 
ever, in the transition zone, about 2 
degrees of latitude in width, the popu- 
lation density of visible craters is sev- 
eral times greater, and may equal any 
so far seen on Mars. This enhancement 

of crater visibility results mostly from 
the tendency, noted in Mariner 4 pic- 
tures 14 and 15, for snow to lie prefer- 
entially on poleward-facing slopes. 

In frame 7N12 the cap edge is seen 
in finer detail. The tendency mentioned 
above is here so marked as to cause con- 
fusion concerning the direction of the 
illumination. There are several tiny 
craters as small as 0.7 kilometer in di- 
ameter, and areas of fine mottling and 
sinuous lineations are seen near the 
larger craters. The largest crater shows 
interesting grooved structure, near its 
center and on its west inner wall, which 
appears similar to that in frame 6N18. 

On the cap itself, the wide-angle views 
show many distinct reflectivity varia- 
tions, mostly related to moderately large 
craters but not necessarily resulting 
from slope-illumination effects. Often a 
crater appears to have a darkened floor 
and a bright rim, and in some craters 
having central peaks the peaks seem un- 
usually prominent. In frames 7N17 and 
7N19 several large craters seem to have 
quite dark floors. 

i — i i i i in 


~\ I I I l l l 



'Ol I i i i I 

2 3 4 S 6 8 10 20 30 40 60 100 

Fig. 9. (a) Preliminary cumulative distri- 
bution of crater diameters. Solid curve at 
right is based upon 256 counted craters in 
frames 6N19 and 6N21 having diameters 
> 7 kilometers. The solid curve at left is 
based upon 104 counted craters in frames 
6N20 and 6N22. The error bars are from 
counting statistics only (N'). 


In contrast, the high-resolution polar 
cap frames 7N14 to 7N20 suggest a 
more uniformly coated surface whose 
brightness variations are mostly due to 
the effects of illumination upon local 
relief. . . . 

Some of the classical "oases" ob- 
served from the earth have now been 
identified with single, large, dark-floored 
craters (such as Juventae Fons. see 4 
and Fig. 4) or groups of such craters 
(such as Oxia Palus, frame 7N5). At 
least two classical "canals" (Cantabras 
and Gehon) have been found to coincide 
with quasi-linear alignment of several 
dark-floored craters, shown also in 
frame 7N5 (Fig. 13). As reported else- 
where (4), other canals are composed of 
irregular dark patches. It is probable 
that most canals will, upon closer in- 
spection, prove to be associated with a 
variety of physiographic features, and 
that eventually they will be considered 
less distinctive as a class. . . . 

Mariners 6 and 7 Television Pictures; Preliminary Analysis 
Inferences concerning Processes 
and Surface History 

The features observed in the Mariner 
6 and 7 pictures are the result of both 
present and past processes; therefore, 
they provide the basis of at least limited 
conjecture about those processes and 
their variations through time. In this 
section we consider the implications of 
(i) the absence of Earth-like tectonic 
features; (ii) the erosion, blanketing, 
and secondary modification evidenced in 
the three principal terrains; and (iii) 
the probable role of equilibrium be- 
tween CO., solid and vapor in the for- 
mation of features of the south polar 
cap. We also consider the possible role 
of equilibrium between HO solid and 
vapor as an explanation of the diurnal 
brightenings observed in the FE photo- 
graphs and biological implications. 

Significance of the absence of Earth- 
like forms. The absence of Earth-like 

■ 4f 

• ' . 





6N14 J 


319° E 



V:. •••::•) Y.:-\&V- 



342.4° E 


• V 

M 6NI4 


i u.; 










312° E 


1 1 


1 , 1 





336.3° E 

Approximate East -West center scale (km) 
Fig. 11. Interpretive drawing showing the possible extent of chaotic terrain in frame 6N7. 

tectonic features on Mars indicates 
that, for the time period represented by 
the present large martian topographic 
forms, the crust of Mars has not been 
subjected to the kinds of internal forces 
that have modified, and continue to 
modify, the surface of the earth. 

Inasmuch as the larger craters prob- 
ably have survived from a very early 
time in the planet's history, it is in- 
ferred that Mars's interior is, and prob- 
ably has always been, much less active 
than the earth's (79). Furthermore, 
a currently held view (20) is that the 
earth's dense, aqueous atmosphere may 
have formed early, in a singular event 
associated with planetary differentiation 
and the origin of the core. To the ex- 
tent, therefore, that surface tectonic 
features may be related in origin to the 
formation of a dense atmosphere, their 
absence on Mars independently suggests 
that Mars never had an Earth-like at- 

Age implications of cratered terrains. 
At present, the ages of martian topo- 
graphic forms can be discussed only by 
comparison with the moon. Both the 
moon and Mars exhibit heavily cratered 
and lightly cratered areas, which evi- 
dently reflect in each case regional dif- 
ferences in the history of, or the re- 
sponse to, meteoroidal bombardment 
over the total life-span of the surfaces. 
The existence of a thin atmosphere on 
Mars may have produced recognizable 
secondary effects in the form and size 
distribution of craters, by contrast with 
the moon, where a significant atmo- 
sphere has presumably never been 
present. To the extent that relative 
fluxes of large objects impinging upon 
the two bodies can be determined, or 
a common episodic history established, 
a valid age comparison may be hoped 
for, except in the extreme case of a 
saturated cratered surface, where only 
a lower limit to an age can be found. 



It is a generally accepted view that 
the present crater density on the lunar 
uplands could not have been produced 
within the 4.5-billion-year age of the 
solar system had the bombardment rate 
been no greater than the estimated 
present rate; that is, the inferred mini- 
mum age is already much greater than 
is considered possible. Indeed, it is 
found that even the sparsely cratered 
lunar maria would have required about 
a billion years to attain their present 
crater density. Unless this discrepancy 
is somehow removed by direct measure- 
ments of the crystallization ages of re- 
turned samples of lunar upland and 
mare materials, the previously accepted 
implication of an early era of high 
bombardment followed by a long pe- 
riod of bombardment at a drastically 
reduced rate will presumably stand. 

In the case of Mars, a bombardment 
rate per unit area as much as 25 times 
that on the moon has been estimated 
(27). However, even this would still 
seem to require at least several billion 
years to produce the density of large 
craters that is seen on Mars in the more 
heavily cratered areas (19). Thus these 
areas could also be primordial. Further, 
were these areas to have actually been 
bombarded at a constant rate for such 
a time, at least a few very recent, large 
craters should be visible, including sec- 
ondary craters and other local effects. 
Instead, the most heavily cratered areas 
seem relatively uniform with respect 
to the degree of preservation of large 
craters, with no martian Tycho or Co- 
pernicus standing out from the rest. This 
again suggests an early episodic history 
rather than a continuous history for 
cratered martian terrain, and increases 
the likelihood that cratered terrain is 

If areas of primordial terrain do 
exist on Mars, an important conclusion 
follows: these areas have never been 
subject to erosion by water. This in 
turn reduces the likelihood that a dense, 
Earth-like atmosphere and large, open 
bodies of water were ever present on 
the planet, because these would almost 
surely have produced high rates of 

6 and 7 Television Pictures; Preliminary Analysis 

planet-wide erosion. On the earth, no 
topographic form survives as long as 
10 8 years unless it is renewed by up- 
lift or other tectonic activity. 

Implications of modification of ter- 
rain. Although erosional and blanketing 
processes on Mars have not been strong 
enough to obliterate large craters within 
the cratered terrains, their effects are 
easily seen. On frames 6N19 and 6N21 
(Fig. 6), even craters as large as 20 to 
50 kilometers in diameter appear scarce 
by comparison with the lunar uplands 
[a feature originally noted by Hartmann 
(19) on the basis of the Mariner 4 
data], and the scarcity of smaller cra- 
ters is marked. The latter have a rel- 
atively fresh appearance, however, 
which suggests an episodic history of 
formation, modification, or both. Such 
a history seems particularly indicated 
by the apparently bimodal crater fre- 
quency distribution of Fig. 9. 

Marked erosion, blanketing, and 
other surface processes must have been 
operating almost up to the present in 
the areas of featureless and chaotic ter- 
rains; only this could account for the 
absence of even small craters there. 
These processes may not be the same 
as those at work on the cratered ter- 
rains, because large craters have also 
been erased. The cratered terrains ob- 
viously have never been affected by such 
processes; this indicates an enduring 
geographic dependence of these extraor- 
dinary surface processes. 

The chaotic terrain gives a general 
impression of collapse structures, sug- 
gesting the possibility of large-scale 
withdrawal of substances from the un- 
derlying layers. The possibility of per- 
mafrost some kilometers thick, and of 
its localized withdrawal, may deserve 
further consideration. Magmatic with- 
drawal or other near-surface disturb- 
ance associated with regional volcanism 
might be another possibility, but the 
apparent absence of extensive volcanic 
terrains on the surface would seem to 
be a serious obstacle to such an inter- 
pretation. It may also be that chaotic 
terrain is the product either of some 
unknown intense and localized ero- 


Fig. 10. (a) Examples of chaotic terrain. The approximate locations of the camera-B views inside camera-A frame 6N7 are shown 
by the dashed rectangles. North is approximately at the top. (b) Example of possible chaotic terrrin. The lighter color and the 
absence of craters suggest that large parts of the right-hand half of this camera-A view may consist of chaotic terrain, (c) Example 
of chaotic terrain. The location of frame 6N14 inside frame 6N15 is shown by the solid rectangle. 



sional process or of unsuspected local 
sensitivity to a widespread process. 

Carbon dioxide condensation effects. 
The Mariner 7 NE pictures of the polar 
cap give no direct information concern- 
ing the material or the thickness of the 
polar snow deposit, since the observed 
brightness could be produced by a very 
few milligrams per square centimeter 
of any white, powdery material. How- 
ever, they do provide important indirect 
evidence as to the thickness of the de- 
posit and, together with other known 
factors, may help to establish its com- 

The relatively normal appearance of 
craters on the polar cap in the high- 
resolution frames, and the existence on 
these same frames of topographic relief 
unlike that so far recognized elsewhere 
on the planet, suggest that some of the 
apparent relief may be due to variable 
thicknesses of snow, perhaps drifted by 
wind. If it is, local thicknesses of at 
least several meters are indicated. 

The structure of the polar cap edge 
shows that evaporation of the snow is 
strongly influenced by local slopes — 
that is, by insolation effects rather than 
by wind. On the assumption that the 
evaporation is entirely determined by 
the midday radiation balance, when the 
absorbed solar power exceeds the ra- 
diation loss at the appropriate frost- 
point temperature, one may estimate the 
daily evaporation loss from the cap. We 
find the net daily loss to be about 0.8 
gram per square centimeter in the case 
of CO,, although the loss is reduced by 
overnight recondensation. In the case 
of H.O, the loss would be about 0.08 
gram per square centimeter, and it 
would be essentially irreversible because 
H.O is a minor constituent whose de- 
position is limited by diffusion. 

Since the complete evaporation of 
the cap at a given latitude requires 
many days, we may multiply the above 
rates by a factor between 10 and 100, 
obtaining estimates for total cap thick- 
ness of tens of grams per square centi- 
meter for CO. and several grams per 
square centimeter for H.O, on the as- 
sumption that the cap is composed of 

6 and 7 Television Pictures; Preliminary Analysis 

one or the other of these materials. The 
estimate for CO L . is quite acceptable, but 
that for H.O is unacceptable because of 
the problem of transporting such quan- 
tities annually from one pole to the 
other at the observed vapor density 
(22). For the remainder of this dis- 
cussion we assume the polar cap to be 
composed of CO.. with a few milli- 
grams of H.O per square centimeter 
deposited throughout the layer. 

Several formations have been ob- 
served which suggest a tendency for 
snow to be preferentially removed from 
low areas and deposited on high areas, 
contrary to what might be expected 
under quiescent conditions (23). These 
formations include craters with dark 
floors and bright rims, prominent cen- 
tral peaks in some craters, and irregu- 
lar depressed areas (frames 7N14, 15, 
and 17). While such effects might result 
simply from wind transport of solid 
material, it is also possible that inter- 
change of solid and vapor plays a role. 

Water: processes suggested by bright- 
ening phenomena. Several of the bright- 
ening and haze phenomena described 
above could be related either to forma- 
tion of H 2 frost on the surface or to 
formation of H.O ice clouds in the 
atmosphere. In most of these instances, 
however, the phenomena could equally 
well be explained by condensation of 
CO.. This is true of the bright tongues 
and polar hood in the north polar re- 
gion, of the cloud-like features observed 
over and near the south polar cap, and 
of the limb hazes observed in tropical 
latitudes and over the Mare Hadriati- 
cum and Ausonia regions. 

On the other hand, the brightenings 
in the Nix Olympica, Tharsis, Candor, 
and Tractus Albus regions cannot be 
explained by CO. condensation be- 
cause their complete topographic con- 
trol requires that they be on or near the 
surfaces where temperatures are well 
above the CO. frost point. An explana- 
tion of these phenomena in terms of 
H.O condensation processes also faces 
serious difficulties, however. Most of 
the region is observed to brighten dur- 


ing the forenoon, when the surface is 
hotter than either the material below 
or the atmosphere above, so that water 
vapor could not diffuse toward the sur- 
face and condense on it, either from 
above or below. Thus a surface ice-frost 
is very unlikely. A few features in the 
area, parts of the "W-cloud," for ex- 
ample, are observed to brighten mark- 
edly during the late afternoon, where 
H.O frost could form on the surface if 
the air were sufficiently saturated. These 
features are not observed, from the 
earth, to be bright in the early morning, 
but a thin layer of H.O frost persisting 
through the night would evaporate al- 
most immediately when illuminated by 
the early morning sun, provided the air 
were then sufficiently dry. Under these 
conditions, the behavior of the "W- 
cloud" could be due to frost. 

The diurnal behavior of the bright 
regions throughout this part of Mars 
is consistent with a theory of convective 
H 2 ice clouds, but the absence of any 
cloud-like morphology and the clear to- 
pographic detail observed at the high- 
est resolution available (frame 7F76) 
render this explanation questionable. 
Even very light winds of 5 meters per 
second would produce easily observable 
displacements of the order of 100 kilo- 
meters in the course of the more than 
one-fourth of the Mars day during 
which these regions were continuously 
observed by each spacecraft. Since con- 
densation and evaporation processes are 
slow at Mars temperatures and pres- 
sures, some observable distortion and 
streakiness due to these displacements 
should be seen in clouds, even if they 
are orographically produced. No such 
distortions or streakiness are observed. 
An additional difficulty with an ex- 
planation of these phenomena in terms 
of H.O condensation lies in the rela- 
tively rapid removal of water from 
the local surface. Water vapor evolved 
from the surface during the daytime 
would quickly be transported upward 
through a deep atmospheric layer by 
thermal convection, and most of it 
would be removed from the source re- 

gion. Local permafrost sources should 
be effectively exhausted by this mecha- 
nism within a few hundred years at 
most, unless somehow replenished. Since 
most of this region lies near the equator, 
where seasonal temperature variations 
are small, it is difficult to see how any 
significant seasonal replenishment from 
the atmosphere could take place. The 
possibility of replenishment from a sub- 
surface source of liquid water is not. 
considered here. 

In summary, in our examination of 
the data thus far, we see no strong in- 
dications of H.O processes involving 
vapor and ice. The brightenings seen 
in the tropics and subtropics at far-en- 
counter are not easily explained by a 
mechanism involving H..O. On the other 
hand, we have no satisfactory alterna- 
tive explanation for these phenomena. 
Perhaps detailed exploration of these 
regions by the Mariner '71 orbiters will 
provide the answer. 

Biological inferences. No direct evi- 
dence suggesting the presence of life on 
Mars has been found in the pictures. 
This is not surprising, since martian life, 
if any, would probably be microbial and 
undetectable at a resolution of 300 
meters. Although inconclusive on the 
question of martian life, the photographs 
are informative on at least three sub- 
jects of biological interest: the general 
nature of the martian maria, the present 
availability of water, and the availabil- 
ity of water in the past. 

One of the most surprising results 
so far of the TV experiment is that 
nothing in the pictures suggests that 
the dark areas, the sites of the sea- 
sonal darkening wave, are more favor- 
able for life than other parts of the 
planet. On the contrary, it would now 
appear that the large-scale surface 
processes implied by the chaotic and 
featureless terrains may be of greater 
biological interest than the wave of 
darkening. We reiterate that these are 
preliminary conclusions: it may be that 
subtle physiographic differences be- 
tween dark and bright regions will 
become evident when photometrically 


corrected pictures are examined. 

With regard to the availability of 
water, the pictures so far have not re- 
vealed any evidence of geothermal areas. 
We would expect such areas to be per- 
manently covered with clouds and frost, 
and these ought to be visible on the 
morning terminator: no such areas have 
been seen. A classically described 
feature of the polar cap which has been 
interpreted as wet ground — the dark 
collar — has likewise not been found. 
Other locales which have been consid- 
ered to be sites of higher-than-average 
moisture content are those which show 
diurnal brightening. A number of such 
places have been observed in the pic- 
tures, but on close inspection the bright- 
ening appears not to be readily inter- 
pretable in terms of water frosts or 
clouds. Pending their definite identifi- 
cation, however, the brightenings 
should be considered possible indica- 
tions of water. 

The results thus reinforce the conclu- 
sion, drawn from Mariner 4 and ground- 
based observations, that scarcity of 
water is the most serious limiting factor 
for life on Mars. No terrestrial species 
known to us could live in the dry mar- 
tian environment. If there is a perma- 
frost layer near the surface, or if the 
small amount of atmospheric water 
vapor condenses as frost in favorable 
sites, it is conceivable that, by evolu- 
tionary adaptation, life as we know it 
could use this water and survive on the 
planet. In any case, the continued 
search for regions of water condensa- 
tion on Mars will be an important task 
for the 1971 orbiter. 

The past history of water on Mars is 
a matter of much biological interest. 
According to current views, the chemi- 
cal reactions which led to the origin of 
life on the earth were initiated in the 
reducing atmosphere of the primitive 
earth. These reactions produced simple 
organic compounds which were precipi- 
tated into the ocean, where they under- 
went further reactions that eventually 
yielded living matter. The pictorial evi- 
dence raises the question of whether 

Mariners 6 and 7 Television Pictures; Preliminary Analysis 

Mars ever had enough water to sustain 
an origin of life. If the proportion of 
water outgassed relative to C0 2 is the 
same for Mars as for the earth, then, 
from the mass of CO L > now in the mar- 
tian atmosphere, it can be estimated that 
Mars has produced sufficient water to 
cover the planet to a depth of a few 
meters. The question is whether any- 
thing approaching this quantity of water 
was ever present on Mars in the liquid 

The existence of cratered terrains 
and the absence of Earth-like tectonic 
forms on Mars clearly implies that the 
planet has not had oceans of terrestrial 
magnitude for a very long time, pos- 
sibly never. However, we have only 
very rough ideas of how much ocean is 
required for an origin of life, and of 
how long such an ocean must last. An 
upper limit on the required time, based 
on terrestrial experience, can be derived 
from the age of the oldest fossils, >3.2 
x 10° years (24). Since these fossils are 
the remains of what were apparently 
highly evolved microorganisms, the ori- 
gin of life must have taken place at a 
much earlier time, probably during the 
first few hundred million years of the 
earth's history. While one cannot rule 
out, on the basis of the TV data, the 
possibility that a comparably brief, 
aqueous epoch occurred during the 
early history of the planet, it must be 
said that the effect of the TV results 
so far is to diminish the a priori likeli- 
hood of finding life on Mars. However, 
it should be noted that if Mars is to be 
a testing ground for our notions about 
the origin of life, we must avoid using 
these same notions to disprove in ad- 
vance the possibility of life on that 

Potentialities of the Data 

Careful computer restoration ot the 
pictures, starting with data recovered 
from six sequential playbacks of the 
near-encounter analog tapes, will be 
carried out over the next several months. 
This further processing will greatly en- 


hance the completeness, appearance, 
and quantitative usefulness of the pic- 
tures. While it is not yet certain whether 
the desired 8-bit relative photometric 
accuracy can be attained, there are 
reasonable grounds for thinking that 
much new information bearing on the 
physiography, meteorology, geography, 
and other aspects of Mars will ultimately 
be obtained from the pictures. Some of 
the planned uses of the processed data 
are as follows. 

Stereoscopy. Most of the NE wide- 
angle pictures contain regions of two- 
picture overlap, and a few contain 
regions of three-picture overlap. These 
areas can be viewed in stereoscopic vi- 
sion in the conventional manner of aer- 
ial photography. Preliminary tests on 
pictures of the south polar cap (frames 
7N17 and 7N19) indicate that measure- 
ment of crater depth, central-peak 
height, and crater-rim height is possible. 
However, accuracy can be estimated 
for the elevation determinations at this 

Planetary radii. Geometric correction 
of the FE photographs should make it 
possible to determine the radius of 
Mars as a function of latitude, and 
possibly of longitude. The geometric 
figure of Mars has been historically 
troublesome because of inconsistencies 
between the optical and the dynamical 
oblateness, a discrepancy amounting to 
some 18 kilometers in the value for the 
difference of the equatorial and polar 
radii. It is possible that the darkening 
of the polar limb observed by Mariners 
6 and 7, if it is a persistent phenomenon, 
might have systematically affected the 
earlier telescopic measurements of the 
polar diameter more than irradiation 
has, giving too large a value for the 
optical flattening. However, this cannot 
explain the large flattening obtained 
from surface-feature geodesy (25). Al- 
though a fairly reliable figure for the 
polar flattening may be obtained from 
the Mariner data, it is unlikely that the 
actual radii will be determined with an 
accuracy greater than several kilometers 
because of the relatively low picture- 

element resolution in these frames and 
the difficulty in locating the limb. 

Cartography. The large number of 
craters found on the surface of Mars 
makes it feasible to establish a control 
net which uses topographic features as 
control points, instead of surface mark- 
ings based on albedo differences. This 
net should provide the basic locations 
for compiling a new series of Mars 
charts. The NE pictures, which cover 
10 to 20 percent of the area of the 
planet, will constitute the basic material 
for detailed maps of these areas. 

Satellites. We hope to detect the 
larger of Mars's satellites, Phobos, in 
two of the Mariner 6 FE pictures taken 
when Phobos was just beyond the limb 
of the planet. The satellite should have 
moved between the two frames by about 
ten picture elements, and should appear 
as a "defect" that has moved by this 
amount between the two pictures. If 
Phobos itself is not visible, its shadow 
(again detectable by its motion) should 
be. The shadow will be some five pic- 
ture elements across and will have a 
photometric depth of about 10 percent. 
If the photometric depth of the shadow 
can be measured accurately, we can de- 
termine the projected area (and hence 
the diameter) of the satellite. A similar 
method has been used to measure the 
diameter of Mercury during solar tran- 

Photometric studies. We expect to 
derive the photometric function for each 
color, combining data from the two 
spacecraft. Observations by the current 
Mariners were made near 25°, 35°. 45°, 
and 80° phase. Since data obtained 
from the earth can be used to establish 
the absolute calibration at the smaller 
phase angles, we will also be able to 
relate the 80°-phase data to Earth-based 
observations, thus doubling the range 
over which the phase function is deter- 
mined. This information should then 
make possible the determination of 
crater slopes. Agreement for areas of 
overlap between different filters and 
between A-camera and B-camera frames 
can be used to check the validity of the 



results and possibly to measure and 
correct for atmospheric scattering. 

The reciprocity principle may be use- 
ful in testing quantitatively for diurnal 
changes in the FE pictures. Such 
changes might include dissipation of 
frost or haze near the morning ter- 
minator and formation of afternoon 
clouds near the limb. 

Overlap areas in NE pictures can be 
used to obtain approximate colors, even 
though these areas are seen at different 
phase angles in each color. In addition, 
color-difference or color-ratio pictures 
may be useful in identifying local areas 
of anomalous photometric or colori- 
metric behavior. Camera-A digital pic- 
tures obtained by Mariner 7 in late 
far-encounter will be very useful for 
making color measurements. 

Comparison of pictures with radar- 
scattering and height data. The reflec- 
tion coefficient of the martian surface 
for radar waves of decimeter wavelength 
shows marked variations at a given 
latitude as a function of longitude. Even 
though few of the areas of Mars so far 
observed by radar are visible at close 
range, some correlation of topography 
with radar reflectivity may become ap- 
parent upon careful study. Clearly, the 
Mariner pictures will become steadily 
more valuable in this connection as 
more radar results and other height 
data become available. 

Effects on Mariner '71 

The distinctive new terrains revealed 
in the Mariner 6 and 7 pictures, the 
relatively small fraction (10 to 20 per- 
cent) of the surface so far viewed even 
at moderate (A-camera) resolution, and 
the tantalizing new evidence of after- 
noon-brightening phenomena all empha- 
size the importance of an exploratory, 
adaptive strategy in 1971 as opposed to 
a routine mapping of geographic fea- 
tures. The fact that each of three suc- 
cessive Mariner spacecraft has revealed 
a new and unexpected topography 
strongly suggests that more surprises 
(perhaps the most important ones) are 
still to appear. 

6 and 7 Television Pictures; Preliminary Analysis 

A primary objective should be to view 
nearly all of the visible surface at A- 
camera resolution (1-kilometer pixel 
spacing), and to inspect selected typical 
areas at higher resolution, very early in 
the 90-day orbiting period. The true ex- 
tent and character of cratered, chaotic, 
and featureless terrains, and of any new 
kinds of terrain, can thus be deter- 
mined and correlated with classical light 
and dark areas, with regional height 
data, and so on. 

A second objective should be to 
search for and examine, in both spatial 
and temporal detail, those areas which 
suggest the local presence of water, 
through the afternoon-brightening phe- 
nomena, morning frosts or fogs, or other 
behavior not now recognized. Certainly 
the known "W-cloud" areas, Nix Olym- 
pica, and other, similar areas known 
from Earth observation take on a new 
interest by virtue of the Mariner 6 and 
7 results. 

The complex structure found in the 
south polar cap calls for further exam- 
ination, particularly with respect to 
separation of its more permanent fea- 
tures from diurnally or seasonally vary- 
ing ones. The sublimation of the cap 
should be carefully followed, so as to 
detect evidence of variations in thick- 
ness of the deposit and especially evi- 
dence of the possible existence of per- 
manent deposits. Study of the north 
polar cap at close range should also be 
exceedingly interesting. 

Effects on Viking '73 

If the effects of the Mariner 6 and 7 
results on Mariner '71 are substantial, 
they at least do not require a change of 
instrumentation, only one of mission 
strategy. This may not be true of the 
effects on Viking '73. The discovery of 
so many new, unexpected properties of 
the martian surface and atmosphere 
adds a new dimension to the problem of 
selecting the most suitable landing site 
and may make Viking even more de- 
pendent on the success of Mariner '71 
than has been supposed. Furthermore, 
since so much new information is re- 


vealed through the tenfold step in reso- 
lution afforded by the B-camera frames, 
a further substantial increase in resolu- 
tion, not available to Mariner '71, may 
have to be incorporated in Viking in 
order to examine even more closely the 
fine-scale characteristics of various ter- 
rain types before a landing site is 

Summary and Conclusions 

Even in relatively unprocessed form, 
the Mariner 6 and 7 pictures provide 
fundamental new insights concerning 
the surface and atmosphere of Mars. 
Several unexpected results emphasize 
the importance of versatility in instru- 
ment design, flexibility in mission de- 
sign, and use of an adaptive strategy in 
exploring planetary surfaces at high 

The surface is clearly visible in all 
wavelengths used, including the blue. 
No blue-absorbing haze is found. 

Thin, patchy, aerosol-scattering lay- 
ers are present in the atmosphere at 
heights of from 15 to 40 kilometers, at 
several latitudes. 

Diurnal brightening in the "W-cloud" 
area is seen repeatedly and is associated 
with specific topographic features. No 
fully satisfactory explanation for the 
effect is found. 

Darkening of the polar cap in a band 
near the limb is clearly seen in FE pic- 
tures and is less distinctly visible in one 
or two NE frames. Localized, diffuse 
bright patches are seen in several places 
on and near the polar cap; these may be 
small, low clouds. 

Widespread cratered terrain is seen, 
especially in dark areas of the southern 
hemisphere. Details of light-dark transi- 
tions are often related to local crater 
forms. Asymmetric markings are char- 
acteristic of craters in many dark areas; 
locally, these asymmetries often appear 
related, as if defined by a prevailing 
wind direction. 

Two distinct populations of primary 
craters are present, distinguished on the 
basis of size, morphology, and age. An 
episodic surface history is indicated. 
In addition to the cratered terrain 
anticipated from Mariner 4 results, at 
least two new, distinctive topographic 
forms are seen: chaotic terrains and 
featureless terrains. The cratered terrain 
is indicative of extreme age; the two new 
terrains both seem to require the present- 
day operation of especially active modi- 
fying processes in these areas. When 
seen at closer range, the very bright, 
streaked complex found in the Tharsis- 
Candor region may reveal yet another 
distinctive topographic character. Be- 
cause of the afternoon-brightening phe- 
nomena long known here, this area pro- 
vides a fascinating prospect for further 
exploration in 1971. 

No tectonic and topographic forms 
similar to terrestrial forms are observed. 
Evidences of both atmosphere-surface 
effects and topographic effects are seen 
on the south polar cap. At the cap edge, 
where the "snow" is thinnest, strong 
control by solar heating, as affected by 
local slopes, is indicated. Crater visibil- 
ity is greatly enhanced in this area. 

On the cap itself, intensity variations 
suggestive of variable "snow" thickness 
are seen. These may be caused by wind- 
drifting of the snow or by differential 
exchange of solid and vapor, or by both. 
Snow thicknesses here of several 
grams or several tens of grams per 
square centimeter are inferred if the 
snow material is K.O or CO., respec- 
tively. The possibility that the material 
is H l .O seems strongly ruled out on 
several grounds. 

Variable atmospheric, and atmo- 
sphere-surface, effects are seen at high 
northern latitudes; these effects include 
the polar "hood" and bright, diurnally 
variable circumpolar patches. 

Several classical features have been 
successfully identified with specific topo- 
graphic forms, mostly craters or crater 


Mariners 6 and 7 Television Pictures; Preliminary Analysis 

The findings are inconclusive on the 
question of life on Mars, but they are 
relevant in several ways. They support 
earlier evidence that scarcity of water, 
past and present, is a serious limiting 

factor for life on the planet. Nothing so 
far seen in the pictures suggests that 
the dark regions are more favorable for 
life than other parts of Mars. 

References and Notes 

R. B. Leighton, B. C. Murray, R. P. Sharp, 
J. D. Allen, R. K. Sloan, Science 149, 627 

, "Mariner IV Pictures of Mars," Tech. 

Rep. Jet Propul. Lab. Calif. Inst. Technol. 
No. 32-884 (1967), pt. 1. 

R. B. Leighton, N. H. Horowitz, B. C. Mur- 
ray, R. P. Sharp, A. G. Hcrriman, A. T. 
Young, B. A. Smith, M. E. Davies, C. B. 
Leovy, Science 165. 684 (1969). 

, ibid., p. 787. 

The 1/7 digital TV data for the central 20 
percent of each line were replaced by en- 
coded data from other on-board experiments. 
In this region, coarser. 1 '28 digital data (6- 
bit-encoded for every 28th pixel), stored on 
the analog tape recorder, were available (see 
Fig. 2). 

