The Project Physics Course
Reader
2
Motion in the Heavens
The Project Physics Course
Reader
UNIT
2 Motion in the Heavens
A Component of the
Project Physics Course
Published by
HOLT, RINEHART and WINSTON, Inc.
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
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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
permission.
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
permission.
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
permission.
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.
in
IV
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
62
65
9 Newton and the Principia 68
C. C. Gillispie
1 0 The Laws of Motion, and Proposition One 74
Isaac Newton
82
1 2 Universal Gravitation 87
Richard P. Feynman, Robert B. Leighton, and Matthew Sands
91
95
VI
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
VII
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
Rogers.
"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
astonishment.
"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
in."
"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-
pensation."
"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
road.
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
himself.
"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-
tion.
"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
plate.
"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
though."
"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
this."
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-
dena.
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
said:
"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-
tech.
"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
10
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
Wilson.
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.
11
"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-
raphy."
"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
12
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
us."
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
time.
"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
system."
13
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
situation."
Sarth 3 A
There was a general murmur of assent, so Weichart went
on:
"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?"
Sarth
directum ofmotim of cloud
14
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
15
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,"
16
Opening Scenes
said Marlowe, putting out great volumes of smoke.*
"Yes, it seems unimpeachably correct," answered Wei-
chart.
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 D2 dt
_ Tr dD . da d Tr
But