D. G. Montgomery, in preparation. 

This procedure is semiautomatic, subject to 
hand correction by the computer operator as 
. G. E. Danielson. in preparation. 
For each spacecraft, this must be done for 
each filter of each camera and for all cali- 
bration temperatures, and the results must 
be corrected to the observed flight tem- 

Most of the real-time FE A-camera digital 
pictures were of no value because little or 
none of the image projected outside the 
central 20 percent blank area. 

E. C. Slipher, Publ. Astron. Soc. Pacific 49, 
137 (1937). 

J. B. Pollack and C. Sagan, Space Sci. Rev. 
9, 243 (1969). 

A. J. Kliore, G. Fjeldbo, B. Seidel, in prepa- 

M J. Trask, Tech. Rep. Jet Propul. Lab. 
Calif. Inst. Technol. No. 32-800 (1966), 
p. 252. 

G. E. Fischbacher, L. J. Martin. W. A. 
Baum, "Martian Polar Cap Boundaries." final 
report under Jet Propulsion Laboratory con- 
tract 951547, Lowell Observatory, May 1969. 
E. Burgess, private communication. 
R. M. Goldstein, private communication; C. 
C. Councilman, private communication. 
M. J. S. Belton and D. M. Hunten. Science, 
in press. 
W. K. Hartmann, Icarus 5, 565 (1966). 

20. D. L. Anderson and R. A. Phinney, in Man- 
tles of the Earth and Terrestrial Planets, S. K. 
Runcorn, Ed. ( Interscience, New York, 
1967). pp. 113-126. 

21. E. Anders and f. R. Arnold, Science 149, 
1494 (1965). 

22. R. B. Leighton and B. C. Murray, ibid. 153, 
136 (1966). 

23. B. T. O'Leary and D. G. Rea, ibid. 155, 
317 (1967). 

24. A. E. J. Engel, B. Nagy, L. A. Nagy, C. G. 
Engel, G. O. W. Kremp, C. M. Drew, ibid. 
161, 1005 (1968); J. W. Schopf and E. S. 
Barghoorn, ibid. 156, 508 (1967). 

25. R. J. Trumpler, Lick Obs. Bull. 13, 19 

26. We gratefully acknowledge the support and 
encouragement of the National Aeronautics 
and Space Administration. An undertaking as 
complex as that of Mariners 6 and 7 rests 
upon a broad base of facilities, technical staff, 
experience, and management, and requires not 
only money but much individual and team 
effort to be brought to a successful conclu- 
sion. It is impossible to know, much less to 
acknowledge, the important roles played by 
hundreds of individuals. We are deeply ap- 
preciative of the support and efforts of H. M. 
Schurmeier and the entire Mariner 1969 proj- 
ect staff* With respect to the television sys- 
tem, responsibility for the design, assembly, 
testing, calibration, flight operation, and pic- 
ture data processing lay with the Jet Propul- 
sion Laboratory. We gratefully acknowledge 
the contributions of G. M. Smith, D. G. 
Montgomery, M. C. Clary, L. A. Adams, 
F. P. Landauer, C. C. LaBaw, T. C. Rind- 
fleisch, and J. A. Dunne in these areas. L. 
Mailing, J. D. Allen, and R. K. Sloan made 
important early contributions. We are in- 
debted to V. C. Clarke, C. E. Kohlhase, R. 
Miles, and E. Greenberg for their help in 
exploiting the flexibility of the spacecraft to 
achieve maximum return of pictorial data. 
We are especially appreciative of the broad 
and creative efforts of G. E. Danielson as 
Experiment Representative. The able collab- 
orative contributions of J. C. Robinson in 
comparing Mariner pictures with Earth-based 
photographs and of L. A. Soderblom and 
J. A. Cutts in measuring craters are grate- 
fully acknowledged. 


A dramatized account of the boyhood of the Japanese 
astronomer who discovered a recent comet. This same 
comet, Ikeya-Seki, is described also in the following 

The Boy Who Redeemed His Father's Name 

Terry Morris 

An article from Redbook, 1965. 

With a homemade telescope that cost only $22.32, 
Kaoru Ikeya searched the skies for 109 nights, until he 
made a discovery that brought honor to his family 

As she had done many times, Mrs. Ikeya woke when 
her son Kaoru did and, unnoticed by him, saw him 
preparing for sky-watching. All the other children, 
stretched out beside her on the tatami matting, slept 
soundly under their quilts. Only her eldest son] 
mainstay of this fatherless house, refused to take his 
full rest before going to work the next morning. 
Winter nights are cold in Japan. Moving quieUy, Kaoru 
drew on his leather windbreaker, heavy work pants, 
wool scarf and gloves. Carrying his bed quilt with him, 
he left the house to climb an outside ladder to his 
rooftop perch beside his telescope. 

Mrs. Ikeya closed her eyes and tried to go back to 
sleep, but couldn't. Instead, she lay listening to the 
bitter wind as it swept in from the Pacific and blew 
across Lake Hamana, just outside the door. 

No matter how bizarre his behavior might seem 
to others, Mrs. Ikeya felt that she owed her son 
understanding and acceptance. Yet when she saw 
him, pale, too thin, and haggard from lack of sleep, 
she often had to stifle a protest. 

By this night of January 2, 1963, 
19-year-old Kaoru Ikeya had logged a 
total of 335 hours and 30 minutes of 
observing the sky in a period of 109 
nights; and there had been countless 
nights before he began his official 
log. Yet each time he peered 
through the eyepiece of 
the telescope he had 


made with his own hands, his pulse quickened in 
expectation. Kaoru had set himself a goal. More than 
anything else, he wanted to be the discovered of 
a new comet. 

Kaoru adjusted the eyepiece and almost at once 
sighted in the sky a misty object he had never noticed 
before. He consulted his sky maps. They showed 
nothing in that location. Thoroughly roused, he 
rechecked its position meticulously, then remained 
glued to his telescope, half-convinced that what he was 
seeing must be a delusion. But the small, round, 
diffuse glow remained in the sky, and observing its 
gradual movement among the stars, Kaoru positively 
identified it not as a faint star cluster but a coma, 
the head of a comet. 

But was it his comet? Or was he witnessing the 
return of a comet already recorded? Only when the 
Tokyo Astronomical Observatory had checked out his 
data would he know whether he had made a discovery. 

Next morning Kaoru waited outside the telegraph 
office before it opened to dispatch a wire to the 
observatory reporting the comet's position three degre 
southwest of star Pi in the constellation Hydra, its 
12th-magnitude brightness and its direction of 
movement. Then, mounting his bicycle, he pedaled 
off to work. 

Before the whistle blew at 8 a.m., hundreds of 
workers from surrounding towns had parked their 
bicycles within the gates of the huge plant of the 
Kawai Gakki Company, manufacturers of 


The Boy Who Redeemed His Father's Name 

pianos. In visored cap and factory coveralls, 

Kaoru Ikeya, a slight figure standing 

five feet four inches and weighing 

a bit under 125 pounds, was at 

once absorbed into the 

anonymity of the assembly fine, 

where as an ungraded, or 

unskilled, worker he polished 

the white celluloid sheaths for 

piano keyboards at a salary of 

13,000 yen, or about $35, 

per month. 

But Kaoru's thoughts were 
not on factory work. He had 
refused special training to 
upgrade himself at the piano 
company, and once again he was 
grateful that his job demanded so little of him 
Polishing celluloid was mechanical; he could 
think of other things. 

"A steady fellow," his personnel card read. "Reliable 
Quiet. Middle school education only. Nonparticipant 
in company sports or hobby clubs. . . . Lacks ambition 
and initiative." 

Within a few days after Kaoru received his reply 
wire from the Tokyo Observatory, the international 
news services were flashing quite another profile: 

"Self-taught 19-year-old amateur astronomer 
Kaoru Ikeya, using a reflector telescope he constructed 
by himself at a cost of $22.32, has discovered the 
New Year's first comet, officially designated Comet 
Ikeya 1963a and now the subject of observation 
and tracking by astronomers in both hemispheres." 

A spate of publicity greeted Kaoru's discovery. His 

home was in- 
vaded by news 

he was led before TV cameras and radio hookups; 
he received more than 700 letters from amateur 
astronomers seeking his advice; he "was awarded a gold 
medal by the Tokyo Observatory; and he watched 
in polite silence a professional actor portray him in a 
hackneyed, melodramatic version of his life story, 
an "inspirational" 40-minute movie short called 
Watching the Stars, which was to be shown to the 
school children of Japan. 

Aglow with pride at the honors heaped on her son, 
Mrs. Ikeya saw the film through rose-colored glasses. 

But Kaoru did not share her bias. "This movie is a 


novel, a fiction about me," he commented wryly. "Why 
isn't the truth good enough?" 

The truth was neither hackneyed nor melodramatic. 
To begin with, if his father had not moved the family 
from the large industrial city of Nagoya to the town of 
Bentenjima when Kaoru was six years old, Kaoru would 
probably have acquired a city boy's indifference to the 
sky, observing it only in bits and patches between 
buildings. But their house fronted on Lake Hamana, a 
salt-water lake fed by the Pacific, and the flat roof 
offered a perfect platform for observing a far-flung 
canopy of the heavens. As the family grew and Kaoru 
sought to escape from the noisy clamor of three- 
younger brothers and a sister, he often mounted to 
the quiet rooftop to look at the stars. 

In addition, there were Japanese holidays that had 
stimulated his interest in the stars. For as long as he 
could remember, he had joined with other boys and 
girls in hanging strips of colored papers bearing poems 
and pictures on stalks of bamboo that had been set up 
outdoors. These were directed to the two celestial lov- 
ers, the Weaver Star and the Cowherd Star, who, so 
the story goes, live on either side of the Milky Way 
and meet only once a year, on the night of the festival. 
In the middle of or in late September of each year 
there was also Tsukimi, a special holiday when all 
Japan makes offerings of trays of rice dumplings and 
clusters of seven autumn flowers to the new full moon. 

Oy the time he was 11 years old Kaoru was highly 
"sky conscious." He was so enthralled with the mystery 
of the heavens that he had begun to look for books in 
his school library that would tell him more about the 
stars, and to trace maps and diagrams of the skies into 
his school notebook. Tentatively at first, then widi 
deepening familiarity, he began to distinguish among 
the galaxies and constellations and to wish to see more 
than he could with his naked eye. What fascinated 
him most were comets, those ghostly celestial bodies 
so nebulous as to be commonly described in his books 
as "the nearest thing to nothing that anything can be 
and still be something." Kaoru made up his mind. It 
was a new comet that he longed to discover-a comet 
ol his own, with its fuzzy head surrounding a bright 
nucleus, its long, ephemeral tail pointing away from 
the sun and its journey through the skies lasting from 
three to thousands of years. 

There was still another holiday that made an im 
pression on Kaoru during his early years. Every May 
5th, on the national holiday known as Boys' Day, the 
Ikeya family, along with others among their neighbors 
who were fortunate enough to have sons, held a special 

celebration. On tall poles next to their houses they dis- 
played el,, (I, streamers In five colors made in the image 
of Japan's favorite fish, the river carp. Proudly the 
Ueeva pole flew six earp. oik- for each son of the house 

and one foi each parent. Poor Fumiko, the sole daugh 

ter of the house, was given new dolls to placate her. 

Then Mr. Ikeya lined up his sons and exhorted them 
to grow up to be good citizens. In emulation of the 
carp's brave, vigorous struggle upstream, he said, they 
must aspire ever higher in their own lives. 

By the time Kaoru was 12 and had had the six years 
of elementary school, he had determined to build his 
own telescope. Although his father's fish market was 
prospering, Kaoru was reluctant to ask him to buy one. 
Already diere was tension between them. Instead of 
applying himself to learning the family's business, his 
father complained, Kaoru's head was "always in the 

Mr. Ikeya was still moored to the old, prewar atti- 
tudes. "Sound sense should show you, my son," he 
insisted, "that astronomy does not belong to our station 
in life." 

How, Kaoru wondered silently, did his father's an- 
nual Boys' Day message square with this contention? 
How much higher could one aspire than to the stars? 
In contrast to his father, Kaoru was growing up in a 
postwar Japan heavily influenced by the Americans 
who occupied the country. In response to reforms en- 
acted in the New Education Law of 1947, his teachers 
from first grade on rejected the old emphasis on passive, 
rote learning and memorizing. Instead, they encour- 
aged questions and discussions and created projects 
that his father called a foolish waste of time. 

Ihe new way also widened Kaoru's horizons outside 
the classroom. In the spring and fall he was among die 
hundreds of thousands of school children who took 
off on excursions to parks, monuments, temples and 
shrines. The Get-To-Know-Japan program, under 
which the participants were chaperoned by teachers 
and billeted at hostels and inexpensive inns, was so 
inexpensive that by contributing pennies into the class 
travel fund each week, Kaoru could afford to take 
advantage of it. 

In middle school, where he completed the nine years 
of compulsory education, Kaoru was a good student, 
ranking fifth in a class of 50 students. But he had no 
favorite subjects. "Except, of course, the one I thought 
about and worked at by myself," he says. 

Astronomy was not taught in middle school, but 
Kaoru haunted the school library, reading texts on 
astronomy and studying the principles of optics, physics 
and chemistry involved in telescope-making. With his 
meager savings he also managed to buy a number of 
do-it-yourself manuals on how to build a telescope. He 
was barely 14 when, reading an astronomy journal, he 
came ac toss the name of Dr. Hideo Honda, an ophthal- 
mologist in Nagoya who held monthly meetings for 
amateur astronomers in his clinic. 

Kaoru wrote to Dr. Honda that he was planning to 
construct a Newtonian reflector telescope with a 20-cm. 
or 8-inch mirror-die most popular and feasible for do- 
it-yourself amateurs. Noting that his young correspond- 
ent was only 14, Dr. Honda didn't think the bov would 


The Boy Who Redeemed His Father's Name 

have either the skill or the stamina to see his project 
through. On the other hand, he was reluctant to dis- 
courage Kaoru. 

"I think," he replied cautiously, "that you are very 
likely too young to make a 20-cm. mirror. Your idea 
presents many difficulties and I shall tell you all I know 
about them. But so many young men in Japan after the 
war are impatient, especially with regard to making 
observations. Although many have high-priced tele- 
scopes, they rarely observe the stars. They use their 
fine instruments only to watch an eclipse of the sun or 
some other show in the heavens. Few of them would 
be able to take the pains to construct their own in- 

Kaoru reflected that Dr. Honda could not possibly 
understand how prepared he really was— at least to 
take infinite pains. He continued with his studies and 
gradually began to acquire the materials needed for 
making his telescope. It was at about this time that 
misfortune struck the Ikeya family. 

For some time Mr. ikeya's fish market had been 
failing. The reasons he ascribed to this were "price- 
fixing by ignorant and officious Japanese and American 
policy makers," but also, he pointed out, it was retribu- 
tion by the gods, who were angered by the way Shinto 
beliefs were being shunted aside. 

Discouraged and embittered, Mr. Ikeya began to 
lounge about the cafes, drinking sake, increasingly re- 
luctant to face his family or five young children. Early 
in 1958 he resolved his dilemma by disappearing, 
abandoning them all. 

Perhaps nowhere else in the world does a father's 
desertion so cruelly punish those he leaves behind as 
in Japan, where the concept of on heavily influences 
individual behavior. On refers to the obligations each 
person incurs through contact with others by the mere 
fact of his existence. The most basic form of on is ko, 
the obligation to one's parents for the daily care and 
trouble to which they are put; even by offering un- 
wavering loyalty, obedience and reverence, no more 
than one ten-thousandth of this debt can ever be paid. 
This particular duty, ko, also imparts the same obliga- 
tions to descendants. A Japanese proverb says: "Only 
after a person is himself a parent does he know how 
indebted he is to his own parents." It follows, then, 
that a significant part of ko is to one's own parents in 
giving as good or better care to one's children. 

In deserting his family, Mr. Ikeya not only failed 
utterly in his duty as a parent but violated his most 
sacred on of filial duty to his own parents. He placed 
an oppressive burden of shame on them all and tar- 
nished the family name, perhaps for generations. 

"We could think of nothing else, my mother and I," 
Kaoru says, "but that our family was disgraced, our 
house destroyed." 

The first and hardest impact of the disaster was on 
Mrs. Ikeya. Sadly Kaoru watched his mother go to work 
at the hotel near the Bentenjima railroad station, cook- 
ing and cleaning for strangers instead of in the seclu- 

sion of her own house and family. But, as she observed 
to him, at least the older children were safe in school 
during the day and she could keep the baby, four-year- 
old Yasutoshi, with her on the job. Although she was 
under five feet tall and even in her bulky, padded house 
jacket, trousers and coverall apron looked slight as a 
sparrow, her strength and fortitude in dealing with this 
family crisis were immense. What she told herself was 
that the money she earned, around 17,000 yen a 
month, or about $47, ensured food for her children. 

Kaoru felt the weight of his love and duty toward 
his mother. But until he completed the compulsory 
third year of middle school he could do no more to 
lighten her burden than to take a part-time job, rising 
at five a.m. to deliver morning newspapers before 
school, then returning after classes to deliver the eve- 
ning edition. Of course, attendance at high school was 
barred to him. The family could not afford either the 
time or the fees, which amounted to about $25 for 
registration and about $8 per month. 

Mrs. Ikeya's and Kaoru's combined efforts were in- 
adequate to keep up payments on their comfortable, 
roomy house. The bank foreclosed and permitted them 
to move, virtually rent-free, into a far less adequate 
house a few doors away. 

This house provided a narrow entry-way, an all- 
purpose eating-sleeping-living room, a tiny kitchen, a 
catchall cubicle and a lavatory at the back. But in 
common with most Japanese houses it was orderly and 
simple to keep clean, since shoes, which might track 
up the tatami on which families bed down at night, are 
never worn inside Japanese houses. In the Ikeya home 
the furniture consisted of a bureau, a square low tabic 
with floor cushions, Kaoru's worktable, and two rough 
shelves that he constructed to hold his small collection 
of books and manuals. No Japanese houses have cen- 
tral heating, and the Ikeyas relied on a large porcelain 
jar filled with heated charcoal briquets. Even well-to- 
do families have nothing more than a hibachi, a pit in 
the floor filled with charcoal. 

The feature of the house that most concerned Kaoru 
was the flat roof, which provided as good a platform 
and as good a sky to view as before. On his shoulders 
rested the responsibility not only of replacing his father 
as breadwinner and head of the house, but of some- 
how removing from the family name the stigma his 
father had attached to it. More than ever he thought 
about his comet. What if one day he could attach the 
dishonored name to the tail of a new comet and write 
that name across the sky? New comets were generally 
named after their discoverers. "Comet Ikeya!" The 
name had a fine, proud ring to it! 

In June, 1959, when he graduated from middle school, 
Kaoru was deeply immersed in his thoughts about tele- 
scope building, but he paused long enough to get a 
job at the Kawai Gakki piano Factory, a few miles from 
home. Since degree of education is directly and, on the 


whole, inflexibly related to earning power in the Japa- 
nese economic scale, Kaoru was classified as an un- 
graded or unskilled worker at base pay. 

Kaoru wasn't disturbed. "It's a simple job," he re- 
ported to his mother. "It will not bother me." 

Mrs. Ikeya also was content. Although the Japanese 
are now more concerned with money-making and 
worldly success than before World War II, with its 
postwar Western influences, many still place greater 
emphasis on the reflective life and spiritual values. On 
the practical side of her ledger, Kaoru's base pay and 
regular annual raises, together with her own earnings, 
were enough for the necessities of life. Soon, too, Ta- 
dashi, her second son, only two years younger than 
Kaoru, would also become a wage earner. She didn't 
attempt, though, to budget the spiritual side of the 
ledger. She would be a poor mother indeed if she 
offered Kaoru anything but encouragement and the 
greatest freedom, within the confines imposed on him 
by necessity, to follow his own pursuits. Who knew? 
Perhaps he would even attain Buddhahood through 
the ordeals he imposed on himself. 

Kaoru set to work grinding the high-precision sur- 
face for the main mirror that would go into his tele- 
scope. Shopping around in secondhand supply stores, 
he obtained the last-minute materials he needed. Bit 
by bit, and after trial and error, Kaoru, still thinking 
for himself and going it alone, completed the prelim- 
inary work, and then began the final process of assem- 
bling and mounting his telescope on the roof. In August, 
1961, he was ready to begin once more to search the 
skies. Since starting work at the factory he had put 
nearly two years of off-work hours of labor into achiev- 
ing his telescope, at a total out-of-pocket cost of 8,000 
yen, or about $22. 

In Japan, the best hours for viewing are from 3 a.m. 
to 5 a.m., but of course, not every sky is fit for obser- 
vation. On cloudy mornings Kaoru caught up on the 
sleep he lost during clear mornings, when the predawn 
spectacles thrilled him. He logged his watches meticu- 
lously and checked back with his sky maps, but six 
months after he had begun to search regularly, Kaoru 
felt deeply discouraged. The search for a new comet 
seemed futile. More and more often he began to fall 
into a mood of profound depression. 

"My son," Mrs. Ikeya said, "you are too much alone 
with your thoughts. Is there no one you could talk to 
who would give you advice?" 

Perhaps she was right. Kaoru broke out of his soli- 
tude to establish communication with someone who 
had known not only the trials of comet-seeking but also 
the rewards. He wrote to the astronomer Minora Hon- 
da, discoverer of nine comets, about his lack of suc- 
cess, pleading between the lines for a word of en- 

At first the reply seemed to him almost a rebuff. Then, 
pondering it, Kaoru seized eagerly on its meaning. 

"To observe the skies solely to seek a new comet is 
a hopeless task which demands a great deal of time 
and hard labor," Minora Honda wrote. "But to observe 
the brilliant heavens for their own sake without thought 
of a discovery may bring good luck to your comet- 
seeking. You must have humility and not be too ambi- 
tious, for, after all, you are quite young and only an 

Kaoru returned to his sky watches. He tried to main- 
tain a humbler and more relaxed attitude. He still had 
a great deal to learn about the heavens, and instead of 
searching for a comet in particular, he concentrated on 
the whole sky, trying to become as familiar with its plan 
as he was with the streets and byways of Bentenjima. 

On December 31, 1962, Mrs. Ikeya counted a total 
of 16 months since Kaoru had begun his night vigils 
with his new telescope. 

"Surely, Kaoru," she pleaded, "this first night of the 
holidays you will take your full rest. It is Omisoka, 
after all, the Grand Last Day of the year! Both of us 
have worked hard. We have honorably settled all our 
debts, and can start the new year with a clean record. 
Let us stay awake until midnight, listening to the tem- 
ple bells, and then sleep late in the morning." 

To please her, Kaoru didn't climb to the roof that 
night, and all through New Year's Day he remained 
with the family, enjoying his mother's holiday meal of 
ozoni (rice cake soup), playing her favorite game of 
cards, karuta, and then joining her for a visit to a 
nearby shrine to pray for good luck in 1963. 

It was on the following night of January 2, 1963, 
while he was still in a relaxed, holiday mood, that 
Kaoru made his 109th search and discovered his comet. 

At the Harvard Observatory, the western hemi- 
sphere's clearinghouse for astronomic information, all 
the data on Comet Ikeya 1963a, together with a pro- 
jection of its orbit, were placed on announcement 
cards and sent to observatories, journals of astronomy 
and a network of professional and amateur astrono- 
mers around the world. 

The comet changed its form and brightness nighdy 
as it reached its maximum visibility at perihelion, or 
closest passage to the sun, calculated to take place on 
March 21st. At this point Comet Ikeya would be 59 
million miles distant from the sun and some 93 million 
miles from the earth. Then the celestial spectacle it 
offered would be over until late spring, when it would 
become visible again in the morning sky, a consider- 
ably fainter object on the far side of the sun. Finally, 
traveling in an elliptical orbit out beyond the farthest 
planets, it would disappear, to return anywhere from 
100 to 10,000 years hence. 

Comet Ikeya 1963a was at first described as dim, 
but a few weeks after Kaoru sighted it, reports from 
Tokyo, the Yerkes Observatory, in Wisconsin, and the 
U.S. Naval Observatory's station at Flagstaff, Arizona, 
indicated that it was moving rapidly southward and 

By February and early March, 1963, Comet Ikeya 


The Boy Who Redeemed His Father's Name 

was providing an exciting spectacle for southern hemi- 
sphere watchers. In four weeks, beginning February 
13th, it had traveled northward a quarter of the way 
around the sky and become an object visible to the 
naked eye. 

An American physicist then working in Sydney, Au- 
stralia, wrote to the journal Sky and Telescope of his 
experience with the comet: 

"On February 14th I had my children in the back 
yard to show them 47 Tucani, a very beautiful globu- 
lar cluster. My daughter Judy was looking through 
binoculars and remarked that what she saw was be- 
tween the Magellanic Clouds. When I looked, I real- 
ized that she had not been viewing 47 at all, but a 
new comet— actually Ikeya's." 

Kaoru kept in touch with his comet through a widen- 
ing circle of fellow observers, but his most immediate 
source was the Tokyo Observatory and its staff mem- 
bers, notably Dr. Masahisa Tarao, distinguished astron- 
omer and vice-president of the Japanese Astronomical 
Society, on whose behalf he presented Kaoru with the 
gold medal for achievement. 

"We professional astronomers cannot watch the 
heavens all the time," Dr. Tarao said. "We need the 
assistance of amateurs in the observation of artificial 
satellites, solar explosions, meteors, comets and other 
phenomena of our universe. You, Kaoru Ikeya, by your 
patience and diligence, have added to our knowledge 
of the solar system." 

A H this while, Kaoru reported for his job at the piano 
factory, quietly and reliably. Only when the press re- 
quested interviews with Kaoru did the company learn 
of his achievement. The company's response was to 
initiate a collection among the workers to help Ikeya 
continue his work. A certificate lauding Kaoru's off- 

the-job zeal and dedication together with a check for 
about $300, a lordly sum in Japan, were presented to 
him at a ceremony at the plant. The company also 
financed the movie short about Kaoru's life, and paid 
him 30,000 yen, or about $80, for permission to make 
the film. 

Kaoru made no effort to capitalize on his publicity. 
To have achieved a magnificent "first" in comet-hunt- 
ing was all the reward he needed, and his appreciation 
of it deepened when he learned of other amateur 
astronomers such as Dr. Floyd L. Waters, of Hugo, 
Oklahoma, who very nearly made it, but did not quite. 

"On the morning of January 26th," Dr. Waters wrote 
Kaoru, "at about 5 a.m., temperature 10 above zero, I 
discovered this object in the south. 1 became quite 
excited, wired my finding to Harvard Observatory, and 
found out later that day that what I had reported was 
the Comet Ikeya that had been discovered by a boy 
in Japan on January 2nd. All amateur astronomers 
would be very thrilled to discover a comet but of 
course do not have the perseverance to spend 335 hours 
trying to find one!" 

But Comet Ikeya was not the last of Kaoru's discov- 
eries. As if especially favored by the gods, Kaoru made 
a second discovery in June, 1964. Working with a 
new, improved telescope with a 17.5-cm. mirror, which 
he had made at a cost of 5,000 yen, or about $13, he 
discovered a second comet— Comet 1964f. 

Still in the same job at the factory, Kaoru has neither 
sought after nor been offered the reward of advance- 
ment. For him the greatest advancement, according to 
his Buddhist faith, would be to find that "limitless, 
ever-expanding path, an eternal path to tranquility." 
For the rest, his richest reward has been that in the 
span of his 21 years he has made partial payment on 
his ko, or primary duty to his mother and to his family, 
by taking a dishonored name and writing it across the 


The director of the Central Bureau for Astronomical 
Telegrams describes the excitement generated by a 
recent comet, and reviews current knowledge of 

16 The Great Comet of 1965 

Owen Gingerich 

An article from The Atlantic Monthly, 1966. 


"f all the memorable comets that have excited 
astronomers and stirred men's imaginations, not 
one had more impact on our concepts of the uni- 
verse than the Great Comet of 1577. Discovered in 
November of that year, the comet stood like a 
bent red flame in the western sky just after sunset. 
The celebrated Danish astronomer Tycho Brahe 
was among the early observers: he caught sight of 
the brilliant nucleus while he was fishing, even 
before the sun had set. As darkness fell, a splendid 
twenty-two-degree tail revealed itself. Tycho's 
precise observations over the ten-week span before 
the comet faded away were to deal the deathblow 
to ancient cosmogonies and pave the way for 
modern astronomy. 

In the sixteenth century nearly everyone ac- 
cepted Aristotle's idea that comets were meteoro- 
logical phenomena, fiery condensations in the 
upper atmosphere. Or, if not that, they were burn- 
ing impurities on the lower fringe of the celestial 
ether, far below the orbit of the moon. In 1577 
most astronomers still subscribed to the ancient 
belief that the moon and planets were carried 
around the earth on concentric shells of purest 
ether. Tycho, by comparing his careful measure- 
ments of the comet's position with data from dis- 
tant observers, proved that it sped through space 
far beyond the moon. The Comet of 1577 com- 
pletely shattered the immutable crystalline spheres, 
thereby contributing to the breakdown of Aris- 
totelian physics and the acceptance of the Coper- 
nican system. 

But the most renowned and most thoroughly 
studied of all comets is the one associated with 
Edmund Halley. It was the first to have a periodic 
orbit assigned, thus securing for comets their place 
as members of the solar system. Halley had matched 
the Comet of 1682, which he had observed, with 
those of 1531 and 1607. Assuming these to be 
different appearances of the same celestial object, 
he predicted another return in 1758. Although he 


The Great Comet of 1965 

was ridiculed for setting the date beyond his 
expected lifetime, the comet indeed returned, and 
Halley's name has been linked with it ever since. 
On its latest return, in 1910, Halley's comet put 
on a magnificent display, reaching its climax 
several weeks after perihelion passage in mid-April. 
During the early part of May it increased until 
the brilliance of its head equaled the brightest stars 
and its tail extended sixty degrees across the sky. 
Later in May, the earth grazed the edge of the tail. 
The thin vacuous tail caused no observable effect 
on earth, except for such human aberrations as 
the spirited sale of asbestos suits. That no terres- 
trial consequences were detected is not surprising 
when we learn that 2000 cubic miles of the tail 
contained less material than a single cubic inch of 
ordinary air. 

.Lf prizes were offered for cometary distinctions, 
then last year's Comet Ikeya-Seki would win a 
medal as the most photographed of all time, and it 
might win again for the range of astrophysical 
observations carried out. As it swung around the 
sun, its brilliancy outshone that of the full moon, 
and within ten days its tail extended almost as far 
as the distance from the earth to the sun. The 
behavior of the comet was neatly explained by the 
"dirty snowball" theory. According to this widely 
accepted picture, a comet's nucleus is a huge block 
of frozen gases generously sprinkled with dark 
earthy materials. Occasionally the gravitational 
attraction of nearby passing stars can perturb a 
comet from its cosmic deep freeze in the distant 
fringes of the planetary system beyond Neptune; 
the comet then can penetrate the inner circles of 
the solar system, where it develops a shining 
gaseous shroud as its surface vaporizes under the 
sun's warming rays. Hence, the closer a comet 
approaches the sun, the more it vaporizes and the 
larger and brighter it becomes. Comet Ikeya-Seki 
passed unusually close to the sun, becoming pos- 
sibly the brightest comet of the century; the 
resulting tail was the fourth longest ever recorded. 

Today I look back with a wry smile to the Sunday 
morning last September when I decoded the tele- 
gram bringing the first word of the new comet. 
Early that morning in Benten Jima, Japan, a 
youthful comet hunter, Kaoru Ikeya, had dis- 
covered a fuzzy glow not charted on his sky maps. 
At the same time, another young amateur 250 
miles away, Tsutomu Seki, had independently de- 
tected the new celestial visitor. Both men had 
used simple, homemade telescopes for their dis- 
covery, and both had sent urgent messages of their 
find to the Tokyo Astronomical Observatory. 

News of the comet's appearance was quickly 

relayed from Tokyo to my office at the Smithsonian 
Astrophysical Observatory. Here the name "Comet 
Ikeya-Seki" was officially assigned, as well as the 
astronomical designation 1965 f. Throughout that 
day, September 19, the communications center at 
Smithsonian alerted observatories and astronom- 
ical groups all over the world — Flagstaff, Rio de 
Janeiro, Johannesburg, Prague, Peking, Canberra 
— in all, more than 120. Included were the twelve 
astrophysical observing stations of the Smithsonian 
Observatory, whose specially designed satellite- 
tracking cameras are ideal for comet photography. 
Within hours a confirmation of Ikeya-Seki arrived 
from the Woomera, Australia, station. 

By Tuesday afternoon, half a dozen approximate 
positions were in hand, more than enough for us 
to try for a crude preliminary solution of the comet's 
orbit. Unfortunately, the positions from the ob- 
serving stations were only approximate "eyeball" 
measurements obtained by laying the film onto a 
standard star chart with marked coordinates. 
Furthermore, the observatory's computer program 
had not been fully checked out. When the rough 
observations were used in different combinations, 
the computer produced two orbits in wild disagree- 
ment. Nevertheless, Professor Fred L. Whipple, 
director of the Smithsonian Astrophysical Observa- 
tory and author of the "dirty snowball" comet 
theory, noted that the second of the preliminary 
orbits closely resembled the path of a famous 
family of sun-grazing comets. The agreement was 
too close to be coincidence, he reasoned, and there- 
fore the second solution must be correct. 

Professor Whipple's astute suggestion provided 
the first hint of the excitement that was to come. 
Several of the previous sun-grazers had been 
spectacular objects. Notable among them was the 
Great Comet of 1843, whose seventy-degree tail 
stretched 200 million miles into space, setting an 
all-time record, and whose brilliance induced the 
citizenry of Cambridge to build a fifteen-inch 
telescope for Harvard equal to the largest in the 
world. And the second comet of 1882 achieved 
such brilliancy as it rounded the sun that it could 
be seen in broad daylight with the naked eye. 

In the few days following the first computer 
solutions three "precise" positions were reported to 
the Central Telegram Bureau, one from Steward 
Observatory in Tucson, Arizona, and two from 
the Skalnate Pleso Observatory in Czechoslovakia. 
When these new positions were fed by themselves 
into the computer, the result indicated an ordinary 
comet, and not a sun-grazer at all. But our pro- 
grammers noticed that something was seriously 
wrong. When positions from the satellite-tracking 
cameras were included in the calculations, the 
computer gave different answers. Among them 
was the interesting possibility that Comet Ikeya- 


Seki might die by fire, plunging directly into the 

Then, suddenly, the mystery vanished. Six 
accurate positions from veteran comet observer 
Elizabeth Roemer at the Flagstaff, Arizona, station 
of the U.S. Naval Observatory established the path 
with great precision. One of the earlier "precise" 
observations had been faulty, and with its elimina- 
tion, the others fell into place. Comet Ikeya-Seki 
was accelerating along a course that would carry 
it within a solar radius of the sun's surface. And 
since a comet's brightness depends on its closeness 
to the sun, there was every indication that Comet 
Ikeya-Seki would become a brilliant object. 

Armed with predictions of Comet Ikeya-Seki's 
sun-grazing path, the Smithsonian staff set out to 
forewarn space scientists and radio astronomers 
whose attention does not normally encompass 
comets. We called a press conference to describe 
the magnificent view hoped for as the comet swung 
around perihelion, its nearest approach to the sun. 
First discovered in the morning sky, the comet 
would cross into the evening sky for only a few 
hours on October 21 . If a tail of this comet were to 
appear in the evening, it would sweep across the 
western sky after sunset on that evening. After- 
ward it would reappear in the morning twilight. 
Such a prediction was hazardous, because although 
the comet's trajectory was well established, its 
brightness and tail length resisted astronomical 
forecasting since no one knew just how much mate- 
rial would be activated as it sped past the sun. 

Had we examined more carefully the historical 
records of Comet 1882 II, we might have been 
more cautious in telling the public to look for the 
tail of Comet Ikeya-Seki sweeping across the 
western sky after sunset on October 21. Each new 
observation of the 1965 comet confirmed that it 
was a virtual twin of the Great Comet of 1 882 ; thus, 
by looking at the observations from the last century, 
we should have guessed that the comet's enormous 
velocity as it rounded the sun — one million miles 
per hour — would dissipate the tail so widely that 
it could not be seen in the dark sky. On the other 
hand, we hardly dared publicize what the com- 
puter's brightness predictions showed: that Comet 
Ikeya-Seki would be visible in full daylight within 
a few degrees of the sun ! 


lNd thus it happened that thousands of would-be 
observers in the eastern United States maintained a 
cold and fruitless search in the early morning hours 
of October 21. Thousands of others, especially in 
the American Southwest, had the view of a lifetime 
— a bright comet with its short silvery tail visible 
next to the sun in broad daylight. Simply by 

holding up their hands to block out the sunlight, 
they could glimpse the comet shining with the 
brilliance of the full moon. Hazy, milky skies 
blocked the naked-eye view for observers in the 
eastern United States and much of the rest of the 
world; even in New England, however, telescopes 
revealed the comet with a sharp edge facing the 
sun and the beginnings of a fuzzy tail on the other 
side. Professional astronomers were excited by the 
opportunity to photograph the object at high noon. 
For the first time, the daylight brilliance of a 
comet permitted analysis from solar coronagraphs. 
Airborne and rocket-borne ultraviolet detectors 
examined features never before studied in comets. 

The spectrum observations ended eight decades 
of controversy. In most comets, the reflected 
spectrum of sunlight is seen, combined with the 
more interesting bright molecular spectrum from 
carbon and carbon compounds. The molecules 
are excited by the ultraviolet light from the sun, 
and glow in much the same way that certain 
minerals fluoresce under an ultraviolet lamp. But 
back in 1882, when spectroscopy was in its infancy, 
the great sun-grazing comet yielded an entirely 
different spectrum. Scientists at the Dunecht 
Observatory in Scotland thought they saw emission 
lines from metal atoms such as iron, titanium, or 
calcium, but a similar spectrum was never found 
in subsequent comets. Some observers expressed 
their disbelief in this unique record. 

Astronomers did not get another chance to 
examine a comet so close to the sun until October 
20, 1965. On that morning at the Radcliffe 
Observatory in South Africa, Dr. A. D. Thackeray 
obtained spectrograms of the nucleus of Comet 
Ikeya-Seki, then only 8 million miles from the sun. 
These showed bright lines of both iron and calcium. 
The telegraphic announcement, again relayed by 
the Central Bureau, set other spectroscopists into 
action. Within days, there were reports of nickel, 
chromium, sodium, and copper. 

Though fully expected from a theoretical point 
of view, these observations confirmed that the 
impurities in comets had a chemical composition 
similar to that of meteors. The connection is not 
fortuitous; for many years astronomers recognized 
that those ephemeral streaks of light in the night 
sky, the meteors, were fragile comctary debris 
plunging through the earth's atmosphere. As the 
gases boil out of a cometary nucleus, myriads of 
dirty, dusty fragments are lost in space. In time, 
they can be distributed throughout a comet's 
entire orbit, and if that path comes close to the 
earth's own trajectory, a meteor shower results. 

The Leonid meteors are a splendid example 
of "falling stars" closely related to a comet. A 
meteor swarm follows close to Comet Tempel- 
Tuttle. Every thirty-three years, as the comet 


The Great Comet of 1965 

nears the earth's orbit, a particularly good display 
of Leonids appears around November 16. The 
recovery of this same comet in 1965 was followed 
by a November shower in which hundreds of 
brilliant meteors flashed through the sky within 
a period of a few hours. Nonetheless, the 1965 
Leonids provided a sparse show compared with 
the hundreds of thousands seen in 1833 and 1866. 
In 1899, astronomers predicted yet another fire- 
works spectacular. The prognostication proved to 
be a great fiasco, for gravitational attraction from 
the planet Jupiter had slightly shifted the orbit of 
the comet and its associated meteor swarm. Ever 
since, astronomers have been wary of alerting 
the public to meteors or comets. Our enthusiasm 
in predicting the greatness of Comet Ikeya-Seki on 
October 21 was indeed risky. 

Nevertheless, the daylight apparition of Comet 
Ikeya-Seki was but a prelude to a more spectacular 
show. Its surface thoroughly heated by its passage 
through the solar corona, the comet developed a 
surrounding coma of gas and dust some thousands 
of miles in diameter as it left the sun. As it slowed 
its course and receded from the hearth of our 
planetary system, the solar wind drove particles 
from that coma into a long stream preceding the 

As soon as Comet Ikeya-Seki could once again 
be seen in the early morning sky, its long twisted 
tail caused a sensation. Standing like a wispy 
searchlight beam above the eastern horizon, the 
tail could be traced for at least twenty-five degrees. 
Its maximum length corresponded to 70 million 
miles, ranking it as the fourth longest ever re- 
corded. Only the great comets of 1843, 1680, and 
1811 had tails stretching farther through space. 
(Quite a few comets have spanned greater arcs of 
the sky because they were much closer to the earth. 
Their actual lengths in space could not compare 
with that of the Great Comet of 1965.) At its 
peak brightness, Comet Ikeya-Seki was about equal 
to the sun-grazers of 1843 and 1882. Even after it 
receded from the sun, its nucleus shone brilliantly 
through the morning twilight. By all accounts, 
Comet Ikeya-Seki compared favorably with the 
great comets of the past. Those portentous sights, 
compared to giant swords by many a bygone 
observer, had little competition from city lights, 
smog, and horizon-blocking apartment buildings. 

Comet Ikeya-Seki surprised most astronomers by 
developing a strikingly brilliant tail on its outward 
path from the sun, especially when compared with 
the poor show on its incoming trajectory. Had 
they looked in Book III of Newton's Principia, 
however, they would have seen another sun- 
grazing comet neatly diagrammed with a short, 
stubby tail before perihelion passage and the great 
flowing streamlike tail afterward. Newton spent 

many pages describing that Great Comet of 1680. 
Especially interesting to American readers is the 
generous sprinkling of observations reported from 
New England and "at the river Patuxent, near 
Hunting Creek, in Maryland, in the confines of 

In the new world not only astronomers were 
interested in the comet. From the Massachusetts 
pulpit of Increase Mather came the warning, 

As for the SIGN in Heaven now appearing, what 
Calamityes may be portended thereby? ... As 
Vespasian the Emperour, when There was a long hairy 
Comet seen, he did but deride at it, and make a Joke of 
it, saying, That it concerned the Parthians that wore 
long hair, and not him, who was bald: but within a 
Year, Vespasian himself (and not the Parthian) dyed. 
There is no doubt to be made of it, but that God by this 
Blazing-star is speaking to other Places, and not to New 
England onely. And it may be, He is declaring to 
the generation of hairy Scalps, who go on still in their 
Trespasses, that the day of Calamity is at hand. 

Superstitions concerning comets reached their 
highest development and received their sharpest 
attacks at this time. For centuries comets had 
been considered fearsome omens of bloody catas- 
trophe, and Increase Mather must have been 
among the great majority who considered the 
Comet of 1680 as a symbol fraught with dark 
meanings. The terrors of the superstitious were 
compounded when a report came that a hen had 
laid an egg marked with a comet. Pamphlets were 
circulated in France and Germany with wood 
blocks of the comet, the hen, and the egg. Even 
the French Academy of Sciences felt obliged to 

Last Monday night, about eight o'clock, a hen which 
had never before laid an egg, after having cackled in 
an extraordinarily loud manner, laid an egg of an un- 
common size. It was not marked with a comet as many 
have believed, but with several stars as our engraving 

In a further analysis of this comet, Newton's 
Principia reported that a remarkable comet had 
appeared four times at equal intervals of 575 years 
beginning with the month of September in the 
year Julius Caesar was killed. Newton and his 
colleague Halley believed that the Great Comet of 
1680 had been the same one as seen in 1106, 531, 
and in 44 b.c. This conclusion was in fact false, 
and the Great Comet of 1680 had a much longer 
period. Within a few years, however, Halley cor- 
rectly analyzed the periodicity of the famous comet 
that now bears his name. 

Is Comet Ikeya-Seki periodic like Halley's? If 
so, can it be identified with any of the previous 
sun-grazers? The resemblance of Comet Ikeya- 
Seki to Comet 1882 II has led many people to sup- 
pose that these objects were identical. The orbits 


of both of these comets take the form of greatly 
elongated ellipses, extending away from the sun 
in virtually identical directions. Nevertheless, even 
the earliest orbit calculations scuttled the pos- 
sibility that the comets were one and the same, 
since at least several hundred years must have 
passed since Comet Ikeya-Seki made a previous 
appearance in the inner realms of the solar system. 
On the other hand, it is unlikely that Comet 
Ikcya-Seki, Comet 1882 II, and a half dozen oth- 
ers would share the same celestial traffic pattern 
and remain unrelated. The only reasonable ex- 
planation is to suppose that some single giant 
comet must have fissioned into many parts hun- 
dreds of years ago. 

Indeed, the Great Comet of 1882 did just that. 
Before perihelion passage, it showed a single 
nucleus; a few weeks afterward, astronomers de- 
tected four parts, which gradually separated along 
the line of the orbit. The periods for the indi- 
vidual pieces are calculated as 671, 772, 875, and 
955 years. Consequently, this comet will return as 
four great comets, about a century apart. 

It was, therefore, not at all unexpected when the 
Central Bureau was able to relay the message on 
November 5 that Comet Ikeya-Seki had likewise 
broken into pieces. The first report suggested the 
possibility of three fragments, but later observers 
were able to pinpoint only two. One of these was 
almost starlike, the other fuzzy and diffuse. Though 
first observed two weeks after perihelion passage, 
the breakup was probably caused by unequal 
heating of the icy comet as it neared the sun. 

If the Great Comet of 1965 was itself merely a 
fragment, what a superb sight the original sun- 
grazer must have been. Appearances of comets with 
known orbits total 870, beginning with Halley's in 
240 B.C., but the earliest known sun-grazer of this 
family is the Comet of 1668. In medieval chronicles 
and Chinese annals, and on cuneiform tablets, 
hundreds of other comets have been recorded, but 
the observations are inadequate for orbit deter- 
minations. Undoubtedly, that original superspec- 
tacular sun-grazer was observed, but whether it 
was recorded and whether such records can be 
found and interpreted are at present unanswerable 

A similar search of historical records, which 
holds more promise of success, is now under way 
at the Smithsonian Astrophysical Observatory. The 
comet with the shortest known period, Encke, 
cycles around the sun every three and a third 
years. Inexorably, each close approach to the 
sun lurther erodes Comet Encke. The size of its 
snowball has never been directly observed, but a 
shrewd guess based on the known excrescence of 
gaseous material places it in the order of a few 
miles. By calculating ahead, Professor Whipple 


has predicted the final demise of Comet Encke in 
the last decade of this century. By calculating 
backward in time, he has concluded that it might 
once have been a brilliant object. Its three-and-a- 
third-year period would bring a close approach to 
the earth every third revolution, so that a spectacu- 
lar comet might appear in the records at ten-year 
intervals. In the centuries before Christ, the 
Chinese and Babylonian records show remarkable 
agreement, but the register is too sketchy, and so 
far, Comet Encke's appearances in antiquity have 
not been identified. 

In addition to Encke there are nearly 100 
comets whose periods are less than 200 years. Like 
Comet Encke, they face a slow death, giving up 
more of their substance on each perihelion passage. 
On an astronomical time scale, the solar system's 
corps of short-period comets would be rapidly 
depleted if a fresh supply were unavailable. On 
the other hand, there is apparently an unlimited 
abundance of long-period comets that spend most 
of their lifetime far beyond the planetary system. 
Astronomers now envision an extensive cloud of 
hundreds of thousands of comets encircling the sun 
at distances well beyond Pluto. Originally there 
may only have been a ring of cometary material 
lying in the same plane as the earth's orbit — the 
leftover flotsam from the solar system's primordial 
times. Perhaps the density of material was insuffi- 
cient to coalesce into planetary objects, or perhaps 
at those great distances from the sun the snowballs 
were too cold to stick together easily. 

Gravitational attractions from passing stars pre- 
sumably threw many of the comets out of their 
original orbits into the present cometary cloud. 
These gravitational perturbations still continue, 
and a few comets from the cloud reach the earth's 
orbit every year. Their appearances are entirely 
unexpected, and their discoveries are fair game 
for professional and amateur alike. But since most 
professional astronomers are busily engaged in 
more reliable pursuits, persistent amateurs manage 
to catch the majority of bright long-period comets. 
Devotees such as Ikeya and Seki have spent 
literally hundreds of hours sweeping the sky with 
their telescopes in the hope of catching a small 
nebulous wisp that might be a new comet. The 
great sun-grazer was the third cometary find for 
each man. Within a week of its discovery, a 
British schoolteacher, G. E. D. Alcock, also found 
a new comet — his fourth. Alcock started his 
comet-finding career in 1959 by uncovering two 
new comets within a few days. 

How does an amateur, or a professional, recog- 
nize a new comet when he finds one? Most new- 
found comets are as diffuse and formless as a 
squashed star, completely devoid of any tail. In 
this respect they resemble hundreds of faint nebulae 

The Great Comet of 1965 

that speckle the sky, with this difference: nebulae 
are fixed, but a comet will inevitably move. Con- 
sequently, a second observation made a few hours 
later will generally reveal a motion if the nebulous 
wisp is indeed a comet. However, most comet 
hunters compare the position of their suspected 
comet with a sky map that charts faint nebulae 
and clusters. Then the discovery is quickly re- 
ported to a nearby observatory or directly to the 
Central Bureau. 

Today the chief reward for a comet find lies in 
the tradition of attaching the discoverer's name 
to the object, but in times past there have been 
other compensations. Jean Louis Pons, who dis- 
covered thirty-seven comets during the first quarter 
of the nineteenth century, rose from observatory 
doorkeeper to observatory director largely as a 
result of his international reputation for comet 
finding. And the Tennessee astronomer E. E. 
Barnard paid for his Nashville house with cash 
awards offered by a wealthy patron of astronomy 
for comet discoveries in the 1880s. Barnard has 
recorded a remarkable incident relating to the 
great sun-grazing comet of 1882: 

My thoughts must have run strongly on comets during 
that time, for one night when thoroughly worn out I 
set my alarm clock and lay down for a short sleep. 
Possibly it was the noise of the clock that set my wits to 
work, or perhaps it was the presence of that wonderful 
comet which was then gracing the morning skies, or 
perhaps, it was the worry over the mortgage in the hopes 
of finding another comet or two to wipe it out. Whatever 
the cause, I had a most wonderful dream. I thought I 
was looking at the sky which was filled with comets, 
long-tailed and short-tailed and with no tails at all. It 
was a marvelous sight, and I had just begun to gather 
in the crop when the alarm clock went off and the 
blessed vision of comets vanished. I took my telescope 
out in the yard and began sweeping the heavens to the 
southwest of the Great Comet in the search for comets. 
Presently I ran upon a very cometary-looking object 
where there was no known nebula. Looking more 
carefully I saw several others in the field of view. Mov- 
ing the telescope about I found that there must have 
been ten or fifteen comets at this point within the space 
of a few degrees. Before dawn killed them out I located 
six or eight of them. 

Undoubtedly Barnard's observations referred to 
ephemeral fragments disrupted from the Comet 
1882 II then in view. 

A great majority of the comets reaching the 
earth's orbit go back to the vast comet cloud, never 
to be identified again. Occasionally, however, a 
comet swings so close to the great planet Jupiter 
that its orbit is bent, and it is "captured" into a 
much shorter period. A "Jupiter capture" has 
I never been directly observed, because most comets 
are still too faint when they reach Jupiter's orbit. 

Nevertheless, about a year ago, astronomers came 
almost as close as they ever will to witnessing the 
aftermath of this remarkable phenomenon. 

In January, 1965, the press reported the dis- 
covery of two new comets by the Chinese, a rather 
unexpected claim inasmuch as it has been cen- 
turies since the Chinese discovered even one comet, 
not to mention two. To everyone's astonishment a 
pair of telegrams eventually reached our Central 
Bureau via England, confirming the existence of 
the objects. At the same time, the Chinese man- 
aged to flout the centuries-old tradition of naming 
comets after their discoverer. In the absence of 
the discoverer's name, our bureau assigned to both 
comets the label Tsuchinshan, which translated 
means "Purple Mountain Observatory." 

Tsuchinshan 1 and Tsuchinshan 2 have re- 
markably similar orbits, whose greatest distances 
from the sun fall near the orbit of Jupiter. As 
these faint comets swung around that distant point 
in 1961, Jupiter was passing in close proximity. 
Quite possibly the gravitational attraction from 
Jupiter secured the capture of a long-period comet 
in that year, simultaneously disrupting it into the 
two Tsuchinshan fragments. However, it is more 
likely that the capture occurred at a somewhat 
earlier pass, a point that will eventually be es- 
tablished by a computer investigation. In any 
event, the observation of a comet pair with such a 
close approach to Jupiter is without precedence 
in the annals of comet history. 

The complete roster of comets for 1965 included 
not only the Tsuchinshan pair, Comet Alcock, 
and the once-in-thirty-three-years visit of Tempel- 
Tuttle, but the recoveries of four other faint 
periodic comets and another new one, Comet 
Klemola, which was accidently picked up during 
a search for faint satellites of Saturn. Of this rich 
harvest, Comet Ikeya-Seki received more attention 
than all the others combined. Day after day, the 
Smithsonian observing stations around the world 
kept a continual photographic watch as the long 
twisted tail developed and faded. These thou- 
sands of frames — an all-time pictorial record — 
may eventually be combined in a film to illustrate 
in motion the details of cometary tail formation. 

By now the Great Comet of 1965 has faded be- 
yond the range of either Ikeya's or Seki's small 
telescope, and has apparently vanished from the 
larger instruments of professional astronomers as 
well. Perhaps in a millennium hence an unsus- 
pecting amateur, never imagining that he has 
caught a sun-grazer, will find it on its next return. 

"When discovered, the comet was only a white 
spot in the moonlit sky," Seki recently wrote to us. 
"I did not even dream that it would later come so 
close to the sun and become so famous." 


The delicate modern version of the Eotvos experiment 
described here shows that the values of inertial mass 
and gravitational mass of an object are equal to within 
one ten-billionth of a percent. Such precision is 
seldom attainable in any area of science. 

17 Gravity Experiments 

R. H. Dicke, P. G. Roll, and J. Weber 

An article from International Science and Technology 
and Modern Science and Technology, 1965. 

In Brief: Meaningful experiments concerning 
the nature of gravity are few and far between — 
for two reasons: gravitational forces are woe- 
fully weak, so data sufficiently precise to be 
meaningful are hard to come by; and the es- 
sential nature of gravity lies hidden in the 
theoretical labyrinth of relativity, in which it's 
easy to lose your way, assuming you have the 
courage to enter in the first place. But to the 
intrepid, three experimental paths lie open. 

The first is in null checks of extreme pre- 
cision — accuracies of 1 part in 10" and a few 
parts in 10* s are involved in two such experi- 
ments discussed here — which seek to balance 
against each other two quantities that are 
expected from existing theory to be equal. The 
magnitude of any inequality discovered sets 
clear limits to theory. A second kind of ex- 
periment seeks more accurate checks than are 
presently available for the three famous pre- 
dictions of Einstein's theory of general rela- 
tivity which ties gravitation to curved space — 
the gravity -induced red shift, bending of light, 
and precession of Mercury's orbit. The third 
experimental approach has generated most in- 
dustrial interest lately, because it see7ns to point 
to the possibilities — remote ones — of communi- 
cation by gravity and of shielding against grav- 
ity. This approach asswnes the existence of 
gravity waves analogous to electromagnetic 
radiation, as predicted by Einstein, and seeks to 
find them.—S.T. 

■ There has been until recently what we might 
term a psychological lull in matters gravita- 
tional. Perhaps this was only to be expected 
after the early great labors in the long history 
of gravity studies. Our present ideas about it 
are most completely crystallized in Newton's 
law of universal gravitation and his three laws 
of motion, and in Einstein's theory of general 
relativity and its modern extensions (see "The 
Dynamics of Space-Time," page 11). Yet this 
lull would be easier for us to understand if 
the field really was "cleaned up" by these 
theoretical achievements. It is not, of course. In 
many fundamental respects gravitation still 
offers all the exploratory challenges of a field 
that's just beginning. 

The feeble force called gravity 

The nature of the challenge and the main 
barrier to possible rewards arises from the fact 
that gravity is the weakest force now known. 
The ratio of the gravitational force to the 
electrostatic force between a proton and an 
electron in an average atom is only about 
5 X 10 -40 . If the diminutive size of this num- 
ber is hard to comprehend, here's another 
analogy that may help. The electrostatic force 
of repulsion between two electrons 5 meters 
apart — a scant 10 -24 dynes — approximately 
equals the gravitational force exerted by the 
entire earth on one of the electrons. The ex- 
tremely small magnitude of gravitational forces 
has led many technical people to feel that, 
while gravitation may be interesting from a 


Gravity Experiments 

philosophical standpoint, it's unimportant either 
theoretically or experimentally in work con- 
cerned with everyday phenomena. This feeling 
may be justified, of course. In fact, on a slightly 
more sophisticated level, application of the 
strong principle of equivalence seems at first to 
reinforce this point of view. 

This principle tells us that the effects of 
gravitational forces on observations can be 
transformed away by making the observations 
in a laboratory framework that is properly ac- 
celerated. The best concrete example of this 
still is Einstein's original freely falling eleva- 
tor in a gravity field, in which an experimenter 
and all his apparatus are placed. Since he and 
his apparatus fall with the same acceleration, 
gravitational effects apparently disappear from 
phenomena observed in the elevator. Gravita- 
tional forces, in other words, sometimes simu- 
late inertial ones. From this it's easy to con- 
clude that gravitation is of little or no concern. 

This is probably too provincial a point of 
view. Our little laboratories are embedded in 
a large universe and thinking scientists can 
hardly ignore this external reality. The uni- 
versal character of gravitation shows that it 
affects all matter, in ways we have yet fully 
to comprehend. For all we know now, gravita- 
tion may play a dominant role in determining 
ultimate particle structure. And our labora- 
tories — freely falling or otherwise — may be 
tossing about on "gravitational waves" with- 
out our knowing it. 

Gravitational waves represent the energy 
which should be radiated from a source — any 
source — composed of masses undergoing ac- 
celerated motion with respect to each other. 
Such waves — if they exist as called for in 
Einstein's theory of general relativity — should 
exert forces on objects with mass, just as elastic 
waves do in passing through an elastic medium, 
or as ocean waves do when striking the shore. 
An athlete exercising with dumbbells or riding 
a bicycle, however, would radiate away an in- 
credibly small amount of such energy. A pair 
of white dwarf stars, on the other hand, with a 
total mass roughly equal to that of the sun, and 
with each star rotating at enormous speed with 
respect to the other in a binary or double-star 
system, might radiate about 2 X 10 87 ergs/sec 
of energy as gravitational waves. This is 5000 
times the amount of energy contained in the 
sun's optical luminosity, and far from negligible 
if it occurs, but in order to decide whether grav- 
ity and gravitational waves are significant or 
not we must learn more about them. And to do 
this we must subject our most profound physi- 
cal theories concerning them to critical scrutiny. 
The moment we do we find that these theories 
rest upon an exceedingly small number of sig- 

nificant experimental measurements, and that 
many of these measurements are of dubious 

Profound theories with shaky foundations 

Einstein's theory of general relativity (usu- 
ally abbreviated by physicists as GTR, to 
distinguish it from many other relativistic 
theories of gravitation) is, of course, the prime 
example. The key idea expressed by the theory, 
relating gravitation to a curvature of space, is 
an elegant one despite the tensor language 
which makes it difficult for many to understand. 
It reduces to the more generally comprehended 
Newtonian form in most cases where measure- 
ments can be made. And further contributions 
to its tacit acceptance by most present-day 
physicists have come from the experimental 
checks of Einstein's three famous predictions 
made on the basis of it: the gravitational red- 
shift of light, the gravitational bending of light, 
and the precession of the perihelion of the orbit 
of the planet Mercury. We have in GTR a 
widely accepted theory, elegant beyond most 
others, based on very little critical evidence. 

Strategy and tactics in experimentation 

How can we remedy this lack? What can the 
earth-bound experimenter do to investigate the 
nature of gravitation? Most often, in view of 
the extreme weakness of the force, he will need 
to use as his power source astronomical bodies 
which have sufficiently strong gravitational 
fields. Instead of a laboratory experiment in 
which all of the significant variables are under 
his control, some or all of the effects he seeks 
may be associated with planetary systems, 
stars, galaxies, or the universe as a whole. Two 
examples of this approach (to which we'll re- 
turn) are the Princeton group's recent refine- 
ment of the classic Eotvos experiment, which 
used the sun as a source of a gravitational field, 
and Weber's suggested study of elastic oscilla- 
tions in the earth, on the idea that they may be 
caused by gravitational waves coming, perhaps, 
from an exploding supernova. 

There are roughly three categories into which 
experiments on gravitation may be placed. First 
and most important are highly precise null ex- 
periments, such as the classic experiment de- 
vised by the Hungarian nobleman and physicist 
Baron von Eotvos. By balancing on a torsion 
balance the inertial forces arising from the 
earth's rotation against gravitational forces due 
to the earth's mass (Fig. 1-1) he was able to 
show to a precision of a few parts in 10* that all 
materials and masses fell with the same accel- 
eration. This was an amazing accuracy for his 
day, and one that two of us (Roll and Dicke) 
have had to work hard for several years to 


Gravity Experiment* 

improve by just two orders of magnitude! Null 
checks of this sort seek to balance against each 
other two quantities, which are expected from 
GTR to be equal or almost equal, in order to 
obtain an upper limit on the magnitude of any 
inequality and thus place clear limits on the 
applicability of the theory. 

The second experimental category seeks to 
improve the accuracy of the three experimental 
verifications of the predictions of GTR men- 
tioned above. These values can and should be 
improved as we'll show later. But limited as 
they are, they do provide valuable insights into 
the kind and number of fields associated with 
the all-pervading force called gravity. 

The third class of experiments deals with 
gravitational radiation. In 1916 Einstein 
studied the approximate solutions of his gravi- 
tational-field equations and concluded that 
gravity waves ought to exist. But only recently 
has it become technologically possible even to 
attempt to detect the minute effects of such 
waves in the laboratory, as is being done by 
the Maryland group with equipment like that 
shown in Fig. 1-2. 

What we've said so far suggests that experi- 
mental programs in gravity and relativity exist 
at only two places — Princeton and Maryland. 
That very nearly is the case. Miscellaneous 
experiments, some highly important, have of 
course been carried out elsewhere; we'll men- 
tion one of them later on. And the air in recent 
years has turned thick with glamorous pro- 
posals for "critical" one-shot experiments. But — 
to our knowledge — no other institutions in the 
world are following a consistent and continuing 
experimental program guided by the rigorous 
theoretical framework which guides our efforts. 

The null-experiment program at Princeton, 
for instance, considers Einstein's GTR as only 
one theory in a large class of relativistic 
theories, any one of which can account for 
gravitational effects equally well with the lim- 
ited, low-quality experimental evidence pres- 
ently available. Our program aims at narrow- 
ing down possibilities in this large class. 

What gravity seems to be 

All relativistic requirements suggest that 
gravitational effects — like electromagnetic ones 
— are due to the interaction of matter with 
one or more of three kinds of classical field. 
(1) Matter could interact with a scalar 
field. Perhaps the most familiar such field is 
the sound field associated with fluctuations in 
air pressure. The air pressure itself is a scalar 
quantity, a number whose value at any point 
is independent of the coordinates used to label 
the point. (2) Matter could interact with a 

Eotvos Experiment 

25-gm masses 


Centrifugal forces 

due to earth's 


Gravitational forces 
due to earth's mass 

Accelerations of masses equal 
to 3 parts in 10 

Princeton Experiment 


Centrifugal forces 

due to earth's revolution 

around Sun 



Accelerations of masses equal 
to 1 part in 10 

Fig. 1-1. The classic Eotvos experiment and the recent 
Princeton version of it that raised its accuracy two 
orders of magnitude, both shown above, prove that all 
masses fall with the same acceleration to within the 
accuracies achieved. This result is necessary — but not 
sufficient by itself — to validate the theory of general 
relativity which ascribes gravitational interactions to 
tensor field interactions in curved space. 

vector field. A familiar three-dimensional ex- 
ample of this is a flowing fluid, in which the 
streaming velocity at each point is a vector 
quantity. (3) Matter could interact with one 
or more tensor fields. The stress distribution 
in an elastic body is one example of a simple 
three-dimensional tensor field. The stress at 
any point in the body has no single value, but 
varies with the direction considered. For this 
reason we must specify six quantities to char- 
acterize the stress at each point. More exactly, 
the scalar, vector, and tensor fields which con- 
cern us are all in four-dimensional space, and 


Gravity Experiments 

Fig. 1-2. Group at the Univer- 
sity of Maryland hopes to de- 
tect oscillations in the gravita- 
tional field reaching earth — 
gravity waves — with the solid 
IVi-ton aluminum cylinder 
shown mounted in the hollow 
cylindrical vacuum chamber. 
Detection cylinder is 2 jt in 
diameter X 6 jt long, and is 
suspended on acoustic bricks to 
null out extraneous vibration. 
Wiring leads to piezo-electric 
quartz sensors embedded in de- 
tector, that convert its oscilla- 
tions to voltages. The hope is 
that ij gravity waves with fre- 
quencies near the natural fre- 
quency of the detector (1657 
cps) impinge upon it, its natural 
frequency will be reinforced. 

they cannot be as readily visualized as in these 
three-dimensional examples. 

In the experimental effort at Princeton we 
hope to eliminate one or more of these four- 
dimensional fields — scalar, vector, and tensor 
— as possible contributors to gravitation. If 
we could demonstrate, for example, that all 
fields could be eliminated except a single ten- 
sor field with suitable properties, Einstein's 
GTR would receive strong support. As of this 
writing, null experiments which have been 
performed at Princeton and other places do 
seem to drastically narrow down the number 
of possible combinations of fields permitted by 
relativistic theories — and hence the possible 
theories themselves — to a smaller class which 
still includes the GTR. Vector fields of any 
appreciable strength, for example, can be ex- 
cluded from the gravitational interaction by 
the Princeton Eotvos experiment. And the same 
experiment appears to exclude more than one 
scalar field from gravitational interactions. 
Arguments based upon another experiment, 
performed by Vernon Hughes and collaborators 
at Yale University, appear to exclude more 
than one tensor field from contributing to 
gravitational interactions. 

Thus, by this unspectacular process of ex- 
perimental elimination, gravitation is being 
increasingly revealed as primarily due to a 
single tensor field, as the GTR requires, al- 
though a substantial contribution from a sca- 
lar field, which some other relativistic theories 
permit, cannot yet be excluded. 

Null experiments don't prove "nothin" 

Of the various null experiments, perhaps the 
most important is the Eotvos experiment con- 

firming that all masses and all materials have 
the same gravitational acceleration. A null re- 
sult is necessary (but not sufficient) for GTR 
(and Newton's law of universal gravitation) 
to be valid. The most precise version of this 
experiment, completed recently at Princeton 
University (Figs. 1-1 and 1-3), showed that the 
acceleration toward the sun of test masses 
of gold and aluminum differs by no more than 
1 part in 10 n , an improvement of two orders 
of magnitude over Eotvos' original experimen- 
tal precision of 3 parts in 10 9 . 

The results of this experiment are highly 
significant for ascertaining that various forms 
of energy (which are related to the inertial 
mass of a body via Einstein's well-known 
formula E = Mc 2 ) are indeed equivalent to 
the gravitational mass of the body. (The gravi- 
tational mass is defined as that property of 
matter on which gravity acts.) To see this, 
consider the energy associated with the strong 
nuclear forces which bind the atomic nuclei of 
our gold and aluminum test masses against 
the disruptive effects of electrostatic repul- 
sive forces. Nuclear binding energy makes up 
11.0 X 10 -3 of the total mass of a gold atom 
and 9.7 X 10~ 3 of the total mass of an alumi- 
num atom. Hence, recalling the accuracy of 1 
part in 10 11 of the new Eotvos experiment, its 
result says that — to within about 1.3 parts in 
10 8 — the gravitational acceleration of the iner- 
tial mass (which is equivalent to nuclear bind- 
ing energy) is the same as the gravitational 
acceleration of all the other mass-energy con- 
tributions to the total masses of gold and 
aluminum. The other contributions come from 
neutrons, protons, electrons, electrostatic en- 
ergy, and other still smaller contributors to 


the total mass of an atom. Moreover, since 
gold and aluminum atoms differ not only in 
nuclear binding energy and total mass, but 
also in many other significant respects — such 
as total electron mass, electron binding energy, 
nuclear electrostatic energy, and energies con- 
centrated in the electron-positron pair field sur- 
rounding the nucleus — similar arguments may 
be advanced to set small upper limits on any 
nonequivalence among all of these different 
forms of energy in their gravitational inter- 

So the Eotvos experiment establishes with 
considerable precision a different form of the 
principle of equivalence than the strong one 
we discussed earlier; it establishes a weak form 
which states that gravitational acceleration is 
the same for all important contributions to the 
mass-energy of a small 'body like an atomic 

But what of the strong version of this same 
principle, upon which GTR is founded? This 
requires that the form and numerical content 
of all physical laws be the same in all freely 
falling, nonrotating laboratories. The more 
precise null result of our Eotvos experiment 
verifies the strong principle of equivalence, too, 
for strongly interacting particles and fields such 
as the electro-magnetic and nuclear-force fields 
and their associated particles, positron-electron 
pairs, and pi mesons. But the experiment fails 
to verify the strong equivalence principle for 
interactions as weak as the universal Fermi 
interaction (involved in the beta decay of 
atomic nuclei) or the gravitational interaction 

Tactics of the Eotvos experiment 

One of the fundamental differences between 
the Princeton experiment and that of Eotvos 
was our use of the gravitational acceleration 
toward the sun, balanced by the corresponding 
centrifugal acceleration due to revolution of 
the earth in orbit about the sun (Fig. 1-1, bot- 
tom). Although these accelerations are some- 
what less than those which Eotvos used — his 
were due to the earth's mass and its rotation 
on its axis, remember — ours had the great ad- 
vantage of appearing with a 24-hour period 
because, in effect, the sun moves around the 
earth once each day. Thus any gravitational 
anomalies on our torsion balance would have 
appeared with a sinusoidal 24-hour periodicity. 
By recording the rotation or torque on our bal- 
ance remotely and continuously, then using a 
digital computer to analyze the record for a 
24-hour periodicity with the proper phase, all 
of the extraneous effects which can produce 
small torques with other periods or the wrong 
phase could be discarded. 

One additional difficulty with which Eotvos 
had to contend was the sensitivity of his tor- 
sion balance to gradients in the gravitational 
field, such as those produced by the good Baron 
himself sitting at the telescope. The Princeton 
experiment minimized such problems not only 
by remote observation (Fig. 1-3) but by mak- 
ing the torsion balance triangular in shape, with 
the two aluminum weights and one gold weight 
suspended from the corners of a triangular 
quartz frame. This threefold symmetry made 
it insensitive to nonuniformities in the gravi- 
tational field. 

Fig. 1-3. The optical-lever sys- 
tem shown here was used to de- 
tect rotation of the triangular 
torsion balance used in Prince- 
ton version of the Eotvos ex- 
periment, shown in Fig. 1-1. 
Output of the detector had to 
be fed back to the torsion bal- 
ance, throvgh an appropriate 
filter network, in order to damp 
out long-period non-gravita- 
tional disturbances of the tor- 
sion balance caused by ground 
vibrations. Because balance i/n.s 
suspended in high-vacu)irti 
chamber (10— % mm) there were 
no natural mechanisms to damp 
such extraneous oscillations in 
periods of time less than several 

Feedback Circuit Feedback electrodes f" 
5 k 4 V 0.5 /iF v ., . I 




r eeuuacr 

IV 0.5 uF v 

Optical-Lever Telescope 


Filter \j> DC output 
Circuit "^ 

Lock-In ^ Reference! 
Amplifier "^ input 


Gravity Experiments 

Our torsion balance evolved to its final form 
over a period of several years, and the final 
data were obtained between July 1962 and 
April 1963 in some 39 runs, lasting from 38 
to 86 hours each. We could detect angular rota- 
tions of about 10 -9 radians, corresponding to a 
torque of about 2.5 X 10~ 10 dyne cm, which 
in turn was 1 X 10~ n times the gravitational 
torque of the sun on one of the balance weights. 
As you may have discerned, we're rather proud 
of our results. They were not easy to get; but 
they buttress our fragile theoretical edifice a 
bit more firmly. 


Arthur Clarke began to think seriously about space 
travel before almost anyone else. His conclusions, 
as seen in the article's very first sentence, are 
somewhat more pessimistic than are now fashionable. 

Space The Unconquerable 

Arthur C. Clarke 

An excerpt from his book Profiles on the Future- 
An Inquiry into the Limits of the Possible, 1958. 

Man will never conquer space. After all that has been 
said in the last two chapters, this statement sounds ludicrous. 
Yet it expresses a truth which our forefathers knew, which we 
have forgotten-and which our descendants must learn again, 
in heartbreak and loneliness. 

Our age is in many ways unique, full of events and phenomena 
which never occurred before and can never happen again. They 
distort our thinking, making us believe that what is true now 
will be true forever, though perhaps on a larger scale. Because 
we have annihilated distance on this planet, we imagine that we 
can do it once again. The facts are far otherwise, and we will 
see them more clearly if we forget the present and turn our 
minds toward the past. 

To our ancestors, the vastness of the Earth was a dominant 
fact controlling their thoughts and lives. In all earlier ages than 
ours, the world was wide indeed and no man could ever see 
more than a tiny fraction of its immensity. A few hundred miles- 
a thousand, at the most-was infinity. Great empires and cultures 
could flourish on the same continent, knowing nothing of each 
other's existence save fables and rumors faint as from a distant 
planet. When the pioneers and adventurers of the past left 
their homes in search of new lands, they said good-by forever 


Space The Unconquerable 

to the places of their birth and the companions of their youth. 
Only a lifetime ago, parents waved farewell to their emigrating 
children in the virtual certainty that they would never meet again. 
And now, within one incredible generation, all this has 
changed. Over the seas where Odysseus wandered for a decade, 
the Rome-Beirut Comet whispers its way within the hour. And 
above that, the closer satellites span the distance between Troy 
and Ithaca in less than a minute. 

Psychologically as well as physically, there are no longer any 
remote places on Earth. When a friend leaves for what was once 
a far country, even if he has no intention of returning, we can- 
not feel that same sense of irrevocable separation that saddened 
our forefathers. We know that he is only hours away by jet 
liner, and that we have merely to reach for the telephone to hear 
his voice. And in a very few years, when the satellite communica- 
tion network is established, we will be able to see friends on the 
far side of the Earth as easily as we talk to them on the other 
side of the town. Then the world will shrink no more, for it 
will have become a dimensionless point. 

But the new stage that is opening up for the human drama 
will never shrink as the old one has done. We have abolished 
space here on the little Earth; we can never abolish the space 
that yawns between the stars. Once again, as in the days when 
Homer sang, we are face to face with immensity and must ac- 
cept its grandeur and terror, its inspiring possibilities and its 
dreadful restraints. From a world that has become too small, 
we are moving out into one that will be forever too large, whose 
frontiers will recede from us always more swiftly than we can 
reach out toward them. 

Consider first the fairly modest solar, or planetary, distances 
which we are now preparing to assault. The very first Lunik 
made a substantial impression upon them, traveling more than 
two hundred million miles from Earth-six times the distance to 
Mars. When we have harnessed nuclear energy for space flight, 
the solar system will contract until it is little larger than the 


Earth today. The remotest of the planets will be perhaps no 
more than a week's travel from Earth, while Mars and Venus 
will be only a few hours away. 

This achievement, which will be witnessed within a century, 
might appear to make even the solar system a comfortable, 
homely place, with such giant planets as Saturn and Jupiter 
playing much the same role in our thoughts as do Africa or Asia 
today. (Their qualitative differences of climate, atmosphere, and 
gravity, fundamental though they are, do not concern us at the 
moment.) To some extent this may be true, yet as soon as we 
pass beyond the orbit of the Moon, a mere quarter-million miles 
away, we will meet the first of the barriers that will sunder 
Earth from her scattered children. 

The marvelous telephone and television network that will 
soon enmesh the whole world, making all men neighbors, can- 
not be extended into space. It will never be possible to converse 
with anyone on another planet. 

Do not misunderstand this statement. Even with today's radio 
equipment, the problem of sending speech to the other planets 
is almost trivial. But the messages will take minutes— sometimes 
hours— on their journey, because radio and light waves travel at 
the same limited speed of 186,000 miles a second. Twenty years 
from now you will be able to listen to a friend on Mars, but 
the words you hear will have left his mouth at least three 
minutes earlier, and your reply will take a corresponding time 
to reach him. In such circumstances, an exchange of verbal mes- 
sages is possible— but not a conversation. Even in the case of the 
nearby Moon, the two-and-a-half second time lag will be an- 
noying. At distances of more than a million miles, it will be 

To a culture which has come to take instantaneous communica- 
tion for granted, as part of the very structure of civilized life, 
this "time barrier" may have a profound psychological impact. 
It will be a perpetual reminder of universal laws and limitations 
against which not all our technology can ever prevail. For it 


Space The Unconquerable 

seems as certain as anything can be that no signal-still less 
any material object-can ever travel faster than light. 

The velocity of light is the ultimate speed limit, being part of 
the very structure of space and time. Within the narrow confines 
of the solar system, it will not handicap us too severely, once 
we have accepted the delays in communication which it in- 
volves. At the worst, these will amount to eleven hours— the 
time it takes a radio signal to span the orbit of Pluto, the outer- 
most planet. Between the three inner worlds Earth, Mars, and 
Venus, it will never be more than twenty minutes— not enough 
to interfere seriously with commerce or administration, but 
more than sufficient to shatter those personal finks of sound or 
vision that can give us a sense of direct contact with friends on 
Earth, wherever they may be. 

It is when we move out beyond the confines of the solar 
system that we come face to face with an altogether new order 
of cosmic reality. Even today, many otherwise educated men- 
like those savages who can count to three but lump together all 
numbers beyond four— cannot grasp the profound distinction 
between solar and stellar space. The first is the space enclos- 
ing our neighboring worlds, the planets; the second is that which 
embraces those distant suns, the stars. And it is literally millions 
of times greater. 

There is no such abrupt change of scale in terrestrial affairs. 
To obtain a mental picture of the distance to the nearest star, 
as compared with the distance to the nearest planet, you must 
imagine a world in which the closest object to you is only 
five feet away— and then there is nothing else to see until you 
have traveled a thousand miles. 

Many conservative scientists, appalled by these cosmic gulfs, 
have denied that they can ever be crossed. Some people never 
learn; those who sixty years ago scoffed at the possibility of 
flight, and ten (even five!) years ago laughed at the idea of 
travel to the planets, are now quite sure that the stars will always 
be beyond our reach. And again they are wrong, for they have 


failed to grasp the great lesson of our age— that if something is 
possible in theory, and no fundamental scientific laws oppose its 
realization, then sooner or later it will be achieved. 

One day— it may be in this century, or it may be a thousand 
years from now— we shall discover a really efficient means of 
propelling our space vehicles. Every technical device is always 
developed to its limit (unless it is superseded by something 
better) and the ultimate speed for spaceships is the velocity of 
light. They will never reach that goal, but they will get very 
close to it. And then the nearest star will be less than five 
years' voyaging from Earth. 

Our exploring ships will spread outward from their home over 
an ever-expanding sphere of space. It is a sphere which will 
grow at almost— but never quite— the speed of light. Five years 
to the triple system of Alpha Centauri, ten to that strangely 
matched doublet Sirius A and B, eleven to the tantalizing enigma 
of 61 Cygni, the first star suspected of possessing a planet. These 
journeys are long, but they are not impossible. Man has always 
accepted whatever price was necessary for his explorations and 
discoveries, and the price of space is time. 

Even voyages which may last for centuries or millenniums 
will one day be attempted. Suspended animation, an undoubted 
possibility, may be the key to interstellar travel. Self-contained 
cosmic arks which will be tiny traveling worlds in their own 
right may be another solution, for they would make possible 
journeys of unlimited extent, lasting generation after generation. 
The famous time dilation effect predicted by the theory of rela- 
tivity, whereby time appears to pass more slowly for a traveler 
moving at almost the speed of light, may be yet a third. 1 And 
there are others. 

With so many theoretical possibilities for interstellar flight, 
we can be sure that at least one will be realized in practice. 
Remember the history of the atomic bomb; there were three 


Space The Unconquerable 

different ways in which it could be made, and no one knew 
which was best. So they were all tried-and they all worked. 

Looking far into the future, therefore, we must picture a 
slow (little more than half a billion miles an hour!) expansion 
of human activities outward from the solar system, among the 
suns scattered across the region of the Galaxy in which we now 
find ourselves. These suns are on the average five light-years 
apart; in other words, we can never get from one to the next 
in less than five years. 

To bring home what this means, let us use a down-to-earth 
analogy. Imagine a vast ocean, sprinkled with islands— some 
desert, others perhaps inhabited. On one of these islands an 
energetic race has just discovered the art of building ships. It is 
preparing to explore the ocean, but must face the fact that the 
very nearest island is five years' voyaging away, and that no pos- 
sible improvement in the technique of shipbuilding will ever 
reduce this time. 

In these circumstances (which are those in which we will 
soon find ourselves) what could the islanders achieve? After a 
few centuries, they might have established colonies on many of 
the nearby islands, and have briefly explored many others. The 
daughter colonies might themselves have sent out further pio- 
neers, and so a kind of chain reaction would spread the original 
culture over a steadily expanding area of the ocean. 

But now consider the effects of the inevitable, unavoidable 
time lag. There could be only the most tenuous contact between 
the home island and its offspring. Returning messengers could 
report what had happened on the nearest colony— five years ago. 
They could never bring information more up to date than that, 
and dispatches from the more distant parts of the ocean would 
be from still further in the past— perhaps centuries behind the 
times. There would never be news from the other islands, but 
only history. 

No oceanic Alexander or Caesar could ever establish an em- 
pire beyond his own coral reef; he would be dead before his 


orders reached his governors. Any form of control or adminis- 
tration over other islands would be utterly impossible, and all 
parallels from our own history thus cease to have any meaning. 
It is for this reason that the popular science-fiction stories of 
interstellar empires and intrigues become pure fantasies, with no 
basis in reality. Try to imagine how the War of Independence 
would have gone if news of Bunker Hill had not arrived in 
England until Disraeli was Victoria's prime minister, and his 
urgent instructions on how to deal with the situation had reached 
America during President Eisenhower's second term. Stated in 
this way, the whole concept of interstellar administration or cul- 
ture is seen to be an absurdity. 

All the star-borne colonies of the future will be independent, 
whether they wish it or not. Their liberty will be inviolably 
protected by time as well as space. They must go their own way 
and achieve their own destiny, with no help or hindrance from 
Mother Earth. 

At this point, we will move the discussion on to a new level 
and deal with an obvious objection. Can we be sure that the 
velocity of light is indeed a limiting factor? So many "impas- 
sable" barriers have been shattered in the past; perhaps this 
one may go the way of all the others. 

We will not argue the point, or give the reasons scientists 
believe that light can never be outraced by any form of radiation 
or any material object. Instead, let us assume the contrary and 
see just where it gets us. We will even take the most optimistic 
possible case, and imagine that the speed of transportation may 
eventually become infinite. 

Picture a time when, by the development of techniques as 
far beyond our present engineering as a transistor is beyond a 
stone ax, we can reach anywhere we please instantaneously, with 
no more effort than by dialing a number. This would indeed cut 
the universe down to size, and reduce its physical immensity to 
nothingness. What would be left? 

Everything that really matters. For the universe has two 


Space The Unconquerable 

aspects— its scale, and its overwhelming, mind-numbing com- 
plexity. Having abolished the first, we are now face-to-face with 
the second. 

What we must now try to visualize is not size, but quantity. 
Most people today are familiar with the simple notation which 
scientists use to describe large numbers; it consists merely of 
counting zeros, so that a hundred becomes 10 2 , a million, 10 6 ; a 
billion, 10 9 and so on. This useful trick enables us to work with 
quantities of any magnitude, and even defense budget totals 
look modest when expressed as $5.76 x 10 9 instead of $5,760,- 

The number of other suns in our own Galaxy (that is, the 
whirlpool of stars and cosmic dust of which our Sun is an 
out-of-town member, lying in one of the remoter spiral arms) is 
estimated at about 10 u -or written in full, 100,000,000,000. Our 
present telescopes can observe something like 10 9 other galaxies, 
and they show no sign of thinning out even at the extreme limit 
of vision. There are probably at least as many galaxies in the 
whole of creation as there are stars in our own Galaxy, but let 
us confine ourselves to those we can see. They must contain a 
total of about 10 u times 10 9 stars, or 10 20 stars altogether. 

One followed by twenty other digits is, of course, a number 
beyond all understanding. There is no hope of ever coming to 
grips with it, but there are ways of hinting at its implications. 

Just now we assumed that the time might come when we 
could dial ourselves, by some miracle of matter transmission, 
effortlessly and instantly round the cosmos, as today we call a 
number in our local exchange. What would the cosmic telephone 
directory look like if its contents were restricted to suns and 
it made no effort to list individual planets, still less the millions 
of places on each planet? 

The directories for such cities as London and New York are 
already getting somewhat out of hand, but they list only about 
a million— 10 6 — numbers. The cosmic directory would be 10 14 


times bigger, to hold its 10 20 numbers. It would contain more 
pages than all the books that have ever been produced since 
the invention of the printing press. 

To continue our fantasy a little further, here is another con- 
sequence of twenty-digit telephone numbers. Think of the pos- 
sibilities of cosmic chaos, if dialing 27945015423811986385 
instead of 27945015243811986385 could put you at the wrong 
end of Creation. . . . This is no trifling example; look well and 
carefully at these arrays of digits, savoring their weight and 
meaning, remembering that we may need every one of them to 
count the total tally of the stars, and even more to number their 

Before such numbers, even spirits brave enough to face the 
challenge of the light-years must quail. The detailed examination 
of all the grains of sand on all the beaches of the world is a 
far smaller task than the exploration of the universe. 

And so we return to our opening statement. Space can be 
mapped and crossed and occupied without definable limit; but it 
can never be conquered. When our race has reached its ultimate 
achievements, and the stars themselves are scattered no more 
widely than the seed of Adam, even then we shall still be like 
ants crawling on the face of the Earth. The ants have covered 
the world, but have they conquered it— for what do their count- 
less colonies know of it, or of each other? 

So it will be with us as we spread outward from Mother 
Earth, loosening the bonds of kinship and understanding, hear- 
ing faint and belated rumors at second— or third— or thousandth- 
hand of an ever-dwindling fraction of the entire human race. 
Though Earth will try to keep in touch with her children, in 
the end all the efforts of her archivists and historians will be 
defeated by time and distance, and the sheer bulk of material. 
For the number of distinct societies or nations, when our race 
is twice its present age, may be far greater than the total num- 
ber of all the men who have ever lived up to the present time. 


Space The Unconquerable 

We have left the realm of comprehension in our vain effort 
to grasp the scale of the universe; so it must always be, sooner 
rather than later. 

When you are next out of doors on a summer night, turn your 
head toward the zenith. Almost vertically above you will be 
shining the brightest star of the northern skies— Vega of the 
Lyre, twenty-six years away at the speed of light, near enough 
the point-of -no-return for us short-lived creatures. Past this blue- 
white beacon, fifty times as brilliant as our sun, we may send our 
minds and bodies, but never our hearts. 

For no man will ever turn homeward from beyond Vega to 
greet again those he knew and loved on Earth. 


Many scientists have argued recently that intelligent 
life may be quite common in the universe. This work 
was originally written by Shklovskii, in Russian, and 
the "Annotations, additions, and discussions" which 
Sagan has added are bracketed by the symbols V and A 

19 Is There Intelligent Life Beyond the Earth? 

I. S. Shklovskii and Carl Sagan 


An excerpt from Intelligent Life in the Universe, 1966. 

V ¥ n the last two chapters, we have seen that the prospects for interstellar com- 
munication over distances of some tens of light years seem reasonable; over 
hundreds of light years, more difficult; and over thousands of light years, only 
possibly by civilizations in substantial advance of our own. If it seemed likely that 
technical civilizations existed on planets only 10 or 20 light years away, or civiliza- 
tions greatly in advance of our own, at larger distances, a serious effort to establish 
contact might be justified. On the other hand, if we can only reasonably expect 
civilizations at about our level of technical advance thousands of light years away, 
attempts at communication would not seem profitable, at least at the present time. 
In the present chapter, we shall make some effort to compute the number of extant 
technical civilizations in the Galaxy, which will permit us to estimate the average 
distances between civilizations. To perform such estimates, we must select 
numerical values for quantities which are extremely poorly known, such as the 
average lifetime of a technical civilization. The reliability of our answers will 
reflect this uncertainty. A The analysis will have an exclusively probabilistic 
character, V and the reader is invited to make his own estimate of the numerical 
values involved, and to draw his own conclusions on the numbers of advanced 
technical civilizations in the Galaxy. A However, these analyses are of undoubted 
methodological interest and illustrate very well the potentialities and limitations of 
this type of investigation. 

V We shall be concerned with two general approaches: first, a simple 
discussion due essentially to Frank Drake, and then a more elaborate treatment due 
to the German astronomer Sebastian von Hoerner, when he was working at the 
National Radio Astronomy Observatory, Green Bank, West Virginia. 

V We desire to compute the number of extant Galactic communities which 
have attained a technical capability substantially in advance of our own. At the 
present rate of technological progress, we might picture this capability as several 
hundred years or more beyond our own stage of development. A simple method of 
computing this number, N, was discussed extensively at a conference on intelligent 
extraterrestrial life, held at the National Radio Astronomy Observatory in Novem- 
ber, 1961, and sponsored by the Space Science Board of the National Academy of 
Sciences. Attending this meeting were D. W. Atchley, Melvin Calvin, Giuseppe 
Cocconi, Frank Drake, Su-Shu Huang, John C. Lilley, Philip M. Morrison, Ber- 
nard M. Oliver, J. P. T. Pearman, Carl Sagan, and Otto Struve. While the details 
differ in several respects, the following discussion is in substantial agreement with 
the conclusions of the conference. 

V The number of extant advanced technical civilizations possessing both the 
interest and the capability for interstellar communication can be expressed as 


Is There Intelligent Life Beyond the Earth? 

N = RtfaefififcL 

R* is the mean rate of star formation, averaged over the lifetime of the Galaxy; f p is 
the fraction of stars with planetary systems; n c is the mean number of planets in 
each planetary system with environments favorable for the origin of life; /, is the 
fraction of such favorable planets on which life does develop; U is the fraction of 
such inhabited planets on which intelligent life with manipulative abilities arises 
during the lifetime of the local sun; f c is the fraction of planets populated by 
intelligent beings on which an advanced technical civilization in the sense previously 
defined arises, during the lifetime of the local sun; and L is the lifetime of the 
technical civilization. We now proceed to discuss each parameter in turn. 

V Since stars of solar mass or less have lifetimes on the main sequence 
comparable to the age of the Galaxy, it is not the present rate of star formation, but 
the mean rate of star formation during the age of the Galaxy which concerns us 
here. The number of known stars in the Galaxy is ~ 10 n , most of which have 
masses equal to or less than that of the Sun. The age of the Galaxy is ~ 10 10 years. 
Consequently, a first estimate for the mean rate of star formation would be — 10 
stars yr -1 . The present rate of star formation is at least an order of magnitude less 
than this figure, and according to the Dutch-American astronomer Maarten 
Schmidt, of Mt. Wilson and Palomar Observatories, the rate of star formation in 
early Galactic history is possibly several orders of magnitude greater. According to 
present views of element synthesis in stars, discussed in Chapter 8, those stars and 
planets formed in the early history of the Galaxy must have been extremely poor in 
heavy elements. Technical civilizations developed on such ancient planets would of 
necessity be extremely different from our own. But in the flurry of early star 
formation, when the Galaxy was young, heavy elements must have been generated 
rapidly, and later generations of stars and planets would have had adequate 
endowments of the heavy elements. These very early systems should be subtracted, 
from our estimate of /?*. On the other hand, there are probably vast numbers of 
undetected low-mass stars whose inclusion will tend to increase our estimate of /?*. 
For present purposes, we adopt R* — 10 stars yr" 1 . 

V From the frequencies of dark companions of nearby stars, from the 
argument on stellar rotation, and from contemporary theories of the origin of the 
solar system [see Chapters 11-13], we have seen that planets seem to be a very 
common, if not invariable, accompaniment to main sequence stars. We therefore 
adopt / p — 1 . 

V In Chapter 1 1 , we saw that even many multiple star systems may have 
planets in sufficiently stable orbits for the origin and development of life. In our 
own solar system, the number of planets which are favorably situated for the origin 
of life at some time or another is at least one, probably two, and possibly three or 
more [see Chapters 16, 19, 20, and 23]. We expect main sequence stars of 
approximately solar spectral type — say, between F2 and K5 — to have a similar 
distribution of planets, and for such stars, we adopt n e — 1 . However, the bulk of 
the main sequence stars — well over 60 percent — are M stars; as we mentioned in 


Chapter 24, if the planets of these suns are distributed with just the same spacings 
as the planets of our Sun, even the innermost will be too far from its local sun to be 
heated directly to temperatures which we would consider clement for the origin and 
evolution of life. However, it is entirely possible that such lower-luminosity stars 
were less able to clear their inner solar systems of nebular material from which the 
planets were formed early in their history. Further, the greenhouse effect in 
Jovian-type planets of M stars should produce quite reasonable temperatures. We 
therefore tentatively adopt for main sequence stars in general n c — 1. 

V In Chapters 14-17, we discussed the most recent work on the origin of life 
on Earth, which suggests that life arose very rapidly during the early history of the 
Earth. We discussed the hypothesis that the production of self-replicating 
molecular systems is a forced process which is bound to occur because of the 
physics and chemistry of primitive planetary environments. Such self-replicating 
systems, with some minimal control of their environments and situated in a medium 
filled with replication precursors, satisfy all the requirements for natural selection 
and biological evolution. Given sufficient time and an environment which is not 
entirely static, the evolution of complex organisms is, in this view, inevitable. The 
finding of even relatively simple life forms on Mars or other planets within our solar 
system would tend to confirm this hypothesis. In our own solar system, the origin 
of life has occurred at least once, and possibly two or more times. We adopt 

V The question of the evolution of intelligence is a difficult one. This is not a 
field which lends itself to laboratory experimentation, and the number of intelligent 
species available for study on Earth is limited. In Chapter 25, we alluded to some 
of the difficulties of this problem. Our technical civilization has been present for 
only a few billion ths of geological time; yet it has arrived about midway in the 
lifetime of our Sun on the main sequence. The evolution of intelligence and 
manipulative abilities has resulted from the product of a large number of 
individually unlikely events. On the other hand, the adaptive value of intelligence 
and of manipulative ability is so great — at least until technical civilizations are 
developed — that if it is genetically feasible, natural selection seems likely to bring it 

V The American physiologist John C. Lilley, of the Communication Research 
Institute, Coral Gables, Florida, has argued that the dolphins and other cetacea 
have surprisingly high levels of intelligence. Their brains are almost as large as 
those of human beings. These brains are as convoluted as our brains, and their 
neural anatomy is remarkably similar to that of the primates, although the most 
recent common ancestor of the two groups lived more than 100 million years ago. 
Dolphins are capable of making a large number of sounds of great complexity, 
which are almost certainly used for communication with other dolphins. The most 
recent evidence suggests that they are capable of counting, and can mimic human 
speech. Large numbers of anecdotes supposedly illustrating great intelligence in 
the dolphins have been recorded, from the time of Pliny to the present. The 
detailed study of dolphin behavior and serious attempts to communicate with them 


Is There Intelligent Life Beyond the Earth? 

are just beginning and hold out the possibility that some day we will be able to 
communicate, at least at a low level, with another intelligent species on our planet. 
Dolphins have very limited manipulative abilities, and despite their apparent level 
of intelligence, could not have developed a technical civilization. But their 
intelligence and communicativeness strongly suggest that these traits are not limited 
to the human species. With the expectation that the Earth is not unique as the 
abode of creatures with intelligence and manipulative abilities, but also allowing for 
the fact that apparently only one such species has developed so far in its history, 
and this only recently, we adopt /, — 10" 1 . 

V The present technical civilization of the planet Earth can be traced from 
Mesopotamia to Southeastern Europe, to Western and Central Europe, and then to 
Eastern Europe and North America. Suppose that somewhere along the tortuous 
path of cultural history, an event had differed. Suppose Charles Martel had not 
stopped the Moors at Tours in 732 a.d. Suppose Ogdai had not died at Karakorum 
at the moment that Subutai's Mongol armies were entering Hungary and Austria, and 
that the Mongol invasion had swept through the non-forested regions of western Eu- 
rope. Suppose the classical writings of Greek and Roman antiquity had not been pre- 
served through the Middle Ages in African mosques and Irish monasteries. There are 
a thousand "supposes." Would Chinese civilization have developed a technical 
civilization if entirely insulated from the West? Would Aztec civilization have de- 
veloped a technical phase had there been no conquistadores? Recorded history, even 
in mythological guise, covers less than 10"- of the period in which the Earth has been 
inhabited by hominids, and less than about 10~ 5 of geological time. The same 
considerations are involved here as in the determination of /*. The development of 
a technical civilization has high survival value at least up to a point; but in any 
given case, it depends on the concatenation of many improbable events, and it has 
occurred only recently in terrestrial history. It is unlikely that the Earth is very 
extraordinary in possessing a technical civilization, among planets already inhabited 
by intelligent beings. As before, over stellar evolutionary timescales, we adopt 

/c~ 10 1 . 

V The multiplication of the preceding factors gives N = 10 x 1 X 1 xl X 
10" 1 x 10" 1 x L = 10' 1 x L. L is the mean lifetime in years of a technical 
civilization possessing both the interest and the capability for interstellar com- 
munication. For the evaluation of L there is — fortunately for us, but unfortunately 
for the discussion — not even one known terrestrial example. The present tech- 
nical civilization on Earth has reached the communicative phase (in the sense 
of high-gain directional antennas for the reception of extraterrestrial radio signals) 
only within the last few years. There is a sober possibility that L for Earth will 
be measured in decades. On the other hand, it is possible that international po- 
litical differences will be permanently settled, and that L may be measured in 
geological time. It is conceivable that on other worlds, the resolution of national 
conflicts and the establishment of planetary governments are accomplished before 
weapons of mass destruction become available. We can imagine two extreme 
alternatives for the evaluation of L: (a) a technical civilization destroys itself soon 


after reaching the communicative phase (L less than 10 2 years); or (b) a technical 
civilization learns to live with itself soon after reaching the communicative phase. 
If it survives more than 10" years, it will be unlikely to destroy itself afterwards. In 
the latter case, its lifetime may be measured on a stellar evolutionary timescale (L 
much greater than 10 8 years). Such a society will exercise self-selection on its 
members. The slow, otherwise inexorable genetic changes which might in one of 
many ways make the individuals unsuited for a technical civilization could be 
controlled. The technology of such a society will certainly be adequate to cope 
with geological changes, although its origin is sensitively dependent on geology. 
Even the evolution of the local sun through the red giant and white dwarf 
evolutionary stages may not pose insuperable problems for the survival of an 
extremely advanced community. 

V It seems improbable that surrounded by large numbers of flourishing and 
diverse galactic communities, a given advanced planetary civilization will retreat 
from the communicative phase. This is one reason that L itself depends on N. 
Von Hoerner has suggested another reason: He feels that the means of avoiding 
self-destruction will be among the primary contents of initial interstellar communi- 
cations. If N is large, the values of /,, f if and f r may also be larger as a result. In 
Chapter 15, we mentioned the possibility of the conscious introduction of life into 
an otherwise sterile planet by interstellar space travelers. In Chapter 33, below, we 
shall discuss the possibility that such interstellar space travelers might also affect the 
value of f c . 

V Our two choices for L — < 10 2 years, and >> 10 8 years — lead to two 
values for N: less than ten communicative civilizations in the Galaxy; or many more 
than 10 7 . In the former case, we might be the only extant civilization; in the latter 
case, the Galaxy is filled with them. The value of N depends very critically on 
our expectation for the lifetime of an average advanced community. It seems 
reasonable to me that at least a few percent of the advanced technical civilizations 
in the Galaxy do not destroy themselves, nor lose interest in interstellar communi- 
cation, nor suffer insuperable biological or geological catastrophes, and that their 
lifetimes, therefore, are measured on stellar evolutionary timescales. As an average 
for all technical civilizations, both short-lived and long-lived, I adopt L — 10 7 
years. This then yields as the average number of extant advanced technical 
civilizations in the Galaxy 

N ~ 10 6 . 

Thus, approximately 0.001 percent of the stars in the sky will have a planet upon 
which an advanced civilization resides. The most probable distance to the nearest 
such community is then several hundred light years. (In the Space Science Board 
Conference on Intelligent Extraterrestrial Life, previously mentioned, the individual 
values of N selected lay between 10* and 10 ;> civilizations. The corresponding 
range of distances to the nearest advanced community is then between ten and 
several thousands of light years.) A 



The table on the facing page lists only those stars within 
twenty-two light years of the earth that have probabilities for 
the existence of planets which could support human life. 
The reader with astronomical interests should scan books on 
astronomy for a detailed explanation of most of the 
terminology used in this table. 

The Stars Within Twenty-Two Light Years 
That Could Have Habitable Planets 

Stephen H. Dole 

An excerpt from his book Habitable Planets for Man, 1964. 


^ r~- r^i so r-- t — v© m ^ ^. r~ r^r^ — 

do © ~~ w *"" w d^"^" w w ~ d d^ddd'd d~~~ "^"^ddd i 


Tf«d<o^M'~'d3 > '0<»d»ddd«^ , JM>c*'0^ , '3 


1 W o^ 1 o* d !> d oc ^ o* t] m sd o^ r-' i-* *c 

mnnoo- — fir-^OfNvCON^f — 9innOONNNN*«»NNN*pNN<N*0;''. f oc O O O 
rt 4 x d -• — — ' — rjri(NTtfl->AvCvdr^i s --odocxxododwo6xO*^^0'6oddoO — — — c-i rvj cs| 

»-' v 'NiflXvi N- »On M nm-_„ < ! 0vr i_ i CNi-Or-OOf2-N^a,O^_mNMNn 


— oo oo oo oo cm t-M wi 

o o o o o 


u-i Tf TT 


>o >c t 

— a^^^c^w^^^ooooorn 
\Ow"> — — -- © Os6oo6oooor~r~r-c~c~r~~ 
r-r-nnnri(Nn(SMNN(N<NrN — - .____ ____-. — — — — — — ——— — — — — — 


r~ f-"> «o \C -rt 00 

f*> VO 00 VC 

m m tj- 
i/-> ir> rv| rsi so 

t> x 'f * fi 

m r^ oo vo 

! oo 

Tf 00 


• 00 

00 00 

v, oo o*> r-- Tt 


^■m^^so — — o* 

r>-ONr-h-r>--oox^O«(NNNiNr»r^ooi s '^h-(NMN'n 

<ri«rioooo<nTM' s - , 00o<o 

r» vo ^o ^ - — 

i i i i ' ' _1 _l_ _L I I I I I I I I ^- 

+ + I + I I I I + I + + 

+ + + I I 

+ + ' + + + I I I + + 



- — — 00 '" ' 

o\ o v-> — 










— •<* 

(N «-> 



Tt 1/1 

r- m 




O l-~ 

O O* 




m Cl 

i/-i rt 



1 1 

+ 1 






oa u 



— _ \o 


3 00 to 

< DQ < 

•a >-, >^ 

; _ &. '— oo 

o '-g -g -5 -5 .9 -g -g -g < < « ,,££-■ 

a. a. o-T 

Tf N (N sO C 

r- en m «■*, rt 
r T3 

m < m 

m .- .- < 


■* ^i * °^ 

-N» ao.5 K « u-O- o-t- i/i in > • ■ ^ •*» 

L-LJ._ . ,_ -- ^-' W ^C^CSC — — — l_l__i_-T-J_ 

_ LL) Li. & 
+ O.Q.I 


The evidence concerning Unidentified Flying Objects is 
carefully examined in this government-sponsored study. 

21 Scientific Study of Unidentified Flying Objects 

Edward U. Condon and Walter Sullivan 

An excerpt from this title based on the work of a government-sponsored 
research project, 1969. 


If, as many people suspect, our planet is being visited clan- 
destinely by spacecraft, manned or controlled by intelligent 
creatures from another world, it is the most momentous devel- 
opment in human history. 

Opinion surveys indicate that several million Americans 
believe they have seen objects that could be described as un- 
identified flying objects (UFOs), or "flying saucers." What, in 
fact, have they seen? 

It appears that the Central Intelligence Agency, in 1953, 
was party to a scheme to "debunk" the UFOs. (The previous- 
ly-secret document relating to this proposal is Appendix U in 
this book.) Has the government, in fact, been aware for some 
years that earth was under surveillance and has there been an 
effort to avoid panic by concealing the fact? 

Or has the Air Force, in fulfilling its responsioility to deny 
our skies to hostile vehicles, been too lax to recognize the 
threat? Project Blue Book, the Air Force office responsible for 
assembling UFO reports at Wright-Patterson Air Force Base 
near Dayton, Ohio, is a low-priority operation, long manned 
by one officer, a sergeant and secretary. 

In 1966 rumblings of discontent, both on Capitol Hill and 
among the public at large, led the Air Force to seek an inde- 
pendent assessment of the situation. It was a remarkable fact 
that, despite the enormous public interest in UFOs, the big 
guns of science had never been brought to bear on the problem. 

Now for the first time a full-fledged scientific study has been 
carried out. Over a two-year period hundreds of cases were 
investigated. Case studies on 59 of the most important or most 
representative are presented in this report. Of these, ten relate 
to incidents that occurred before the project but were suffi- 
ciently well documented to merit pursuit. 

A number of alleged UFO photographs have been analyzed 
in depth, with measurements being made at the scenes where 
the photographs were taken and of the film itself. Some have 
been explained, but at least one, showing a disk-shaped object 
in flight over Oregon, (plates 23 through 26), is classed as 
difficult to explain in a conventional way. 

The study, at a cost of about half a million dollars, was 
carried out by the University of Colorado under the direction 
of Dr. Edward U. Condon. He was clearly chosen, not only 


Scientific Study of Unidentified Flying Objects 

because of his scientific eminence, but because of his unques- 
tionable independence. He has served as President of the 
American Association for the Advancement of Science, the 
American Physical Society and as head of the National Bureau 
of Standards. The latter operated a complex of laboratories in 
Boulder, home of the University of Colorado. They now 
come under the recently-created Environmental Science Serv- 
ices Administration. Also in Boulder, on a mesa overlooking 
the town, is the National Center for Atmospheric Research. 
These centers offered Dr. Condon a wide range of experts in 
many fields of science. 

Dr. Condon has the build of a football halfback. In his mid- 
sixties, he is a bit old for the game. Nevertheless, as the reader 
will see in this report, he has a tendency in scientific matters 
to lower his knowledgeable head and charge the line. 

His independence has been many times demonstrated in his 
support of liberal (and sometimes unpopular) causes. He was 
one of the few who tangled with the House Committee on 
Un-American Activities and, to all intents and purposes, came 
out on top. Richard M. Nixon was associated with attempts to 
challenge his security clearance, and early in 1969 the Air 
Force, mindful that little love was lost between the two men, 
clearly wanted to get the Condon Report out of the way be- 
fore Nixon became President. 

The report concludes that there is no evidence to justify a 
belief that extraterrestrial visitors have penetrated our skies 
and not enough evidence to warrant any further scientific in- 
vestigation. As Condon himself anticipated, this will not 
gladden UFO enthusiasts. There is no question but that a great 
many people want to believe the extraterrestrial hypothesis. 

Why they do so is beyond the scope of the report — or this 
introduction. The feeling has been attributed to a hope that 
some sort of superior beings are watching over our world, 
prepared to intervene if things get too bad. Some people, too, 
are suspicious of "The Establishment" or resentful of what 
seems to them arrogant disregard by scientists of "evidence" 
for the existence of UFOs. 

Although people have been reporting "flying saucers" for 
more than 20 years, there has been no machinery for bringing 
to bear on such sightings the many techniques for objective 
analysis available to modern science. When a citizen saw a 
UFO he tended to call the police who, in many cases, had no 
idea what to do about it. Those who knew that the nearest Air 
Force base was responsible for investigating such reported in- 
trusions into American air space often found that the man at 
the base assigned to such duty was preoccupied with other 

Some private organizations of concerned citizens, notably 
the National Investigations Committee for Aerial Phenomena 
(NICAP) and the Aerial Phenomena Research Organization 
(APRO) did the best they could. However, their resources 
were limited and they were handicapped, particularly in their 
dealings with government agencies, by their unofficial status 


and the fact that their membership consisted largely of people 
sympathetic to the view that UFOs may be controlled by an 
alien civilization (the so-called ETI, or Extra-Terrestrial In- 
telligence, hypothesis). 

For the University of Colorado study, experts in radar, in 
plasma physics, in mirages, in photographic analysis and 
problems of perception were called in. Upon receipt of a pro- 
mising UFO report scientists armed with a variety of obser- 
vational tools flew to the scene, in some cases to witness the 
phenomena themselves. 

The result has been a series of case histories that reads like 
a modern, real-life collection of Sherlock Holmes episodes. 
The cases range from the eerily perplexing to the preposterous- 
ly naive. The reader is given a taste of the scientific method, 
even though the cases are often such that they defy anything 
approaching deductive analysis. 

The reader can also exercise his own judgment by com- 
paring this report with efforts to dispute it. For example a 
book has been published by a former member of the University 
of Colorado project who was dismissed. He and his co-author 
argue that the project may have been organized — without the 
knowledge of most of its staff — as a cover to divert attention 
from the real nature of UFOs. 

He supports this conspiracy hypothesis with what he con- 
siders evidence that two members of a panel of top scientists 
convened by the government in 1953 to assess the UFO situa- 
tion refused to sign the resulting report. That report found 
there was no threat to the nation in the UFOs and urged that 
they be stripped of their "aura of mystery." The panel feared 
that an enemy could exploit the tendency of the public toward 
hysterical behavior through "clogging of channels of commu- 
nication by irrelevant reports." Real indications of hostile 
action would then be ignored. 

The chairman of the panel was Dr. H. P. Robertson of the 
California Institute of Technology. According to surviving 
members of the panel no one dissented from its findings, al- 
though the name of one member was deleted before the report 
was declassified in 1966. The time was one of sensitivity about 
involvement of the Central Intelligence Agency in activities 
beyond its intelligence-gathering role and all references to the 
CIA's role in the panel's work, as well as names of its em- 
ployees and others involved in intelligence work, were deleted. 

Apart from these deletions, this document (Appendix U), 
like all other aspects of this report, is uncensored. Some of the 
documents presented here, as well as many of the UFO 
episodes, are offered to the public for the first time. 

Despite the efforts of some UFO enthusiasts to discredit the 
report in advance, a panel of the nation's most eminent scien- 
tists, chosen by the prestigious National Academy of Sciences, 


Scientific Study of Unidentified Flying Objects 

has examined it, chapter by chapter, and given it "straight 
As," so to speak. 

This "grading" of the report was performed at the request 
of the Air Force, which foresaw charges of "whitewash" if — 
as it earnestly expected — the Colorado study echoed earlier 
findings that even the most mysterious UFOs have not been 
shown to be of exotic origin. 

Concurrence by the Academy, representing the nation's 
most distinguished scientists, would help divert such criticism. 
It was understood originally that the Academy panel would 
be asked merely to assess the working methods of the Colorado 
team, rather than to endorse its conclusions, but the panel 
went further than that. It expressed clear-cut agreement with 
the findings. 

"We are unanimous in the opinion," the panel said, "that 
this has been a very creditable effort to apply objectively the 
relevant techniques of science to the solution of the UFO 
problem. The report recognizes that there remain UFO sight- 
ings that are not easily explained. The report does suggest, 
however, so many reasonable and possible directions in which 
an explanation may eventually be found, that there seems to 
be no reason to attribute them to an extraterrestrial source 
without evidence that is much more convincing. The report 
also shows how difficult it is to apply scientific methods to the 
occasional transient sightings with any chance of success. 
While further study of particular aspects of the topic (e.g., 
atmospheric phenomena) may be useful, a study of UFOs in 
general is not a promising way to expand scientific understand- 
ing of the phenomena. On the basis of present knowledge the 
least likely explanation of UFOs is the hypothesis of extra- 
terrestrial visitations by intelligent beings." 

The Chairman of this panel was Dr. Gerald M. Clemence of 
Yale University, former Scientific Director of the United States 
Naval Observatory. The others included leading specialists in 
fields relevant to the UFO problem — astronomy, atmospheric 
physics, meteorology and psychology. They were: 

Dr. Horace R. Crane, Professor of Physics, University of 

Dr. David M. Dennison, Professor of Physics, University of 

Dr. Wallace O. Fenn, physiologist and former Director of 
the Space Science Center at the University of Rochester. 

Dr. H. Keffer Hartline, biophysicist, Professor at Rockefel- 
ler University and 1967 co-winner of the Nobel Prize in me- 
dicine and physiology. 

Dr. Ernest R. Hilgard, Professor of Psychology at Stanford 

Dr. Mark Kac, mathematician, Professor at Rockefeller 


Dr. Francis W. Reichelderfer, former head of the United 
States Weather Bureau. 

Dr. William W. Rubey, Professor of Geology and Geophy- 
sics at the University of California at Los Angeles. 

Dr. Charles D. Shane, Emeritus Astronomer at the Lick 
Observatory in California. 

Dr. Oswald G. Villard, Jr., Director of the Radio Science 
Laboratory, Stanford University. 

The panel did a certain amount of homework, in addition 
to reviewing the Colorado report. It read scientific papers 
prepared by outspoken scientific protagonists on both sides of 
the controversy. Two of these, Dr. William Markowitz, former 
head of the time service at the Naval Observatory, and Dr. 
Donald H. Menzel, former director of the Harvard College 
Observatory, have scoffed at the extraterrestrial hypothesis. 
Another author, Dr. James E. McDonald of the University of 
Arizona, has argued that UFOs are one of the biggest scientific 
puzzles of our time and that visitations from afar are the best 
explanation for UFOs that cannot otherwise be explained. 

In forwarding the panel's assessment to the Air Force Dr. 
Frederick Seitz, President of the Academy, said: "Substantial 
questions have been raised as to the adequacy of our research 
and investigation programs to explain or to determine the na- 
ture of these sometimes puzzling reports of observed pheno- 
mena. It is my hope that the Colorado report, together with 
our panel review, will be helpful to you and other responsible 
officials in determining the nature and scope of any continuing 
research effort in this area." 

The panel report was copyrighted to prevent its appearance 
in unauthorized publications. The review was done, Dr. Seitz 
said, "for the sole purpose of assisting the government in 
reaching a decision on its future course of action. Its use in 
whole or in part for any other purpose would be incompatible 
with the purpose of the review and the conditions under which 
it was conducted." 

Apparently the Academy and its panel members did not 
want their review to appear between the covers of some of 
the more far-out UFO books. However, the review was dis- 
tributed to the press on January 8, 1969, with the Colorado 
report itself, for release the next day. 

The report is a memorable document. While the case his- 
tories read like detective stories, it is also a scientific study. 
There are sections here and there that most readers will find 
technical and difficult to follow. They are easily skipped. 
However, in the technical sections there are also nuggets that 
no one will want to miss. For example in Chapter 7, on at- 
mospheric electricity and plasma interpretations of UFOs, 
there are accounts of collisions of Soviet and American air- 
craft with a peculiar phenomenon known as ball lightning, as 
well as a description of the extraordinary behavior of lightning 


Scientific Study of Unidentified Flying Objects 

inside a tornado. Also of special interest is the section de- 
scribing UFOs observed by astronauts (all presumably man- 
made objects in earth orbit). 

Efforts have been made by UFO enthusiasts to blunt the 
effect of this report by arguing that Dr. Condon and his col- 
leagues were too biased for a meaningful finding. These at- 
tempts to discredit the report have concentrated in large 
measure on an episode that occurred when much of the 
on-the-spot investigation had been done. 

Early in the project things seemed to be going smoothly. 
The two largest quasi-scientific organizations of UFO "buffs" 
cooperated by tipping off the Colorado project to new sight- 
ings. They also made available samples from their files of 
interviews, photographs and the like. 

Then, however, a certain amount of infighting developed. 
One of the UFO groups, NICAP, is headed by Donald Keyhoe 
who, as author of Flying Saucers Are Real, has a vested 
interest in the confirmation of his thesis. Various statements 
attributed to Dr. Condon suggested to NICAP that he did 
not take very seriously the possibility that UFOs come from 
another civilization. 

In this respect it should be pointed out that Dr. Condon 
is a somewhat garrulous soul who loves to spin a good yarn. 
The inquiry into UFOs was a rich source of such material and 
he found it hard, on various occasions, not to recount some 
of the sillier episodes. 

This infuriated those, like Dr. McDonald at the University 
of Arizona, who believed in the possibility of an extraterres- 
trial origin. They charged that the Colorado project was 
wasting its time on crackpot reports and turning its back on 
the more solid evidence. Anyone who reads the following 
pages will see that this is untrue. It is obvious that the project 
concentrated on the best documented and most substantial 
cases and it did not hesitate to conclude that, on the basis of 
available evidence, some are difficult to explain by conven- 
tional means. 

The most severe blow to the project came when one of its 
staff members, going through the files, came across a memo- 
randum written by Robert J. Low before the University under- 
took the project. Low, who was serving as project coordinator, 
had been an assistant dean in the graduate school. His memo, 
to University officials, sought to analyze the pros and cons of 
the Air Force proposal. Could the University undertake the 
project in a manner that would satisfy public concern, yet not 
subject the University to ridicule by the academic community? 
He argued that the study would perforce be done almost en- 
tirely by nonbelievers and, while the project could never 
"prove" that no UFOs have ever come from another world, 
it could contribute impressive evidence for such a conclusion. 
"The trick," he wrote, "would be, I think, to describe the 


project so that, to the public, it would appear a totally ob- 
jective study but, to the scientific community, would present 
the image of a group of nonbelievers trying their best to be 
objective, but having an almost zero expectation of finding 
a saucer." 

He proposed, to this end, that the emphasis be on the 
psychological and sociological investigation of those reporting 
UFOs, rather than on checking out the physical evidence for 
alleged visitations. 

Condon apparently never saw this memo at the time it was 
written and, in fact, rejected suggestions that the emphasis be 
on the psychology of UFO witnesses. As the case histories in 
this report show, the stress was on the search for physical 
evidence and physical explanations. However, the Low memo 
fell into the hands of Dr. McDonald and of NICAP. it was 
brought to the attention of John G. Fuller, author of two 
books (Incident at Exeter and Interrupted Journey) supporting 
the extraterrestrial explanation for UFOs. In an article in 
Look magazine, which had published parts of his two books, 
Fuller quoted the memo and reported dissension among staff 
members of the Colorado project. His article was entitled 
"Flying Saucer Fiasco," with the subtitle: "The Extraordinary 
Story of the Half-Million-Dollar 'Trick' to Make Americans 
Believe the Condon Committee Was Conducting an Objective 

Two men whom Condon considered responsible for leaking 
the memo to disgruntled UFO believers were discharged from 
the project. 

In exploring possible roots of this controversy the journal 
Science quoted a statement by James and Coral Lorenzen, 
who run the Aerial Phenomena Research Organization 
(APRO) in Tucson, Arizona, which rivals NICAP as a 
comparatively sober association of UFO buffs. They sug- 
gested that there was "a strong attempt by the NICAP group 
(McDonald and Saunders are both close to NICAP) to con- 
trol the study. When they found they couldn't control it, they 
attempted to scuttle it." 

Whatever the merits of this analysis, the Condon Report 
and the challenges to it must stand or fall on their own merits 
— not on the degree of squabbling that may, or may not have 
occurred in its preparation. That Condon, an old scientific 
pro, was well aware of this shines forth from the pages of 
this document. 

There is probably no such thing as a scientific researcher 
without bias. It is rare indeed for someone to undertake an 
experiment with no inkling as to its outcome. More commonly 
the scientist has formulated a hypothesis and he carries out a 
series of experiments that, he hopes, will convince himself — 
and all the world — of its correctness. Those experiments, to 
assure him of a place in scientific history, must, insofar as 


Scientific Study of Unidentified Flying Objects 

possible, be such that any other scientist can confirm his 

The extent to which such tests can be applied to UFOs is 
limited. More often, as the case histories show, the judgement 
must be based on common sense. If, for example, it can be 
shown that a UFO photograph could have been faked, and if 
the story told by the person who took the picture displays 
suspicious inconsistencies, then Condon and his colleagues 
have tended to reject the picture as evidence. Those inclined 
to be believers might be more willing to accept the picture as 
genuine, but they could not use it as "proof" of the extra- 
terrestrial hypothesis. 

A reading of the case histories in this report forces on the 
reader a certain humility regarding human perception. We 
do not see only with our eyes and hear only with our ears. 
We see and hear with that complex and little-understood 
organ, the brain, crammed with memories and earlier 

It is the ingenuity of this brain that enables us to read fast 
or recognize a friend at a glance. If we had to read every letter 
of every word, or had to scrutinize the entire physiognomy of 
a person to recognize him, the pace of our lives would be slow 
indeed. Instead we have learned to deduce entire words or 
phrases and entire people from a limited number of observed 

However, when the circumstances are unusual we can 
easily be fooled by misleading clues. Nicolaas Tinbergen, 
Professor of Animal Behavior at Oxford and a founder of 
the young science of ethology (the study of animal behavior 
in the wild), told me of a personal experience that illustrates 

In east Greenland he was once atop a mountain a number 
of miles inland. Offshore wind had blown the pack ice beyond 
the horizon some days earlier and now, to his horror, he saw 
the distant sea in violent motion. Giant waves were racing 
toward shore. "We must get down off the mountain," he told 
his Eskimo companion excitedly. "That gale could hit any 
minute and blow us off the mountain!" 

Then suddenly the motion of the sea stopped as though a 
moving picture had been brought to a halt. This occurred at 
the moment when his mind realized that he was looking at 
pack ice that had blown back onshore, not at waves. The 
motion was a fiction of his brain. 

It was not many generations ago that ghosts seemed plaus- 
ible, and night visions, be they wisps of luminous gas rising 
from a swamp, or play of moonlight on a blowing curtain, 
could raise palpitations in the most stalwart heart. Today, if 
one hears a creak in the night or sees a peculiar glow, the 
usual reaction is to investigate, rather than duck under the 


covers. However, UFOs are often too far away for such 
intimate checking. 

This report, in showing the fallibility of even such sober 
observers as policemen, airline pilots and radar operators, 
raises questions as to the role of conditioning in many other 
fields of human activity. The purveyors of advertising are well 
versed in the techniques of conditioning, but one wonders to 
what extent this phenomenon affects such basic attitudes as 
our nationalism, our theological point of view and our moral 

Are they really founded on logic and the ultimate truth? 

One cannot help but view our points of view on a great 
many things with new skepticism. 

Anyone who reads this study will, I believe, lay it down 
with a new perspective on human values and limitations. 

Walter Sullivan 


Scientific Study of Unidentified Flying Objects 

Section I 

Edward U. Condon 

We believe that the existing record and the results, of the 
Scientific Study of Unidentified Flying Objects of the Univer- 
sity of Colorado, which are presented in detail in subsequent 
sections of this report, support the conclusions and recom- 
mendations which follow. 

As indicated by its title, the emphasis of this study has been 
on attempting to learn from UFO reports anything that could 
be considered as adding to scientific knowledge. Our general 
conclusion is that nothing has come from the study of UFOs 
in the past 21 years that has added to scientific knowledge. 
Careful consideration of the record as it is available to us 
leads us to conclude that further extensive study of UFOs 
probably cannot be justified in the expectation that science will 
be advanced thereby. 

It has been argued that this lack of contribution to science is 
due to the fact that very little scientific effort has been put on 
the subject. We do not agree. We feel that the reason that there 
has been very little scientific study of the subject is that those 
scientists who are most directiy concerned, astronomers, at- 
mospheric physicists, chemists, and psychologists, having had 
ample opportunity to look into the matter, have individually 
decided that UFO phenomena do not offer a fruitful field in 
which to look for major scientific discoveries. 

This conclusion is so important, and the public seems in gen- 
eral to have so little understanding of how scientists work, 
that some more comment on it seems desirable. Each person 
who sets out to make a career of scientific research, chooses a 
general field of broad specialization in which to acquire pro- 
ficiency. Within that field he looks for specific fields in which 
to work. To do this he keeps abreast of the published scientific 
literature, attends scientific meetings, where reports on current 
progress are given, and energetically discusses his interests and 
those of his colleagues both face-to-face and by correspond- 
ence with them. He is motivated by an active curiosity about 
nature and by a personal desire to make a contribution to sci- 
ence. He is constantly probing for error and incompleteness 
in the efforts that have been made in his fields of interest, and 


looking for new ideas about new ways to attack new problems. 
From this effort he arrives at personal decisions as to where 
his own effort can be most fruitful. These decisions are per- 
sonal in the sense that he must estimate his own intellectual 
limitations, and the limitations inherent in the working situa- 
tion in which he finds himself, including limits on the support 
of his work, or his involvement with other pre-existing scien- 
tific commitments. While individual errors of judgment may 
arise, it is generally not true that all of the scientists who are 
actively cultivating a given field of science are wrong for very 

Even conceding that the entire body of "official" science 
might be in error for a time, we believe that there is no better 
way to correct error than to give free reign to the ideas of 
individual scientists to make decisions as to the directions in 
which scientific progress is most likely to be made. For legal 
work sensible people seek an attorney, and for medical treat- 
ment sensible people seek a qualified physician. The nation's 
surest guarantee of scientific excellence is to leave the decision- 
making process to the individual and collective judgment of 
its scientists. 

Scientists are no respecters of authority. Our conclusion that 
study of UFO reports is not likely to advance science will not 
be uncritically accepted by them. Nor should it be, nor do we 
wish it to be. For scientists, it is our hope that the detailed 
analytical presentation of what we were able to do, and of what 
we were unable to do, will assist them in deciding whether or 
not they agree with our conclusions. Our hope is that the de- 
tails of this report will help other scientists in seeing what the 
problems are and the difficulties of coping with them. 

If they agree with our conclusions, they will turn their valu- 
able attention and talents elsewhere. If they disagree it will be 
because our report has helped them reach a clear picture of 
wherein existing studies are faulty or incomplete and thereby 
will have stimulated ideas for more accurate studies. If they 
do get such ideas and can formulate them clearly, we have no 
doubt that support will be forthcoming to carry on with such 
clearly-defined, specific studies. We think that such ideas for 
work should be supported. 

Some readers may think that we have now wandered into 
a contradiction. Earlier we said that we do not think study of 
UFO reports is likely to be a fruitful direction of scientific 
advance; now we have just said that persons with good ideas 
for specific studies in this field should be supported. This is no 
contradiction. Although we conclude after nearly two years 
of intensive study, that we do not see any fruitful lines of 
advance from the study of UFO reports, we believe that any 
scientist with adequate training and credentials who does come 
up with a clearly defined, specific proposal for study should 
be supported. 


Scientific Study of Unidentified Flying Objects 

What we are saying here was said in a more general context 
nearly a century ago by William Kingdon Clifford, a great 
English mathematical physicist. In his "Aims and Instruments 
of Scientific Thought" he expressed himself this way: 

Remember, then, that [scientific thought] is the guide of 
action; that the truth which it arrives at is not that which we 
can ideally contemplate without error, but that which we may 
act upon without fear; and you cannot fail to see that scien- 
tific thought is not an accompaniment or condition of human 
progress, but human progress itself. 

Just as individual scientists may make errors of judgment 
about fruitful directions for scientific effort, so also any indi- 
vidual administrator or committee which is charged with de- 
ciding on financial support for research proposals may also 
make an error of judgment. This possibility is minimized by 
the existence of parallel channels, for consideration by more 
than one group, of proposals for research projects. In the 
period since 1945, the federal government has evolved flexible 
and effective machinery for giving careful consideration to 
proposals from properly qualified scientists. What to some 
may seem like duplicated machinery actually acts as a safe- 
guard against errors being made by some single official body. 
Even so, some errors could be made but the hazard is reduced 
nearly to zero. 

Therefore we think that all of the agencies of the federal 
government, and the private foundations as well, ought to be 
willing to consider UFO research proposals along with the 
others submitted to them on an open-minded, unprejudiced 
basis. While we do not think at present that anything worth- 
while is likely to come of such research each individual case 
ought to be carefully considered on its own merits. 

This formulation carries with it the corollary that we do 
not think that at this time the federal government ought to set 
up a major new agency, as some have suggested, for the 
scientific study of UFOs. This conclusion may not be true for 
all time. If, by the progress of research based on new ideas in 
this field, it then appears worthwhile to create such an agency, 
the decision to do so may be taken at that time. 

We find that there are important areas of atmospheric optics, 
including radio wave propagation, and of atmospheric elec- 
tricity in which present knowledge is quite incomplete. These 
topics came to our attention in connection with the interpre- 
tation of some UFO reports, but they are also of fundamental 
scientific interest, and they are relevant to practical problems 
related to the improvement of safety of military and civilian 

Research efforts are being carried out in these areas by the 
Department of Defense, the Environmental Science Services 
Administration, the National Aeronautics and Space Admin- 


istration, and by universities and nonprofit research organiza- 
tions such as the National Center for Atmospheric Research, 
whose work is sponsored by the National Science Foundation. 
We commend these efforts. By no means should our lack of 
enthusiasm for study of UFO reports as such be misconstrued 
as a recommendation that these important related fields of sci- 
entific work not be adequately supported in the future. In an 
era of major development of air travel, of space exploration, 
and of military aerospace activities, everything possible should 
be done to improve our basic understanding of all atmospheric 
phenomena, and to improve the training of astronauts and air- 
craft pilots in the recognition and understanding of such 

As the reader of this report will readily judge, we have 
focussed attention almost entirely on the physical sciences. 
This was in part a matter of determining priorities and in 
part because we found rather less than some persons may have 
expected in the way of psychiatric problems related to belief 
in the reality of UFOs as craft from remote galactic or inter- 
galactic civilizations. We believe that the rigorous study of the 
beliefs — unsupported by valid evidence — held by individuals 
and even by some groups might prove of scientific value to 
the social and behavioral sciences. There is no implication here 
that individual or group psychopathology is a principal area of 
study. Reports of UFOs offer interesting challenges to the stu- 
dent of cognitive processes as they are affected by individual 
and social variables. By this connection, we conclude that a 
content-analysis of press and television coverage of UFO re- 
ports might yield data of value both to the social scientist and 
the communications specialist. The lack of such a study in 
the present report is due to a judgment on our part that other 
areas of investigation were of much higher priority. We do not 
suggest, however, that the UFO phenomenon is, by its nature, 
more amenable to study in these disciplines than in the physi- 
cal sciences. On the contrary, we conclude that the same 
specificity in proposed research in these areas is as desirable 
as it is in the physical sciences. 

The question remains as to what, if anything, the federal 
government should do about the UFO reports it receives from 
the general public. We are inclined to think that nothing should 
be done with them in the expectation that they are going to 
contribute to the advance of science. 

This question is inseparable from the question of the na- 
tional defense interest of these reports. The history of the past 
21 years has repeatedly led Air Force officers to the conclusion 
that none of the things seen, or thought to have been seen, 
which pass by the name of UFO reports, constituted any haz- 
ard or threat to national security. 

We felt that it was out of our province to attempt an inde- 
pendent evaluation of this conclusion. We adopted the attitude 


Scientific Study of Unidentified Flying Objects 

that, without attempting to assume the defense responsibility 
which is that of the Air Force, if we came across any evidence 
whatever that seemed to us to indicate a defense hazard we 
would call it to the attention of the Air Force at once. We did 
not find any such evidence. We know of no reason to question 
the finding of the Air Force that the whole class of UFO 
reports so far considered does not pose a defense problem. 

At the same time, however, the basis for reaching an opinion 
of this kind is that such reports have been given attention, one 
by one, as they are received. Had no attention whatever been 
given to any of them, we would not be in a position to feel 
confident of this conclusion. Therefore it seems that only so 
much attention to the subject should be given as the Depart- 
ment of Defense deems to be necessary strictly from a defense 
point of view. The level of effort should not be raised because 
of arguments that the subject has scientific importance, so far 
as present indications go. 

It is our impression that the defense function could be per- 
formed within the framework established for intelligence and 
surveillance operations without the continuance of a special 
unit such as Project Blue Book, but this is a question for de- 
fense specialists rather than research scientists. 

It has been contended that the subject has been shrouded in 
official secrecy. We conclude otherwise. We have no evidence 
of secrecy concerning UFO reports. What has been miscalled 
secrecy has been no more than an intelligent policy of delay in 
releasing data so that the public does not become confused by 
premature publication of incomplete studies of reports. 

The subject of UFOs has been widely misrepresented to the 
public by a small number of individuals who have given sensa- 
tionalized presentations in writings and public lectures. So far 
as we can judge, not many people have been misled by such 
irresponsible behavior, but whatever effect there has been has 
been bad. 

A related problem to which we wish to direct public atten- 
tion is the miseducation in our schools which arises from the 
fact that many children are being allowed, if not actively en- 
couraged, to devote their science study time to the reading of 
UFO books and magazine articles of the type referred to in the 
preceding paragraph. We feel that children are educationally 
harmed by absorbing unsound and erroneous material as if it 
were scientifically well founded. Such study is harmful not 
merely because of the erroneous nature of the material itself, 
but also because such study retards the development of a 
critical faculty with regard to scientific evidence, which to some 
degree ought to be part of the education of every American. 

Therefore we strongly recommend that teachers refrain from 
giving students credit for school work based on their reading 
of the presently available UFO books and magazine articles. 
Teachers who find their students strongly motivated in this 


direction should attempt to channel their interests in the direc- 
tion of serious study of astronomy and meteorology, and in the 
direction of critical analysis of arguments for fantastic propo- 
sitions that are being supported by appeals to fallacious reason- 
ing or false data. 

We hope that the results of our study will prove useful to 
scientists and those responsible for the formation of public 
policy generally in dealing with this problem which has now 
been with us for 21 years. 


A noted woman astronomer discusses current knowledge, 
and lack of knowledge, concerning the evolution of 
galaxies. Dr. Burbidge concludes "It is difficult to 
understand in detail how one sort of galaxy can evolve 
into another, yet in a general way we know that it 
must happen. " 

22 The Life-Story of a Galaxy 

Margaret Burbidge 

An excerpt from Stars and Galaxies: Birth, Aging and Death in the Universe, 1962. 

A fairly coherent picture has been built up of the evolu- 
tion and life-history of single stars; can we make such a co- 
herent picture of the evolution or life-history of a galaxy? At 
the moment our success is not as clear-cut as in the case of the 
life-history of a star. For example, you have seen in Chapter 
VI that there can be opposite points of view about the radio 
stars; in one interpretation two galaxies are colliding; in the 
other, a single galaxy is splitting into two parts. At the moment, 
we have no physical theory or explanation which could fit this 
second suggestion. In fact, the whole problem of the probable 
course of evolution of a galaxy is more difficult and complex 
than for a star. This is not to say that we shall not solve it in 
the comparatively near future; after all, the evolution of stars 
was only poorly understood ten years ago. Since then most of 
the story (Chapters III and IV) has been put together, and who 
knows what the next ten years will bring to our understanding 
of the evolution of galaxies. 

Chapter V describes the different kinds of galaxies that we 
see in the sky: spiral galaxies, irregular galaxies without much 
structure to them, and the smooth ones that we call elliptical 
galaxies. All these different kinds of galaxies are made up of 
three components — gas, dust, and stars. There is more gas and 
dust in irregulars and spirals than in the ellipticals, which have 
almost none. In trying to trace out the life-history of a galaxy, 
one way to begin is to look for a time sequence between these 
different kinds of galaxies. Might one kind of galaxy change 
into another? If so, which are younger? Which are older? 


From Gas to Galaxy 

In Chapter V two alternative cosmological theories were 
described. According to the "Big-Bang" Theory the universe 
was created at some definite time in the past; matter was then 
very much closer together in space. Somewhat later all the 
galaxies might have been formed at one time. By contrast, ac- 
cording to the "Steady-State" Theory, the universe has been 
about the same all along, and galaxies must be forming now. In 
either case it is likely that the material out of which the galaxies 
formed was originally all gas, containing no stars or dust, and 
spread more or less uniformly throughout space. If a gas is uni- 
formly spread through space, it tends to "clot." If any little 
fluctuation takes place, one region by chance becoming a bit 
more dense than another, then the denser region tends to grow, 
attracting to itself more material by gravitational force. The 
clots would grow and might easily turn into galaxies. 

On this basis, we shall sketch in quite general fashion what 
might be the life-history of a galaxy — not what can be proved, 
but what would be reasonable. Starting, then, with a gas spread 
uniformly throughout all space, fluctuations begin to form 
what we will call "proto-galaxies." At some stage there will be 
smaller fluctuations inside a proto-galaxy, and out of these 
smaller fluctuations stars could form. We will call these "first- 
generation stars" — the first stars to form in a galaxy — and the 
gas they formed from might have been pure hydrogen, according 
to the view that the chemical elements have been built up in 
the stars, as discussed in Chapter IV. The "Steady-State" 
Theory, of course, suggests that the gas was not pure hydrogen 
but had a slight mixture of heavier elements ejected from 
earlier generations of stars and galaxies that had always been 
around in space. 

In either case, the gas that formed the first generation of stars 
in a new galaxy would have very little of the heavier elements. 

The Life-Story of a Galaxy 

It would be mostly hydrogen. From the early stages of a star's 
life discussed in Chapter IV, we know that the more massive a 
blob of matter that starts condensing, the faster it will contract 
under its own gravitation to form a star. During contraction, the 
gas becomes quite hot because of the release of gravitational en- 
ergy as the gas falls in toward the center. Just as gravitational 
energy is released in the condensation of a star, so gravitational 
energy will be released in the formation of a galaxy; therefore 
the gas at an early stage in the proto-galaxy might be quite hot. 

The Youth of a Galaxy 

Because the large, hot, blue stars form rapidly, they will 
generally be imbedded in thinner gas that has not yet condensed 
into stars. The radiation from these hot stars would cause the 
gas they are imbedded in to shine quite brightly. Patches of 
glowing gas like this will show up very well in a galaxy and are 
seen in many irregular and spiral galaxies. This is the sort of 
situation we would expect in a young galaxy, and one that we see 
in the irregular galaxies shown in Figures V-2 and VII-i. There 
is no pattern; an irregular galaxy is just an unorganized collec- 
tion of blobs of hot gas shining because they are lit up by mas- 
sive blue stars imbedded in them. So we might think that an 
irregular galaxy would be quite young, though there are possi- 
ble pitfalls in this suggestion, as noted later on. 

What would happen next in a young galaxy after the first 
generation of large, hot stars has formed? These first, massive 
stars will go through their life-histories fairly quickly, in the 
manner described in Chapter III, using up all their nuclear 
fuel. Ten or twenty million years later, at the end of their lives, 
they should turn into white dwarfs, but they are each so massive 
that the whole star cannot shrink to a white dwarf without 
losing a large part of its mass. So these first-generation stars 


Figure VII-i. An irregular galaxy, NGC 4449. Such an unorganized 
collection of blue giant stars and blobs of glowing gas is generally 
considered young in age, since the blue giant stars are expected to 
be short lived. Mount Wilson and Palomar Observatories 


The Life-Story of a Galaxy 

Figure V-2. The Large Magellanic Cloud, an irregular galaxy. This 
is one of two such clouds easily visible in the southern hemisphere, 
but never above the horizon for us in the United States. These two 
clouds of Magellan are the nearest known galaxies outside our own. 

Mount Wilson and Palomar Observatories 


would have to put back into the interstellar material of the 
galaxy a good deal of the material of which they were made. 
And this material will have become enriched in the chemical 
elements "cooked up" in the interiors of the stars: elements 
such as helium, carbon, nitrogen, and iron. 

Some of these heavier elements, once they get out into the 
space between the stars, can stick together and form dust grains, 
which pure hydrogen cannot do. (Two hydrogen atoms can 
stick together in a hydrogen molecule, but these molecules will 
not form solid dust particles.) And, once the oxygen, carbon, 
nitrogen, and so on, make dust grains, the gas, now with a mix- 
ture of dust in it, can cool. We saw that, in the early history of 
a galaxy, the gas would be hot; once some dust has formed, the 
gas can cool because the dust helps the gas to radiate away its 
heat energy. As the gas in a galaxy becomes cool, the pressure 
drops and it can fall together — condense under its own gravita- 
tional attraction — much more easily and rapidly. Thus it is 
much easier to form the second and later generations of stars 
from small density fluctuations. 

Order Produced by Rotation 

In Chapter V, it was shown that galaxies rotate about 
their axes. What would happen to an irregular galaxy if it 
rotates? Could it remain irregular? Star formation is going on, 
gas is contracting under its own gravitation, and the whole as- 
semblage is rotating as well. We can expect a symmetrical and 
orderly structure to be produced from this formless mass of 
material just as a shapely vase can be made of formless clay. It 
is difficult to make a symmetrical object out of a lump of clay 
unless you have a potter's wheel to rotate the clay; then it is 
quite easy. So, we can understand how a galaxy could become 
more symmetrical-looking from its rotation. An irregular galaxy 
that started out with relatively few massive blue stars, and no 


The Life-Story of a Galaxy 

pattern whatever in its structure, would gradually begin to take 
on a regular, symmetrical shape, with more of the mass collected 
at the center, and a generally circular outline. The cooling of 
the gas left over after the stars form would help this gas to 
contract toward the central or equatorial plane of the galaxy, 
and soon all of the gas and dust would lie in a thin layer or 
sheet in the central plane, as described in Chapter VI. 

While this was happening — while the new galaxy was shrink- 
ing and speeding up its rotation, forming a more regular pat- 
tern — star formation would be going on continuously. As each 
generation of stars forms, the brightest members (which would 
be the most massive, high-temperature stars) will evolve and go 
through their lives most rapidly, come to the end stage, and 
return most of their substance to the space between the stars. 
But each generation will also contain some stars with a small 
mass. These small-mass stars, stars like our sun or smaller, with 
very long lifetimes, will not complete the full cycle that the hot 
bright stars go through — the cycle from dust to dust and gas to 
gas. Therefore, there should be a gradual using-up of the ma- 
terial of the galaxy; matter would gradually become locked up 
in low-mass stars whose lifetimes are so long that they take little 
part in the interchange between interstellar gas and stars. 

Signs of a Galaxy's Age 

There are also the stellar remains — skeletons, if you like 
— the white dwarfs left over after the massive stars have gone 
through their life cycle. An increasing fraction of the material 
of the galaxy will gradually get locked up in the form of white 
dwarfs; and that fraction can take no further part in the inter- 
change between interstellar gas and stars. Thus, the gas in a 
galaxy will gradually get used up, until eventually there will 
be none left to form any new stars; in such an aged galaxy we 


expect only fairly cool stars of small mass, a few red giants 
into which such stars evolve, and some white dwarfs. 

All this suggests that there are indicators of the evolutionary 
age of a galaxy — things which could be observed and measured 
from a large distance. We need features that can be measured 
from great distances if we are to get information about a large 
part of the universe, and about conditions billions of years ago — 
for we see the distant galaxies as they were then. We could 
measure, in the first place, the color of a galaxy. In Chapter II 
we saw how the colors of stars can be measured; the colors of 
galaxies, which are whole collections of stars, can be measured 
in the same way. If a galaxy has a red color it is likely to be 
made up mostly of old stars all of which have a reddish color — 
stars of a smaller mass than the sun and the red giant stars into 
which they would evolve. On the other hand, a young, irregular 
galaxy would have a bluer color because it is largely made up 
of hot, blue stars. Color thus would be an indicator of the 
evolutionary age of a galaxy. 

We can also measure the spectrum of a galaxy, made up of 
the spectra of all the stars in it — an average or composite spec- 
trum that might reveal the kinds of stars that make up a galaxy. 

Another thing to measure is the mass of a galaxy, determined 
by studying how fast it is rotating (Chapter V). Having meas- 
ured the mass of a galaxy, and the total light it puts out, we can 
determine the ratio: the mass divided by the luminosity. If we 
do this for a single star — the sun, for example — we get a certain 
value of tons mass per billion kilowatts of radiation. For a star 
cooler than the sun we find that the mass divided by the light is 
a larger number because of the way in which the luminosity 
depends so strongly on mass (Chapters III and IV). Stars of low 
mass put out relatively very little light, whereas stars of high 
mass are much more spendthrift of their energy. Hence the 
mass of a galaxy divided by its luminosity is a fairly good indica- 
tion of the average kind of stars in that galaxy. Of course, it 


The Life-Story of a Galaxy 

would be better if we could actually study the individual stars, 
but unfortunately galaxies are so far away that we can only 
study the brightest individual stars in a few of the nearest ones. 
What we need is a great deal of information about a very large 
number of galaxies. 

A galaxy that we might think of as being at a somewhat later 
stage in its life history is shown in Figure I-io. This spiral 
galaxy still has many bright patches in it which we find to be 
patches of hot gas lit by bright stars. These are spread all 
through it, just as they are spread through an irregular galaxy. 
But this spiral has a clearly defined center, a fairly circular out- 
line, and characteristic spiral arms. The color of a spiral like 
this is a little redder than an irregular galaxy, and from its 
composite spectrum it seems to have a higher proportion of 
yellow stars like the sun than does an irregular galaxy. All of 
this indicates that a loose spiral galaxy is at a later stage in its 
life-history than an irregular one. Figure V-i shows a tighter 
spiral galaxy (M31) where things have settled down and become 
still more orderly. M31 looks quite tidy; it has a nice bright 
little center, then a smooth region, and then the spiral arms 
neatly wound. Even in a galaxy like M31 there are many patches 
of gas not yet condensed into stars, which are lit up by nearby 
hot stars. 

Factors that May Influence the Evolution of Galaxies 

Finally, the elliptical galaxies in Figure V-4 are quite 
smooth. They are much brighter in the center than in their 
outer parts but they have no bright patches of gas, and seem to 
be made up entirely of stars. All the gas has been used up. 
Elliptical galaxies have the reddest color of all, and their com- 
posite spectra show that their stars are, on the average, low-mass 
stars like the sun and the red giants into which such stars evolve. 


What about the ratio of mass to luminosity? Unfortunately, we 
do not have much information yet on the masses of elliptical 
galaxies, but the average for a few shows that they have a much 
higher ratio of mass to luminosity than the spiral and irregular 
galaxies. This again suggests that they are at a later stage in their 

Can we now say that an irregular galaxy will turn into a 
spiral galaxy and, when all the gas is used up, the spiral will 
turn into an elliptical galaxy? Can we say that we have an 
evolutionary sequence, irregular types evolving into spirals, and 
spirals evolving into ellipticals? Harlow Shapley, the famous 
Harvard astronomer, first suggested about a decade ago that 
this was happening. But we must keep in mind the warning 
example set by studies of the evolution of stars. We know that 
there are many different kinds of stars in the sky, but that we 
cannot put all these stars into one evolutionary sequence; we 

have seen in Chapter IV that the life-histories of stars of differ- 
ent masses are very different. In fact, if we want to make sense 
of the life-history of stars, we have to sort the stars first into 
groups with the same age but different masses. We cannot say 
that a high-temperature, massive star will evolve into a star like 
the sun. But in this first attempt at the life-history of a galaxy 
we are trying to arrange all the different kinds of galaxies in a 
single evolutionary sequence. Perhaps this is not right — per- 
haps the mass of a galaxy plays an important role in determining 
its life-history, just as the mass of a star is very important in its 

Although we know the masses of only a few galaxies as yet, it 
does seem that irregular galaxies and spiral galaxies are, on the 
average, less massive than elliptical galaxies. How, then, could 
an irregular galaxy become a spiral galaxy and then an elliptical 
galaxy, with an increase in mass? 

There is further evidence from the double galaxies — galaxy 
twins, so to speak. For instance, the irregular galaxy M82 lies 


The Life-Story of a Galaxy 

Figure V-i. The Andromeda Galaxy, Messier 3/, a spiral galaxy. 
This largest and brightest of the nearby galaxies dwarfs its two com- 
panions, M32 on the left and NGC 205 on the right, in this photo- 
graph taken with the 48-inch Schmidt telescope. M31 is estimated to 
be over 2 million light-years from us. It is the nearest spiral 
galaxy, and can just be seen with the naked eye on a clear, dark 
night Mount Wilson and Palomar Observatories 


EO NGC 3379 

E2 NGC 221 (M32) 

E5 NGC 4621 (M59) 

E7 NGC 3115 

NGC 3034 (M82) 

NGC 4449 


The Life-Story of a Galaxy 

quite close in space to the large spiral galaxy, M81, and may 
have been formed out of the same general patch of material. It 
ought to have the same age, just as the stars in any one cluster 
are likely to have the same age. Is the irregular galaxy M82 the 
same age as the spiral galaxy M81 near it? M82 is probably a 
little less massive than the spiral galaxy M81, but it is rotating, 
and before very long it should surely settle down to a spiral 
structure. Why is M82 still an irregular galaxy? What stopped 
it from becoming a spiral galaxy like M81? 

There must be other factors, then, that determine the way in 
which a galaxy evolves, beside the mass it had to start with. The 
magnetic field is a possible factor, since magnetic fields are 
needed (Chapter VI) to explain those galaxies that are radio 
sources, and it is quite likely that there are magnetic fields in 
all galaxies, including our own. These magnetic fields are quite 
small in comparison to the magnetic field on the surface of the 
earth that causes a compass needle to point north. The magnetic 
field in our galaxy is only a few hundred-thousandths of this. 
Nevertheless, a magnetic field of this strength spread out 
through a whole galaxy involves a great deal of energy. 

If magnetic fields are stronger in some galaxies than in 
others, this might have an effect upon the speed at which in- 
terstellar gas could form into stars. A strong magnetic field could 
delay star formation because magnetic fields tend to "freeze" a 
conducting gas, making it behave more like a solid, and would 
tend to keep apart a blob of gas that was about to contract under 
its own gravitation into a star. In this way the magnetic fields in 
a galaxy may be important in determining its life-history. 

Another factor that might be important is the original density 
of the gas that contracted to form a galaxy. Suppose gas is con- 
tracting, and that, before it has achieved high average density, 
some fluctuations initiate star formation. This might lead to a 
slower over-all rate of formation than if all the gas forming a 
galaxy collapsed at once, reaching high density throughout be- 
fore the first generation of stars formed. 


The Origin of S-Zero (So) Galaxies 

Another objection to the idea that a spiral galaxy may 
turn into an elliptical one is connected with rotation. Looking 
at a spiral galaxy edge-on as in Figure I-u, we see how flat it 
is. Elliptical galaxies are never that flat. Once a galaxy has 
become extremely flat, it is difficult to see how it can round out 
again, as would be necessary if a spiral galaxy were to evolve 
into an elliptical galaxy. However, there is a kind of galaxy that 
has no spiral arms and yet is more flattened than the elliptical 
galaxies, and these are called So galaxies (see Chapter V). There 
are many galaxies of this sort in some of the giant clusters of 
galaxies, and it has been suggested that they were formed by 
chance collisions. In such a collision the stars of each galaxy just 
pass each other, simply because there is so much empty space 
between them. But the interstellar gas and dust clouds in the 
two galaxies will collide, and be separated from the stars. So col- 
lisions will sweep the gas out of spirals. S-zero galaxies, which 
are flat but have no interstellar clouds, might therefore be either 
the results of collisions between spiral galaxies, or simply aged 
spiral galaxies that have used up their gas and dust in forming 

Figure V1I-2 shows an So galaxy in which a small amount of 
gas remains. You can see that there is a very thin line of dust 
through the center, the region where the spiral arms used to be. 
The gas that makes spiral arms is mostly gone, leaving just stars 
and the remnants of stars. 

Winding Up of Spiral Arms 

Let us now consider the spiral arms in galaxies. They are 
fairly symmetrical, and this has a bearing on how they might be 
"wound up." The central region of a galaxy rotates faster than 


The Life-Story of a Galaxy 

Figure l-u. Spiral galaxy in Coma Berenices, NGC 4565. This 
galaxy is seen in edge-on view by chance. Compare it with Figure I-p 
to see why the stars of the Milky Way are considered to form a simi- 
lar object — a galaxy. Mount Wilson and Palomar Observatories 


the outer regions. An early idea about the formation of spiral 
arms, known as the "coffee-cup" theory, was based on the 
analogy of a cup of coffee stirred near the middle of the cup. 
The central part of the coffee goes around faster than the outer 
parts, and at the rim of the cup the coffee is not moving at all. A 
little thick cream poured in makes beautiful spiral arms, and it 
does not matter what shape the blobs of cream start with; the 
different speeds of rotation will spin them out into spiral shapes. 

It is easy, then, to understand how spiral arms are formed by 
the different rates of rotation in a galaxy; the difficulty is just 
the opposite: why don't all galaxies have much more extended 
spiral arms? If the galaxies are very old they must have rotated a 
great many times; an average galaxy will rotate, about halfway 
out from its center, once in perhaps a hundred million years, 
and will turn a large number of times in its full life (estimated 
to be ten billion years). We would expect to see spiral arms 
completely wound up in hundreds of turns, whereas the actual 
spiral galaxies (Figures I-io, V-i, V-3) usually have arms making 
just one or two turns. It seems that there must be some process 
that renews or preserves short spiral arms; otherwise the ob- 
served rotations of galaxies would wind them out of existence. 
Here again, it is tempting to assume that magnetic fields stiffen 
the material of a galaxy and prevent a spiral arm from winding 
up too far. They may also play some part in the formation or 
renewing of spiral arms. 

In addition to the ordinary spiral galaxies, as noted in 
Chapter V, there is the class of "barred spirals" — galaxies that 
have a bar across the center and two spiral arms starting from 
the ends of the bar {Figure V-3). The bar in such a galaxy rotates 
more or less like a solid wheel, but just beyond the end of the 
bar the material rotates more slowly so that the arms get trailed 
out. Something must "freeze" the straight bar into a rigid form 
so that it does not wind up into spiral arms. But Figure VII-} 
shows a different sort of barred spiral. It has a bar and two 


The Life-Story of a Galaxy 

Figure VII-2. An So galaxy, NGC 3866. The S-zero (So) type of 
galaxy is flat like a spiral but shows no spiral arms and is often 
called a transition stage between spiral and elliptical types. This one 
has a thin line of dust in it, as a depleted spiral might. 

Mount Wilson and Palomar Observatories 


large spiral arms, but in the very center there is another little 
spiral, which turns out to be rotating very fast. It is hard to see 
how the bar could last very long without getting wound up in 
the central spiral. There are several other barred spirals like 
this, and there is a great deal to be learned before we can hope 
to understand them. 

Are Galaxies Forming Now? 

Finally, do we see any galaxies that we think are really 
young — actually young in years? The "Steady-State" cosmologi- 
cal theory predicts that we should see some galaxies formed very 
recently; the "Big-Bang" Theory, although it does not say that 
there could be no young galaxies, must explain them in some 
special way. Figure VII-4 shows one of the few galaxies we can 
claim are fairly young. It is a very odd thing — an ordinary 
elliptical galaxy accompanied by nearby patches of gas that 
must have bright, hot stars in them. A galaxy like this could 
not last very long in its present stage; perhaps this elliptical 
galaxy, moving through space, captured some left-over material 
— a blob of gas in which no stars had formed. As a result of the 
capture, this blob of gas could contract a little, until it was 
dense enough in some places for stars to form. That is, a young 
galaxy was formed in the presence of an old one. 

Figure VII-5 shows two galaxies rather far away from us and 
located in one of the big clusters of galaxies, the Coma cluster. 
A long tail sticks out of the upper galaxy, and another tail from 
the lower one. You would think such tails must wind up; a tail 
cannot remain just sticking out into space from a galaxy if that 
galaxy is rotating at all. And these galaxies are rotating rapidly, 
as measured by Doppler shifts in their spectra (see Chapter II). 
That is, a straight, protruding tail makes it very likely that 
such a galaxy is very young. 


The Life-Story of a Galaxy 

Figure I-io. An open spiral galaxy in Eridanus, NGC 1300. Its 
shape gives an impression of rotation, but since it takes hundreds of 
millions of years to turn once around, we cannot hope to detect 
changes in this view during one man's lifetime, or even during the 
whole history of astronomy. Mount Wilson and Palomar Observatories 


So NGC 4594 

SBa NGC 2859 

Sb NGC 2841 

NGC 5457(M 101) 

SBb NGC 5850 

SBc NGC 7479 

The Life-Story of a Galaxy 

Figure VII-3. A barred spiral galaxy with a spiral nucleus, NGC 
1097. A normal barred spiral (SB) galaxy has a straight bar between 
two spiral arms (Figure V-)). The small spiral in the center of 
this one raises the question of how the bar can remain straight when 
a part of it is more rapidly rotating at the center. 

McDonald Observatory 

Another queer thing is shown in Figure VII-6; it looks unlike 
the galaxies we are used to and yet it certainly is a galaxy. It has 
two strings of material and a kind of loop. One would expect 
such an unstable structure soon to change; hence it is also likely 
to be young. 

In summary, it is difficult to understand in detail how one sort 
of galaxy can evolve into another, yet in a general way we know 
that it must happen. We know that the stars in a galaxy are 


Figure VII-4. A new galaxy forming near an elliptical, NGC 2444, 
2445. The bright patches to the left of the normal, presumably old, 
elliptical galaxy are glowing gas illuminated by young, blue giant 
Stars. McDonald Observatory 


The Life-Story of a Galaxy 

Figure VII-5. A pair of galaxies with tails, NGC 4676. The question 
here is how the tails can remain sticking out without "winding up" 
into spiral arms. The spectra show that each galaxy in this pair is 
rotating rapidly. McDonald Observatory 


Figure VII-6. A peculiar loop-galaxy, NGC 6621, 6622. Such a shape 
fits into no regular class of galaxies; it is a freak that appears to be 
unstable and therefore of short life in its present form. 

McDonald Obsen>atory 


The Life-Story of a Galaxy 

ageing (Chapters III and IV), and that the shapes of certain gal- 
axies (Figures VII-5 and VII-6) cannot last, as the motions in 
each galaxy go on — motions we have measured by Doppler 
shifts. This reasoning leads us to think that elliptical galaxies 
are older than spirals and irregular galaxies. But if we go on to 
say that all irregular galaxies turn into spirals after 100 million 
years, and that all spirals turn into ellipticals after a billion 
years, how can we explain mixed groups or close pairs of one 
spiral with one elliptical? How can elliptical galaxies be heavier 
than spirals? (Where did the added mass come from as a galaxy 

One possible explanation is that ageing does not always pro- 
ceed at the same rate. Perhaps in the "young" spirals we see 
among "old" ellipticals, something prevented for a long time 
the formation and ageing of stars. Perhaps the mass of a galaxy 
has an effect on how rapidly it ages, so that most of the heavy 
ones have already become "old" ellipticals. Irregular "young" 
galaxies seen close to "older" spirals or elliptical galaxies sug- 
gest that, whatever the cause, evolution goes on at different 
rates in different galaxies even when they are located close to 
each other in space. Two close galaxies in a double may be at 
widely different stages in their life-histories, even though they 
have the same age in years. In fact, there could well be many 
even younger galaxies that we cannot see — dark blobs of matter 
in which stars have not yet formed because of magnetic fields or 
low density or some other peculiar condition. These ideas of the 
evolution of galaxies can be fitted equally well into either the 
"Big-Bang" Theory or the "Steady-State" Theory. 

From all this you can see that we do not have an adequate 
theory of how galaxies evolve. More observations and much 
more theoretical study is needed. The subject of evolution of 
galaxies is a field in which we can expect great changes in the 
next few years. 


Bondi, a noted theoretical physicist and astronomer, 
presents the evidence for the over-all expansion of 
the universe, evidence which depends greatly on the 
observed red shift of light from distant galaxies. The 
number mentioned at the end of the paper, ten billion 
years, is sometimes picturesquely called the "age of 
the universe. " 

23 Expansion of the Universe 

Hermann Bondi 

An excerpt from his book Relativity and Common Sense: 
A New Approach to Einstein, 1 962. 

The most striking feature of the universe is probably 
its expansion. What exactly is the evidence for this and 
how strong is it? In Plate I we have a picture that dis- 
plays some of the evidence in striking form. A series of 
pictures of galaxies is shown in the left-hand column. 
They are all taken with the same telescope, using the 
same magnification. On the right-hand side we see the 
spectra of these galaxies. Now, first, what is a spectrum? 
It is well known that white light is a combination of all 
the colors and that it can be broken up into these colors 
by suitable aids; a rainbow is a familiar instance. A 
handier means is the use of a prism of glass or other 
suitable material; with its aid the whole band of colors 
of sunlight is spread out. If one uses a prism that spreads 
out the sunlight very clearly, then one notices that the 
colors do not form a smooth band and that in numerous 
places dark lines run across the spectrum. The origin 
of these lines is rather complicated. In the main they 
are due to the light from the sun shining through cooler 
gases of the sun's atmosphere, and these gases happen 
to be opaque to very particular colors, to thin lines, and 
so leave a part of the spectrum dark. The astronomer 
can use spectroscopes of great power to analyze the light 
of individual stars and also of individual galaxies. Natu- 
rally, particularly for the very distant galaxies, rather 
little light is available, and because of that, and for more 
technical reasons, the spectrum of a galaxy will not be 
nearly as clear as, say, the spectrum of the sun. Never- 
theless, a few of the very prominent dark lines do show 


Expansion of the Universe 

up, even in the spectra of these distant galaxies. The re- 
markable phenomenon that was discovered nearly forty 
years ago is that these lines are not where they ought 
to be, not where they are in the case of the sun, say, 
but they are displaced; they are shifted. The shift is al- 
ways toward the red and is indicated in the illustrations 
of the spectra in Plate I. You will notice that the fainter 
and smaller the galaxy looks, the greater the shift of the 
spectrum toward the red. This is a full description of 
the direct observational result. A red shift of the spec- 
trum is observed and is correlated with the apparent 
brightness of the galaxy, so that the fainter the galaxy, 
the greater the red shift. From here on we start on a 
series of interpretations. 

The Red Shift 

First, what can be the explanation of such a red shift? 
In what other circumstances are red shifts observed? 
The answer is that, but for one rather insignificant cause, 
the red shift always indicates a velocity of recession. Un- 
familiar as the phenomenon is in the case of light, it 
is commonly noticed in the case of sound. If a whistling 
railway train speeds past you, then you notice that, to 
your ears, the pitch of the whistle drops markedly as 
the train passes you. The reason for this is not difficult 
to understand. The whistle produces sound; sound is a 
vibration of the air in which pressure maxima and pres- 
sure minima succeed each other periodically; these travel 
toward your ears where they are turned into nerve im- 
pulses that enter your consciousness. While the train is 
approaching, each successive pressure maximum has a 
smaller distance to travel to reach you. Therefore, the 
time interval between the reception of the pressure max- 
ima will be less than the time interval between their 
emission. We say that the pitch of the note is raised. 
Conversely, when the train is receding from you, each 
successive pressure maximum has farther to travel and, 
therefore, the pressure maxima will reach your ear at 
intervals of time greater than the intervals at which they 
were emitted. Accordingly, the pitch is lower. How great 





:C«0N4 BC0E4LI' 





58.000 MilES PER SECOND 

plate I. The expansion of the universe is inferred from 
these and similar observations. The left-hand column 
shows galaxies at various distances photographed with 
the same magnification. In each photograph the galaxy 
appears as a diffuse object with its center in the middle of 
the picture, but the two most distant ones are marked by 
arrows for purposes of identification. The other diffuse 
objects in the photographs are other galaxies, the sharp 
ones being stars near to us. On the right are photographs 
of the diffuse-looking spectra of the galaxies stretching in 
each case from blue on the left to red on the right. The 
bright lines above and below each spectrum are produced 
in the laboratory and serve only as markers. The pair of 
dark lines in the spectrum of each galaxy above the tip 
of the arrow would be above the foot of the arrow if the 
source were at rest. 


Expansion of the Universe 

the raising or the lowering of the pitch is, depends on 
the ratio of the velocity of the train to the velocity of 
sound, which is about 1100 ft. per second. 

Very much the same thing happens with light, but 

here an increase in the pitch becomes noticed as a shift 
toward the violet; a decrease in the pitch becomes no- 
ticed as a shift toward the red. Also, the crucial velocity 
is now not that of sound, but the very much higher ve- 
locity of light at 186,000 miles per second. A red shift, 
therefore, indicates a velocity of recession of the source; 
a velocity standing to the velocity of light in the ratio 
given by the magnitude of the red shift— that is, by the 
change in wave length divided by the wave length. The 
velocities so derived from the observed red shifts are 
shown on the right-hand side of Plate I. Such a velocity 
of recession is, then, the only cause of the red shift that 
we can infer from our terrestrial knowledge of physics. 
What about the other characteristic of the picture, this 
time the characteristic of the photographs on the left, 
the increasing faintness and diminishing size? We all 
know that an object of a given brightness will look 
fainter the farther away it is. There is very little else in 
astronomy to guide us about the distances of these gal- 
axies which we see so very far away. Accordingly, if we 
interpret the faintness of the galaxies as indicators of 
their distances, and the red shift of the spectra as ve- 
locities of recession, then we find that the velocity of 
recession is proportional to the distance of the object 

Velocity of Receding Stars 

We have inferred a "velocity-distance law" from the 
red shift-brightness relation. For a long time physicists 
and astronomers felt rather uneasy about these enor- 
mous velocities of recession that seemed to follow from 
their observations. They argued that all our interpreta- 
tion was based on our local knowledge of physics, and 
that unknown effects might well occur in the depth of 
the universe that somehow falsify the picture that we 
receive. Nowadays, we have little patience with this type 


of argument. For the expansion of the universe is not 
merely given by the observation of the spectrum. We 
have also noted the remarkable uniformity of the uni- 
verse, how it looks the same in all directions around us 
if only we look sufficiently far. If, then, we suppose that 
the universe is, indeed, uniform on a very large scale, 
we can ask the mathematical question: How can it move 
and yet maintain its uniformity? The answer is that it 
can only move in such a way that the velocity of every 
object is in the line of sight and proportional to its dis- 
tance. This is the only type of motion that will maintain 
uniformity. Therefore, we are again driven to the con- 
clusion that an expansion with a velocity of recession 
proportional to distance is a natural consequence of the 
assumption of uniformity which is also based on obser- 
vation. Furthermore, if we try to form a theory of the 
universe, whichever way we do it, we always come up 
with the answer that it is almost bound to be in motion, 
with objects showing velocities proportional to their 

I must again stress the uniformity of the system. We 
are not in a privileged position on the basis of these 
assumptions, but in a typical one. The universe would 
present the same appearance to observers on any other 
galaxy. They would see the same effects; the same red 
shift-brightness relation. Though no one can be certain 
of anything in this field, we do see that there are different 
fines of argument all converging to the conclusion that 
the red shifts should indeed be taken as indicating ve- 
locities of recession proportional to the distance of the 
objects. If we divide the distance of any galaxy by its 
velocity of recession, we get the same number whatever 
galaxy we choose. That follows from the proportionality 
of velocity and distance. This number is a time, a time 
that, according to the most recent work, is about 10,000 
million years. In some way or other this is the charac- 
teristic time of the universe. 


Does mass, like electric charge, exist in both positive 
and negative forms? If so, negative mass must have 
the most extraordinary properties — but they could ex- 
plain the immense energies of the star-like objects 
known as quasars. 

24 Negative Mass 

Banesh Hoffmann 

An article from Science Journal, 1965. 


Only a rash man would assert categorically that negative mass exists. Yet 
he would be almost as rash if, equally categorically, he said that it does not. 
True, if negative mass exists it must have extraordinarily perplexing pro- 
perties. For example, if we pushed a piece of negative mass towards the left 
with our hand, it would move perversely towards the right; and, if that 
were not nonsense enough, as it moved towards the right we would not feel 
the negative mass resisting our thrust but actually aiding it. 

If the behaviour of negative mass is so seemingly nonsensical, why 
should one even think about it further? It has never been observed. 
Surely anyone who said that negative mass does not exist would be far less 
rash than one who thought that it might. 

So it would seem. Yet the history of science should give us pause. We 
have learned from bitter experience that what at first seems utter nonsense 
can prove to be excellent science. For instance, who would have believed, 
at one time, that no material object can possibly move faster than light ? 
Or that an electron is, in a sense, both a particle and a wave ? Or that 
when two people are in relative motion each finds that the other's clock 
runs slow compared with his own? Yet these, and many other such 
unlikely statements, are now part of the legitimate currency of science. 



Even so, why should we seriously contemplate the idea of negative mass? 
The recently discovered quasi-stellar radio sourcea provide an answer. 
These objects, often referred to as quasars, pose a stark problem simply 
because they are, intrinsically, by far the brightest objects in the heavens. 
Not that they dazzle the eye. They are much too far away to do that, 
despite their brilliance. Indeed they are invisible to the naked eye. 
Though we owe their recognition in the first instance to the radio astro- 
nomers, it would be incorrect to say that the radio astronomers were the 
first to detect them. The quasars had often been photographed by the 
optical astronomers. But on the photographs they looked like faint stars 
of no particular interest; and with so many more glamorous celestial 
objects demanding their attention the optical astronomers had simply 
ignored them. 

Whenever the radio astronomers detected a source of radio waves in the 
heavens they told their optical confreres who then directed their largest 


telescopes towards the region in question. For the most part all was neat 
and orderly: the optical astronomers found visible objects that were 
clearly the sources of the radio waves — usually galaxies of one sort or 
another. Sometimes they drew a blank. And just occasionally they could 
find nothing except a star-like object so faint that if it were indeed an 
ordinary star it could not have given rise to the relatively strong radio 
waves that had been observed. 

Nevertheless, more precise radio bearings confirmed that these star-likt 
objects were indeed the radio sources and from then on the puzzle grew 
until it reached massive proportions. In an expanding universe, the further- 
most objects recede the fastest and this recession is evidenced by a shift of 
spectral lines towards the red. The quasars were found to have spectral 
red shifts corresponding to recession speeds as high as half the speed of 
light, implying that they were among the most distant known objects in 
the universe. This was incredible, if they were stars, since there are 
theoretical limits to the size and brightness of a star and no star could be 
bright enough to be observable at such distances. If the distances were 
correct, individual quasars must be emitting light at more than a million 
million times the rate of emission of the Sun and, indeed, something like a 
hundred times the rate of emission of a complete giant galaxy. Yet the 
quasars could not be anywhere near the size of an average galaxy which is 
tens of thousands of light years across: they would look larger if they were 
indeed that large. Another reason, less obvious, is that some of the quasars 
have rapid fluctuations in brightness, with periods measurable in vears 
and even in weeks. Not only do galaxies maintain a steady bright less; 
there are also relativistic reasons for believing that an object whose 
brightness fluctuates with a period of a few years cannot be more than a 
few light years across. 

Thus, the astronomers were faced with a major problem: how could 
they account for the prodigious rate at which quasars were radiating 
energy, and what was the source of this energy ? 

Quasi-stellar radio source 3C 147 

In February of this year, there were 45 known quasars. By now the 
number is likely to be significantly larger. Several theories have been 
proposed to explain the nature of quasars and the source of their energy. 
Indeed, it is only with the recent advent of new observational techniques 
that the rate of discovery of quasars has significantly outstripped the rate 
of production of theories to account for their properties. If one tries to 
account for their spectacular brightness by conventional astrophysical 
processes, in terms of Einstein's relationship of energy to mass and the 
speed of light (E=mc % ), one is almost driven to assume it is due to a 
prodigious rate of supernova explosions ; even then one has to postulate 
enormous amounts of matter. 

I. S. Shklovsky and G. R. Burbidge, among others, have suggested ways 
in which such explosions might occur frequently. Also, G. B. Field has 
proposed that a quasar is just an early stage in the evolution of a regular 
galaxy having relatively small rotational energy, the extraordinary 
brightness arising from the. explosion of supernovae at the rate of about a 
hundred a year (the usual rate being one explosion every three or four 
hundred years in an average galaxy). Since the supernovae would explode 
at irregular intervals, this hypothesis could explain the fluctuating bright- 
ness but it would explain only the most rapid fluctuations and not one 
whose period was of the order of a decade. 

T. Gold has suggested that both the brightness and the fluctuations 
could come from frequent collisions of stars in a highly compact galaxy, 
the collisions tearing the stars open and exposing their glowing interiors. 

V. L. Ginzberg, among others, has looked to gravitation as a source of 
energy in the quasars. A tall building seems to be a placid unenergetic 
thing. But if its foundations crumble it falls to the ground with devastating 
effect. In its upright position it has stored gravitational energy — put there 
by the cranes that lifted the building blocks — and when it collapses this 
energy is released. We do not know how matter came into existence, but 
it is dispersed throughout the universe and, in its dispersed state, it has 
gravitational energy akin to that of the upright building. As portions of 
matter come together locally under the influence of their mutual gravi- 
tation they transform part of their gravitational energy into energy of 


Negative Mass 

Quasi-stellar radio source 3C 273 




motion. Under normal conditions the celestial object built up in this way 
does not collapse. Its rotation tends to make it fly apart and thus counter- 
acts the shrinking effect of gravitation. And if it does begin to collapse it 
usually tends to bounce back as the gravitational energy released is 
changed into motion. But F. Hoyle and W. A. Fowler, using the general 
theory of relativity, conceived of circumstances in which a gigantic 'star' 
might suffer a really radical gravitational collapse, becoming a relatively 
minuscule object of stupendous density. In the process it could give off 
light and radio energy at the observed quasar rate, but to do so the 'star' 
would have to contain an enormous amount of matter — a hundred 
million times that in the Sun. 

Because the amounts of energy involved verge on the incredible, J. 
Terrell has suggested that the quasars are actually quite close, in astro- 
nomical terms, being fleeing fragments formed as a result of an explosion 
within our own galaxy. If so they would be much smaller and much less 
bright than had been supposed. But then one would have to ascribe the 
large red shifts of their spectral lines not to cosmological recession velocities, 
arising from the overall expansion of the universe, but to local recession 
velocities produced solely by the initial explosion. Although the amount 
of energy involved in this hypothesis is considerably less than that needed 
to account for quasars as very distant objects, it is nevertheless alarmingly 
large for a relatively local explosion, and to account for it Terrell feels a 
need to invoke a local gravitational collapse. 

J. A. Wheeler has proposed yet another idea which he bases on the 
Einstein concept of curved space in a gravitational field. If only one could 
ignore rotation, a sufficiently large amount of matter would inevitably 
undergo radical gravitational collapse. As the matter fell together to a 
density of unheard of proportions, the curvature of space would increase 
locally until a sort of open pouch, or pocket, or blister was formed. The 
greater the amount of matter falling into it, the more rotund the blister 
would become and, as it grew more concentrated, its neck would become 
ever narrower. Eventually the neck would close and the blister would 
become a hidden cyst of space, with never an external pucker to reveal 
its presence. The matter that had fallen into it would be lost completely 
to the outside world. Not even its gravitational effect would survive. But 
in falling it could give up all its energy (mc*) to the main part of the 
quasar, and this could be the fuel that kept the fire burning so brightly. 

There is yet another possibility— if one can accept the idea of negative 
mass. For negative mass can act like a bank overdraft, allowing one to 
borrow energy for emergency purposes when high output is needed. And 
it has the considerable advantage over a bank overdraft that one can 
manage, in a sense, to avoid paying back what one has borrowed. 

Let us then, look more closely at the properties of negative mass, taking 
encouragement from the fact that neither the theory of relativity nor the 
quantum theory is a barrier to the existence of negative mass despite its 
awkward properties, and that negative mass can be excluded from those 
theories only by the arbitrary imposition of a ban from the outside. 
According to Newton, the gravitational attraction between two bodies is 
proportional to the product of their masses. If one of the masses is negative 
and the other positive, their product will be negative and therefore so, too, 
will the gravitational attraction between them. Since a negative attrac- 
tion is a repulsion, we might expect the two masses to accelerate away 
from each other. But this is not the case. Negative mass does not do the 
expected thing. Imagine the two masses placed side by side, the positive 
mass to the right of the negative mass. Their mutual gravitational 
repulsion accelerates the positive mass towards the nght, of course. 
But what of the repulsion that acts on the negative mass? Since it is 
directed towards the left, and since negative mass acts perversely, the 
repulsion will cause the negative mass to move towards the right, that is 
towards the positive mass. Thus both masses move towards the nght, the 
negative mass chasing the positive. Enormous speeds could be built up in 
the course of such a chase; and it seems that we would be getting some- 
thing for nothing— generating energy without doing work, and thus 
violating the law of conservation of energy. But in fact we would not. 
True the faster the positive mass goes, the greater its energy. But the 



same is not true of the negative mass. The faster it goes, the more deeply 
negative its energy becomes. So the negative mass can chase the positive 
mass and generate enormous speeds while the total amount of energy 
remains unchanged. 

Once the perversity of negative mass is grasped, it is not difficult to see 
that positive mass causes both positive and negative mass to accelerate 
towards it gravitationally, but that negative mass gravitationally causes 
all mass, whether positive or negative, to accelerate away from it. Again, 
if two particles have electric charges that are either both positive or both 
negative, the particle of negative mass will still chase the particle of 
positive mass; but if the charges have opposite signs the particle of positive 
mass will do the chasing, provided that the electrical force is larger than 
the gravitational. 

Thus, we begin to see that the idea of negative mass might help to 
explain the enormous brightness of the quasars. But it is not enough 
simply to postulate the existence of negative mass. We must be able to 
explain why it has not been observed and we must present a specific 
mechanism by which negative mass could indeed fuel the quasar furnaces. 



If negative mass exists we would expect all particles of positive mass to 
decay spontaneously into particles of negative mass, emitting radiation in 
the process and causing the material universe to blow up. Though this 
appears to be a formidable obstacle, we would be faint hearted to let it 
deflect us from our purpose. Indeed one needs no great courage, for 
theoretical physics has often been — and still is — plagued by similar 
theoretical catastrophes. 

Many decay mechanisms that one could argue as conceivable seem not 
to occur in nature. To account for such absences, theoretical physicists 
impose on their theories special conservation rules which forbid decays 
that the theories would otherwise permit. We can introduce an analogous 
conservation rule that would prevent particles of positive mass from 
decaying into particles of negative mass. 

But if we do, how are we ever going to general* particles of negative 
mass? Once again we take our cue from current .uomic theory. Some of 
the conservation rules are not inviol.ite. We therefore make ours breakable 
too — but only under exceptional conditions. 

Conservation rules are always related to symmetries and they are 
broken when the corresponding symmetries are marred. Since, according 
to Einstein, gravitation is a curvature of space-time, it could well warp 
symmetries. So we imagine that in the presence of an extremely strong 
gravitational field the conservation rule prohibiting the formation of 
negative mass can be broken; and we say that only under extreme con- 
ditions such as exist within a quasar is this likely to occur. 

Next we recall that gravitation is different from all other forces, in that 
gravitational waves are generated by mass and themselves transport mass. 
(Electromagnetic waves, for example, are generated by electric charge 
but do not transport electric charge.) So we postulate that positive rest 
mass can decay into negative rest mass only if the energy is given off in 
the form of gravitational waves. This has two important consequences. 
First, gravitational waves are generated when a particle is accelerated by 
non-gravitational forces, and these will be particularly powerful in the 
hot, dense interior of a quasar. So much so that, with the requirement of 
an intense gravitational field, we can effectively confine the production 
of negative mass to such extreme circumstances as are likely to exist in 
the interiors of quasars. 

The second consequence has to do with a curious asymmetry between 
positive and negative mass in Einstein's theory. Work by H. Bondi and 
others indicates that, irrespective of whether the matter producing the 
gravitational waves is positive or negative, the waves carry away only 
positive energy and thus only positive mass. So if a particle of, say, 6 
units mass gave off gravitational waves whose energy had mass 4, it would 
end up with mass 2. But if a particle of mass 2 gave off gravitational 
waves of mass 4 it would be left with mass of —2, that is, a negative mass. 
It could not now give off gravitational waves of mass —4 and return to a 


Negative Mass 

mass of + 2. If it gave off further gravitational waves of mass 4 it would 
go to mass —6 and so on. The process would slow down, however, since 
the more deeply negative the mass became the less easily would the 
particle be accelerated. 

The gravitational waves would be carrying energy to the more peri- 
pheral parts of the quasar while building up an energy deficit in the form 
of negative mass. Where, though, would the deficit be stored ? We might 
imagine that since matter of negative mass has negative density it would 
be far more buoyant than matter of positive mass and density. But once 
again the perversity of negative mass betrays our expectations. A particle 
of positive mass in a quasar would be pulled gravitationally towards the 
centre but buoyed up by the impacts of other particles. A particle of 
negative mass would also be accelerated gravitationally towards the 
centre but it would react perversely to the same impacts. It would there- 
fore plunge towards the centre, and there it would mix with positive mass 
to form a growing core whose average mass was zero. Here, then, at the 
centre of the quasar, the deficit would reside — and accumulate. If the 
above theory is at all close to actuality, it is no wonder that negative mass, 
if it exists, has not been observed. 

But we are taking too easy a way out, a way reminiscent of the White 
Knight in "Through the Looking Glass" who 

"... was thinking of a plan 
To dye one's whiskers green, 
And always use so large a fan 
That they could not be seen." 

The presence of a growing core of zero mass would increase the natural 
instability of a large celestial object. If an explosion occurred, negative 
mass could be ejected. What would happen to it ? It could not form stars 
of negative mass. Why not ? Because for negative mass gravitation is not 
a cohesive but a dispersive force. As a particle of negative mass travelled 
through space it would be attracted towards stars, and on falling into one 
would plunge to its centre. 

In the course of its travels, when it encountered particles of positive 
mass, especially if the negative and the positive particles were charged, the 
particle of negative mass would generate high velocities by the chasing 
process ; and if one of these fast moving particles of positive mass entered 
our atmosphere it could give rise to a shower of cosmic rays of very great 
energy. It is not completely impossible that cosmic ray showers of puzz- 
lingly high energy that have been observed might be due to such a cause. 

What if one of the particles of negative energy entered the detection 
apparatus of a cosmic ray experimenter ? This would be a rare event, 
since at best neither particles of negative mass nor cosmic ray experi- 
menters are abundant. But if a cosmic ray experimenter ever found 
evidence of a particle going in one direction but pushing in the opposite 
direction that would indeed be a decisive event for it would show that, 
despite the many theoretical problems to which it would give rise, negative 
mass does indeed exist. 


Quasi-stellar radio sources by J. L. Greenstein (in Scientific American, 209, 54, 
December 1963) . 

The international symposium on gravitational collapse (Lmvernty of 
Chicago Press, Chicago, 1965) 

Negative mass as a gravitational source op energy in the quasi-stellar 
radio sources by B. Hoffmann (essay obtainable from Gravity Research Foundation, 
Sew Boston, 1964) 


Mount Wilson and Palomar Observatories (page 75, bottom, and page 76, top) 


25 Fo ur Poetic Fragments About Astronomy 

From Troilus and Cressida William Shakespeare 

From Hudibras Samuel Butler 

My Father's Watch John Ciardi 

II Va Neiger . . . Francis Jammes 


The heavens themselves, the planets and this center, 

Observe degree, priority and place, 

Insisture, course, proportion, season, form, 

Office and custom, in all line of order: 

And therefore is the glorious planet Sol 

In noble eminence enthroned and sphered 

Amidst the other; whose medicinable eye 

Corrects the ill aspects of planets evil, 

And posts like the commandment of a king. 

Sans check to good and bad: but when the planets 

In evil mixture to disorder wander, 

What plagues and what portents, what mutiny, 

What raging of the sea, shaking of earth, 

Commotion in the winds, frights, changes, horrors, 

Divert and crack, rend and deracinate 

The unity and married calm of states 

Quite from their fixture! O, when degree is snaked, 

Which is the ladder to all high designs, 

The enterprise is sick! 

William Shakespeare 


Four Poetic Fragments About Astronomy 

Second Part, Canto HI 

The Egyptians say, The Sun has twice 

Shifted his setting and his rise; 

Twice has he risen in the West, 

As many times set in the East; 

But whether that be true, or no, 

The Devil any of you know. 

Some hold, the Heavens, like a Top, 

Are kept by Circulation up; 

And 'twere not for their wheeling round, 

They'd instantly fall to the ground: 

As sage Empedocles 'of old, 

And from him Modern Authors hold. 

Plato believ'd the Sun and Moon, 

Below all other Planets run. 

Some Mercury, some Venus seat 

Above the Sun himself in height. 

The learned Scaliger complain'd 

'Gainst what Copernicus maintain'd, 

That in Twelve hundred years, and odd, 

The Sun had left his antient Road, 

And nearer to the Earth, is come 

'Bove Fifty thousand miles from home. 

Samuel Butler 



One night I dreamed I was locked in my Father's watch 

With Ptolemy and twenty-one ruby stars 

Mounted on spheres and the Primum Mobile 

Coiled and gleaming to the end of space 

And the notched spheres eating each other's rinds 

To the last tooth of time, and the case closed. 

What dawns and sunsets clattered from the conveyer 

Over my head and his while the ruby stars 

Whirled rosettes about their golden poles. 

"Man, what a show!" I cried. "Infinite order!" 

Ptolemy sang. "The miracle of things 

Wound endlessly to the first energy 

From which all matter quickened and took place!" 

"What makes it shine so bright?" I leaned across 

Fast between two teeth and touched the mainspring. 

At once all hell broke loose. Over our heads 

Squadrons of band saws ripped at one another 

And broken teeth spewed meteors of flak 

From the red stars. You couldn't dream that din: 

I broke and ran past something into somewhere 

Beyond a glimpse of Ptolemy split open, 

And woke on a numbered dial where two black swords 

Spun under a crystal dome. There, looking up 

In one flash as the two swords closed and came, 

I saw my Father's face frown through the glass. 

John Ciardi 


Four Poetic Fragments About Astronomy 

/romlLVANEIGER.. . 

On a baptise les etoiles san penser 
Qu'elles n'avaient pas besoin de nom, et les nombres 
Qui prouvent que les belles cometes dans l'ombre 
Passeront, ne les forceront pas a passer 

Francis Jammes 


The imagination of scientists often exceeds that of the 
science fiction writer. The question asked is how an advanced 
technological civilization could capture most of the sun's 
energy. (See note above title of article 19.) 

26 The Dyson Sphere 

I. S. Shklovskii and Carl Sagan 

An excerpt from Intelligent Life in the Universe, 1966. 

To discuss another possible modification of the cosmos by the activities of 
intelligent beings, consider the following question: Is it possible that in the future — 
perhaps the distant future — man could so change the solar system that his activities 
would be visible over interstellar distances? In Chapter 11, we discussed the 
difficulties in the detection of planets about even the nearest stars, with present 
techniques. But what of the future? Is it possible that someday we shall be able to 
conclude, from observed characteristics, that a star is accompanied by a planet 
populated by an advanced technical civilization? Let us consider some of the ideas 
of Constantin Edwardovich Tsiolkovskii, an illustrious Russian pioneer in problems 
of space exploration. 

Three quarters of a century ago, this remarkable man suggested a plan for the 
rebuilding and reorganization of the solar system. In his book Dreams of the Earth 
and Sky, published in 1895, he pointed out that the Earth receives only 5 x 10~ 10 of 
the total flux of solar radiation. He speculated that eventually mankind would 
make use of all the heat and light of the Sun by colonizing the entire solar system. 
Tsiolkovskii suggested that first the asteroids be rebuilt. The intelligent beings of 
the future, he predicted, would control the motion of these small planets "in the 
same way that we drive horses." The energy necessary to maintain the inhabitants 
of the asteroids would come from "solar motors." Thus, we see that over 70 years 
ago, Tsiolkovskii predicted the invention of the solar battery, a device which is 
presently used to provide energy for space vehicles. 

The transformed asteroids would form a chain of space cities. The construc- 
tion materials would initially come from the asteroids themselves, "the mass of 
which would be dismantled in a day." V Tsiolkovskii's ideas on the re-engineering 
and relocation of the asteroids have been echoed in recent years by the American 
engineer Dandridge Cole, of the General Electric Corporation. A After the 
asteroidal material is exhausted, Tsiolkovskii envisions the rebuilding of the Moon. 
He allows several hundred years for this project. Then, the Earth and the larger 
planets would be reorganized. According to Tsiolkovskii, the entire transformation 
of the solar system would require hundreds of thousands — perhaps millions — of 
years. This plan would provide enough heat and light to support a population of 
3 x 10 21 manlike beings — approximately 10 14 more people than presently inhabit 
the Earth. 


The Dyson Sphere 

Although to his contemporaries the daring ideas of Tsiolkovskii seemed to be 
merely the daydreams of a provincial school-teacher, his brilliant foresight is readily 
appreciated today. The eminent American theoretical physicist Freeman J. Dyson, 
of the Institute for Advanced Study, Princeton, basing his theories on the 
achievements of contemporary science, has recently independently repeated many 
of Tsiolkovskii's ideas, without knowing anything of the Russian's work. 

Dyson, in a most interesting article published in 1960, attempted to perform a 
quantitative analysis of the problem of rebuilding the solar system. He first 
discussed the fact that scientific and technological development takes place very 
rapidly, after a society has entered its technological phase. The timescale of such 
development is insignificant, compared with astronomical and geological time- 
scales. Dyson concluded that the one important factor which restricts the scientific 
and technical development of an intelligent society is the limited available supply of 
matter and energy resources. At present, the material resources which can be 
exploited by man are limited roughly to the biosphere of the Earth, which has a 
mass V estimated variously between 5 x 10' 7 and 5 x 10' 9 gm A — that is, less than 
10 s the mass of the Earth. The energy required by contemporary mankind per 
year is approximately equal to that which is liberated in the combustion of 1 to 2 
billion tons of hard anthracite coal per year. In terms of heat, we find that 
contemporary man is expending an average of 3 x 10 19 erg sec" 1 . The Earth's 
resources of coal, oil, and other fossil fuels will be exhausted in a few centuries. 

The question of our reserves of matter and energy becomes more acute when 
we consider the prospective long-term technological development of our society. 
Even if we assume that the average annual growth rate in production is only one- 
third of a percent (a very small figure, when compared to the annual growth rate 
V of a few percent in modern industrial societies A), our productivity will double 
in about a century. In 1000 years, the rate of manufacture will increase by 20,000 
times; and in 2500 years, by 10 billion times. This means that the energy require- 
ments in 2500 years will be 3 x 10' 9 erg sec" 1 , or approximately 0.01 percent of 
the entire luminosity of the Sun. This figure is approaching cosmic proportions. Will 
all of our energy resources have been exhausted by the time we achieve this level 
of productivity? 

To answer this question, let us now consider the material resources which are 
conceivably available to mankind in the future. We shall — perhaps optimistically 
— assume that we will be able to achieve controlled thermonuclear reactions. The 
total amount of hydrogen in the Earth's hydrosphere is approximately 3 x 10 23 
grams, while the amount of deuterium is approximately 5 x 10 19 grams. Deute- 
rium would be the basic fuel of a thermonuclear reactor. The amount of energy 
released by reaction of all the available deuterium would be about 5 x 10 38 ergs. 
In 2500 years, this amount of energy — still assuming an increase in production of 
one-third of a percent per annum — would be sufficient for only a 50-year period. 
Even if we assume that controlled thermonuclear fusion can eventually be fueled by 
ordinary hydrogen, and that 10 percent of the world's oceans can be utilized as an 
energy source — to burn more would probably be inexpedient — in 2500 years we 
would be able to provide only enough energy for another few thousand years. 

Another possible energy source would be the direct utilization of solar 
radiation. Each second, approximately 2 x 10 J4 ergs of solar radiation fall upon 
the surface of the Earth. This is almost 100,000 times more than the current 
production of all forms of energy. Yet it is 100,000 times less than the estimated 


energy requirements for the year 4500 a.d. Thus, direct solar radiation is 
inadequate to support a stable and sustained increase in production of only one- 
third of a percent per annum, over a long period of time. From this discussion, we 
can conclude that the energy resources of the Earth are insufficient to fulfil the long- 
term requirements of a developing technological society. 

Before considering this question further, let us make a slight digression. A 
hypercritical reader may claim that the above calculations are similar to the 
discussions of the English clergyman Thomas Malthus. This is, however, not 
the case. Malthus predicted that world population growth would outstrip the 
development of productive forces, and that this would lead to a progressive 
deterioration of living conditions. His proposed solution was that the poorer 
classes — that is, the working classes — lower their birthrate. Malthus' views are 
invalid, because in an intelligent, organized society, the increase of productive 
forces always outstrips the increase in population. The population of a nation is 
related, sometimes in a complex way, to its productivity, and in fact is ultimately 
determined by it. Our discussion of future energy budgets bears no relation to the 
Malthusian doctrine. We have been discussing only the possibilities of the increase 
in the productive capacities of a society, which is naturally limited to the material 
and energy resources available. 

V The exponential increase in the population of the Earth during historical 
times is indicated schematically in Fig. 34-1 . The required future productive capacity 
of our society is dramatically illustrated — assuming no major population self-limita- 
tion occurs — by extrapolation of the curve to the future. A 

Let us ask another question : Will there in fact be any appreciable increase in 
the future productive capability of our society? What is the basis for assuming that 
mankind's progress will be directly related to an increase in his productive capacity? 

Figure 34-1. Estimated past and extrapolated future rates of human population growth, 
planet Earth. 


The Dyson Sphere 

Perhaps development will be in terms of qualitative, not quantitative, changes. 
These problems are philosophical in nature and cannot be discussed in detail here. 
However, I would like to state that I believe it to be impossible for a society to 
develop without a concurrent increase in production, both qualitatively and 
quantitatively. If an increase in productivity were eliminated, the society would 
eventually die. Note that if a society were to consciously interrupt its productive 
development, it would have to maintain a very precise level of production. Even 
the slightest progressive decrease would, after thousands of years reduce the tech- 
nological potential to essentially nothing. Over these timescales, any civilization 
which consciously resolves to maintain a constant level of productivity would be 
balancing on a knife-edge. 

Let us now return to the subject of the material resources available to a 
developing society. After reaching a high state of technical development, it would 
seem very natural that a civilization would strive to make use of energy and 
materials external to the planet of origin, but within the limits of the local solar 
system. Our star radiates 4 x 10" ergs of energy each second, and the masses of 
the Jovian planets constitute the major potential source of material. Jupiter alone 
has a mass of 2 x 10 ! " grams. It has been estimated that about 10" ergs of energy 
would be required to completely vaporize Jupiter. This is roughly equal to the total 
radiation output of the Sun over a period of 800 years. 

According to Dyson, the mass of Jupiter could be used to construct an 
immense shell which would surround the Sun, and have a radius of about 1 A.U. 
( 150 million kilometers). V How thick would the shell of a Dyson sphere be? The 
volume of such a sphere would be A-nrS, where r is the radius of the sphere, 1 
A.U., and S is its thickness. The mass of the sphere is just the volume times its 
density, p, and the mass available is approximately the mass of Jupiter. Thus, 
4-rrrpS — 2 x 10" grams. Thus, we find that pS ~ 200 gm enr 2 A of surface area 
would be sufficient to make the inner shell habitable. We recall that the mass of the 
atmosphere above each square centimeter of the Earth's surface is close to 1000 
gm. V If the over-all density of the shell were 1 gm cm" 3 or slightly less, the 
thickness of the shell, S, would be a few meters. A Man today, for all practical 
purposes, is a two-dimensional being, since he utilizes only the surface of the 
Earth. It would be entirely possible for mankind in the future — say, in 2500 to 
3000 years — to create an artificial biosphere on the inner surface of a Dyson 
sphere. After man has accomplished this magnificent achievement, he would be 
able to use the total energy output of the Sun. V Every photon emitted by the Sun 
would be absorbed by the Dyson sphere, and could be utilized productively. A The 
inside surface area of the Dyson sphere would be approximately 1 billion times 
greater than the surface area of the Earth. The sphere could sustain a population 
great enough to fulfil the predictions made by Tsiolkovskii three quarters of a 
century ago. 

We shall not at this time enter into a discussion of how such a sphere would be 
constructed, how it would rotate, or how we would guarantee that the inhabitants 
would not fall into the Sun. The fact is that the sphere would have different 
gravitational characteristics from those of a solid body. These problems, although 
complex, are not the principal problems. Dyson himself gave special attention to 
one interesting circumstance: A number of completely independent parameters — 
the mass of Jupiter, the thickness of an artificial biosphere, the total energy of 
the solar radiation, and the period of technological development — all, in Dyson's 


have consistent orders of magnitude. ... It seems, then, a reasonahle expec- 
tation that harring accidents, Malthusian pressures will ultimately drive an in- 
telligent species to adopt some such efficient exploitation of its available resources. 
One should expect that within a few thousand years of its entering the stage of 
industrial development, any intelligent species should be found occupying an 
artificial biosphere which completely surrounds its parent star. 

Up to this point, Dyson's speculations have been essentially the same as those 
of Tsiolkovskii, but based upon more recent scientific knowledge. At this point, 
Dyson introduces an idea novel V even to Tsiolkovskii A: How will a civilization 
living on the inner surface of a sphere surrounding its star appear from outside? 
Dyson says: 

If the foregoing argument is accepted, then the search for extraterrestrial intelli- 
gent beings should not be confined to the neighborhood of visible stars. The most 
likely habitat for such beings would be a dark object having a size comparable 
to the Earth's orbit, and a surface temperature of 200 to 300°K. Such a dark 
object would be radiating as copiously as the star which is hidden inside it, but 
the radiation would be in the far infrared, at about 10^ wavelength. 

If this were not the case, then the radiation produced by the star inside the 
shell would accumulate, and produce catastrophically high temperatures. 

Since an extraplanetary civilization surrounded by a Dyson sphere would be a 
very powerful source of infrared radiation, and since the atmosphere of the Earth is 
transparent to radiation between 8 and 13/*, it would be possible to search for such 
infrared stars with existing telescopes on the Earth's surface. V The sensitivity of 
contemporary infrared detectors is such that with the use of large telescopes, Dyson 
spheres could be detected over distances of hundreds of light-years even today. 
However, there is not necessarily any way of distinguishing a Dyson sphere detected 
at 8-13^ from a natural object such as a protostar, contracting towards the main 
sequence, and emitting infrared radiation with the same intensity. If the sky were 
mapped in the infrared for possible Dyson spheres, each radiation source could then 
be investigated by other techniques for characteristic radiation of an intelligent 
species — for example, at the 21 cm radio frequency. A 

It is also possible that Dyson civilizations might be detected by existing optical 

Such radiation might be seen in the neighborhood of a visible star, under cither 
of two conditions: A race of intelligent beings might be unable to exploit fully the 
energy radiated by their star because of an insufficiency of accessible matter, 
or they might live in an artificial biosphere surrounding one star of a multiple 
system, in which one or more component stars are unsuitable for exploitation 
and would still be visible to us. It is impossible to guess the probability that 
either of these circumstances could arise for a particular race of extraterrestrial 
intelligent beings, but it is reasonable to begin the search for infrared radiation 
of artificial origin by looking in the direction of nearby visible stars, and especially 
in the direction of stars which are known to be binaries with invisible companions. 

Dyson's idea is notable for the fact that it presents a specific example of how 
the activity of an intelligent society might change a planetary system to such an 
extent that the transformation would be detectable over interstellar distances. But 
a Dyson sphere is not the only way a civilization can utilize the available energy 
resources of its planetary system. There are other sources which may be even more 
effective than the complete utilization of local solar radiation. 


The Dyson Sphere 

First we shall consider using the mass of the large planets as a fuel for 
thermonuclear reactors. The Jovian planets consist primarily of hydrogen. The 
mass of Jupiter is 2 x 10 3 " gm, and the store of energy which would be released 
from the conversion of this quantity of hydrogen into helium would be approxi- 
mately 10 49 ergs, a vast amount of energy comparable to that released in a 
supernova explosion. If this energy were liberated gradually, over a long period of 
time— for example, at a rate of 4 x 10 33 erg sec 1 , comparable to the present solar 
luminosity— it would last for nearly 300 million years, a time span most likely 
greater than the life of the technical civilization itself. 

Perhaps a highly developed civilization could also use a fraction of its own star 
as an energy source. For example, it might be possible to "borrow" a few percent 
of the solar mass without any significant decrease in luminosity. Certainly, we do 
not yet know the methods for arranging such a loan, but it would probably be 
accomplished gradually. The conversion of, say, 5 x 10 31 gm of solar hydrogen 
—25 times more than the mass of Jupiter— would provide some 3 x 10 50 ergs, an 
energy supply adequate to satisfy the requirements of a technical civilization for 

several billion years. 

It is also conceivable, but much less likely, that such utilization of the mass of 
a star would occur at a more rapid pace, perhaps regulated so that the lifetime of 
the star would correspond to the lifetime of the civilization. The spectral 
characteristics of such a star would slowly vary. At the time that the star finally 
was turned off, the civilization would cease to exist. V But while we can imagine 
such a cosmic Gotterdammerung, it is not likely to be staged often. A 

If intelligent use is made of the enormous stores of energy available in the 
solar system, it would not be necessary to construct a Dyson sphere about the Sun. 
Assume, for example, that half the mass of the Jovian planets were used to 
construct artificial satellites, the "space cities" of Tsiolkovskii. These cities would 
be established in orbits close to the Sun. We may imagine thermonuclear reactors 
installed in these satellites and fueled by the remaining material in the Jovian 
planets. This picture preserves the essential direction of the development of a 
technical civilization envisioned in Dreams of the Earth and Sky, but it adds 
controlled thermonuclear reactions as an energy source. 

Now given these enormous controlled energy sources, civilizations could 
expand their activities on a much larger scale. We shall presently consider several 
additional ways in which a civilization might announce its presence over interstellar 
distances. These methods seem fantastic. We wish to emphasize that we are not 
saying that such methods are actually in existence; but the probability of their 
existence is not zero. V And what we have encompassed as fantas tic has 
declined progressively with the centuries. A The fundamental point is that the 
possibilities open to advanced technical civilizations are almost unlimited. 


Authors and Artists 


Isaac Asimov, born in 1920 in Petrovichi, Russia, 
came to the United States at the age of three, He 
graduated from Columbia University in 1939, and 
received his Ph.D. there in 1948. Since 1949 he 
has been in the department of Biochemistry at 
Boston University. Pebble in the Sky , Asimov'S 
first book, published in 1950, started him on a 
prolific career of writing for the layman. For his 
contribution in explaining science to the public 
he won the James T. Grady Award of the American 
Chemical Society in 1965. He is also well known 
as a writer of science fiction. 


Hermann Bondi, Professor of Applied Mathematics 
at King's College, University of London, was born 
in Vienna in 1919, and received his education at 
Trinity College, Cambridge (B.A. 1940, M.A. 1944). 
He also taught and did research in the United States. 
Professor Bondi's interests are the composition of 
stars, cosmology, and geophysics. 


Margaret Burbidge often works with her husband, 
an astrophysicist, as a husband-and-wife team. 
The Burbidges met and married while she, an 
astronomer, was working at the University of 
London Observatory, and he, a physicist, was 
studying meson physics at the same university. 
They have held appointments successively at 
Mt. Wilson and Palomar Observatories and the 
University of Chicago's Yerkes Observatory at 
Williams Bay, Wisconsin. Currently they are in 
the physics department of the University of Cali- 
fornia at San Diego, and are frequent contributors 
to scientific journals. 


Samuel Butler (1612-1680), the English satirist, 
was born at Strensham, Worcestershire. After the 
Restoration he became successively Secretary to 
Earl of Carbery, Steward of Ludlow Castle, and 
then a full-time writer. Between 1663 and 1678 he 
published the three parts of his most famous work, 
Hudibros. Just as Cervantes in his Don Quixote 
satirized the fanaticism of knight errantry, Butler 
in his Hudi bras , a burlesque heroic poem, ridiculed 
the fanaticism, pretentiousness, pedantry, and hypo- 
crisy of the Puritans of his time. 


John Ciardi, a poet and an educator, was born in 
Boston in 1916. His bachelor's degree is from Tufts, 
and he has a master's degree from the University of 
Michigan. He has taught at Kansas City, Harvard, 
and Rutgers. He is the director of the Bread Loaf 
Writers Conference and the poetry editor of the 
Saturday Review . Recipient of many awards in poetry, 
including the Prix de Rome, his works include 
Homeward to America , Other Ski es , Live Another 
Day, I Marry You . 


Arthur C. Clarke, British scientist and writer, is a 
Fellow of the Royal Astronomical Society. During 
World War II he served as technical officer in 
charge of the first aircraft ground-controlled ap- 
proach project. He has won the Kalinga Prize, 
given by UNESCO for the popularization of science. 
The feasibility of many of the current space devel- 
opments was perceived and outlined by Clarke in 
the 1930's. His science fiction novels include 
Childhoods End and The City and the Stors. 


I. Bernard Cohen was born in Far Rockaway, New 
York, in 1914. At Harvard he received a B.S. in 
1937 and a Ph.D in history of science in 1947. 
Since then he has been on the Harvard faculty 
in the history of science. He has been editor of 
I si s , the journal of the History of Science Society, 
and has written many books and papers in his field, 
among them a number of studies of Newton's works. 


Edward U. Condon was born in Alamogordo, New 
Mexico, in 1902 and obtained his degrees from the 
University of California. After teaching physics 
at Princeton, he became the director of the U.S. 
National Bureau of Standards for six years. Among 
his subsequent positions were a professorship of 
Physics at Washington University (St. Louis, Mo.) 
and one at the University of Colorado. In 1945—46 
he was the science advisor to the Special Committee 
on atomic energy of the 79th Congress. His research 
interests include quantum mechanics, atomic and 
molecular spectra, nuclear physi cs, micro-wave 
radio, and solid state physics. 




Henry S. F. Cooper, Jr., writer for the New Yorker 
since 1956, was educated at Phillips Acodemy, 
Andover, and at Yale University. At Yale he took 
a course in astronomy from Harlan Smith, and this 
led him to write an article about Professor Smith. 
This article, in part, started his writing career for 
the New Yorker. 


See Unit 2 Text, Section 6.1 


Jean Baptiste Camille Corot (1796-1875), one of 
the greatest nineteenth»century landscape 
painters of France, was born in Paris and studied 
at the Lycee de Louen. Corot was one of the first 
to paint out-of-doors. He traveled extensively 
throughout the continent. Corot's works are ad- 
mired for their idyllic romanticism injected into 
the paintings of mountains, cathedral s, and vil- 
lages. His "Chartres Cathedral," "Chateau de 
Rosny," and "Belfry at Douai," all in the 
Louvre, exemplify his touch. 


Robert H. Dicke, Professor of Physics at Princeton, 
was born in St. Louis, Missouri, in 1916, and he 
earned his Ph.D. at Rochester University in 1941. 
He was a staff member of the Radiation Laboratory 
at Massachusetts Institute of Technology during 
World War II. Dr. Dicke is widely known for his 
studies in gravitation, relativity, geophysics, and 


Stephen H. Dole is a researcher for the RAND 
Corporation. Born in West Orange, New Jersey in 
1916, he attended Lafayette and the United States 
Naval Academy. Presently he is a member of the 
steering committee for the Group for Extraterrestrial 
Resources. His work has dealt with chemistry and 
space programs; he studies oxygen recovery, human 
ecology in space flight, properties of planets, and 
origin of planetary systems. 

Richard Phillips Feynman was born in New York 
in 1918, and graduated from the Massachusetts 
Institute of Technology in 1939. He received his 
doctorate in theoretical physics from Princeton in 
1942, and worked at Los Alamos during the Second 
World War. From 1945 to 1951 he taught at Cornell, 
and since 1951 has been Tolman Professor of 
Physics at the California Institute of Technology. 
Professor Feynman received the Albert Einstein 
Award in 1954, and in 1965 was named a Foreign 
Member of the Royal Society. In 1966 he was 
awarded the Nobel Prize in Physics, which he 
shared with Shinchero Tomonaga and Julian 
Schwinger, for work in quantum field theory. 


Anatole France (1844—1924) was the nom de plume 
of Anatole Francois Thibault. The son of a book- 
seller, he began his productive literary career as 
a publisher's reader, "blurb" writer, and critic. 
Under the patronage of Madame de Calillavet, he 
published numerous novels, such as Le Li vre de 
Mon Ami . His early writings were graceful. Later 
they grew skeptical and solipsistic, as in Les 
Opinions de Jerome Cognord. In 1886 France was 
elected to the French Academy, and in 1921 he 
was awarded the Nobel Prize for Literature. 

See Unit 1, Section 2.2 


Charles Coulston Gillispie, born in 1918 in 
Harrisburg, Pennsylvania, was educated at 
Wesleyan, Massachusetts Institute of Technology, 
and Harvard. After teaching at Harvard, he went 
to Princeton, where he is now Professor of His- 
tory. He has been president of the History of 
Science Society, and a Fellow of the American 
Academy of Arts and Sciences, and member of the 
Academie Internationale d'Histoire Des Sciences. 
His books include Genesis and Geology , A 
Diderto Pictorial Encyclopedia , and The Edge 
of Objecti vi ty. 


Authors and Artists 


Owtn Joy Gingorich, born in Washington, Iowa, in 
1930, is an astrophysicist and historian of astro- 
nomy at the Smithsonian Astrophysical Observatory 
in Cambridge, Massachusetts. Among his respon- 
sibilities has been the task of directing the Central 
Bureau for Astronomical Telegrams, the world 
clearing house for comets, sponsored by the Inter- 
national Astronomical Union. He is interested in 
applying computers to the history of astronomy, and 
his translation from Kepler's Astronomia Nova , pub- 
lished for the first time in this Reader, was aided 
by a Latin dictionary program on an I.B.M. 7094 


Banesh Hoffmann, born in Richmond, England, in 
1906, attended Oxford and Princeton. He has been 
a member of the Institute of Advanced Study, elec- 
trical engineer at the Federal Telephone and Radio 
Laboratories, researcher at King's College, London, 
and a consultant for Westinghouse Electric Cor- 
poration's science talent search tests. He has won 
the distinguished teacher award at Queen's College, 
where he is Professor of Mathematics. During the 
1966-1967 year he was on the staff of Harvard 
Project Physics. 


Gerald Holton received his early education in 
Vienna, at Oxford, and at Wesleyan University, 
Connecticut. He has been at Harvard University 
since receiving his Ph.D. degree in physics there 
in 1948; he is Professor of Physics, teaching 
courses in physics as well as in the history of 
science. He was the founding editor of the 
quarterly Daedalus . Professor Holton's experi- 
mental research is on the properties of matter 
under high pressure. He is a co-director of 
Harvard Project Physics. 


Fred Hoyle is an English theoretical astronomer, 
born in Yorkshire in 1915. Now Professor of Astro- 
nomy at Cambridge University, he is perhaps best 
known for one of the major theories on the structure 
of the universe, the steady state theory. Hoyle is 
well known for his scientific writing, and his suc- 
cess in elucidating recondite matters for the layman. 


Francis Jammes was a French poet whose verses 
celebrate the pure and simple life. He was born on 
December 2, 1868 in Tournay. After his education 
in Bordeaux and Pau, he became a lawyer's clerk. 
He began writing at an early age and published his 
first work in 1898. He spent the latter port of his 
life in the city of Hasparren in the Basque country. 
He devised a compelling kind of free verse, using 
lines of varying lengths. Some of his favorite 
topics include the simple country folk of the 
Pyrenees, animals, young girls, as well as re- 
ligious themes. He died in 1938. 


See Unit 2 Text, Section 7.1. 


Paul Klee (1879-1940), one of the most imaginative 
painters of the twentieth century, was born near 
Berne, Switzerland. He taught at the Bauhaus, the 
influential German art and design school in Weimar. 
Klee's style is unbounded by tradition: his figures 
are visually unrealistic, his space and design seem 
incoherent, and his colors are symbolic and emotional 
rather than descriptive. 


Robert B. Leighton, born in Detroit, Michigan in 
1919, was first a student and then a faculty member 
at California Institute of Technology. He is a mem- 
ber of the International Astronomical Union, the 
National Academy of Science and the American 
Physics Society. Professor Leighton's work deals 
with the theory of solids, cosmic rays, high energy 
physics, and solar physics. 




Richard Lippold, sculptor, was born in Milwaukee 
in 1915. He attended the University of Chicago 
and graduated from the Art Institute of Chicago 
with a B.F.A. degree in 1937. Since graduating 
he has taught at the Layton School of Art in 
Milwaukee, the University of Michigan, Goddard 
College, served as head of the art section of the 
Trenton Junior College from 1948-52, and since 
1952 has been a professor at Hunter College in 
New York. His works have been exhibited inter- 
nationally, and frequently in the Whitney Museum 
in New York City. He has hod several one-man 
shows at the Willard Gallery. In 1953 he was 
awarded third prize in the International Sculpture 
Competition, Institute of Contemporary Arts, 
London, and in 1958 the Creative Arts award from 
Brandeis University. He is a member of the 
National Institute of Arts and Letters. 


Terry Morris, a free-lance magazine writer since 
1951, was bom in New York City. After earning 
her B.A. and M.A. in English, she taught English 
for six years in New York high schools. During 
World War II, her husband in the service, she 
wrote her experiences as an army wife in her 
first article, "Armytown, U.S.A." in The New 
Republic , wnich wos expanded info a novel 
No H.ding Place (1945) at publisher Alfred A. 
Knopf's suggestion. Her work has appeared in 
many American and foreign magazines, and she 
has also worked for newspapers, radio and 
televi sion. 


See Unit 2 Text, Section 8.1- 


Pablo Ruiz Picasso, the initiotor (with Georges 
Braque) of Cubism and probably the most seminal 
contributor in twentieth century ort, wos born at 
Malaga, Spain in 1881. After lessons in art from 
his father, an artist and professor at the Academy 
of the Arts in Barcelona, Picasso settled in Poris. 
His early paintings were somber pictures, many of 
the life of a circus or o big city. But after 1905 
he evolved toward Cubism. Picasso moved uwo y 
from three-dimensionol perspective and created a 
surrealistic two-dimensional picture. Perhaps his 
most famous picture is "Guernica" (at the Museum 
of Modern Art in New York), his reaction to the 
bombing of civilians in the Spanish Civil War. 

Peter Guy Roll wos born in Detroit, Michigan, In 
1933. At Yale he received his B. S. , M.S., and 
Ph.D. He worked as Junior Scientist on the design 
of a nuclear reactor for the Westinghouse Atomic 
Power Division. After teaching and research ex- 
perience at Yale, Princeton, and the University 
of Michigan, he became Associate Professor of 
Physics at the University of Minnesota. He has 
also been a staff physicist for the Commission on 
College Physics. 


Carl Sagan, born in 1921, is Assistant Professor 
of Astronomy at Harvard University and a staff 
member of the Smithsonian A strophy si cal Obser- 
votory. He has made significant contributions to 
studies of planets, of the origin of life, and of the 
possibil ities of extraterrestrial life. An experi- 
menter on the Mariner 2 Venus misson, he has 
served on advisory committees for the National 
Academy of Sciences and for the National Aero- 
nautics and Space Administration. 


Matthew Sands was born in Oxford, Massachusetts, 
in 1919. He attended Clork College, Rice Institute, 
and Massachusetts Institute of Technology. During 
World War II he worked at the Los Alamos Scic"'' 
Laboratory. He was Professor of Physics at the 
California Institute of Technology before |ommg 
the linear accelerator group at Stanford University. 
Professor Sands specializes in electronic instru- 
mentation for nuclear physics, cosmic rays, and 
high-energy physics. He served os chamiuin el 
the Commission on College Physics. 


Georges Seurat (1859-1891) wos educated ot 
Ecole des Beaux-Arts. His most famous painting, 
"Un Dimonche d'Ete a la Grande Jette" (Chicago 
Aft Institute) exemplified his characteristic tech- 
nique of Pointillion painting with o very large 
number of small spots of strong primary colors 
mixed only with white. Seurat is considered to 
be a neo-impressioni st owing to his use of 
orderly fundamental structures — a form anta- 
gonistic to the intuitive method of the Im- 
pressioni sts. 

WILLIAM SHAKESPEARE (1564-1616) needs 
no introduction. 


Authors and Artists 


I. S. Shklovskii is a staff member of the Sternberg 
Astronomical Institute of the Soviet Academy of 
Sciences, Moscow. One of the world's leading 
astrophycists, he has played a major role in 
Soviet space achievements and in radio astronomy. 
His books include Physics of the Solar Corona, 
Cosmic Radio Waves, and Intelligent Life in the 
Universe. He is a Fellow of the Royal Astro- 
nautical Society of Great Britain, and a Corres- 
ponding Member of the Soviet Academy of 


Joseph Weber, now Professor of Physics at the 
University of Maryland, was born in Paterson, 
New Jersey, in 1919. He received his B.S. at the 
United States Naval Academy, and his Ph.D. from 
the Catholic University of America. He has been 
a fellow at the Institute of Advanced Study, a 
Guggenheim Fellow, and a Fellow at the Lorenz 
Institute of Theoretical Physics at the Univer- 
sity of Leyden, Holland. 


Wolter S. Sullivan was born in New York City in 
January of 1918. He received a BA from Yale in 
1940 and joined the staff of the New York Times 
in the same year. He was first a foreign corres- 
pondent but then turned his interest to reporting 
science. He has been the Science Editor of the 
Times since 1964, and has also published 
several books. Mr. Sullivan has two daughters 
and a son, and currently lives in Riverside,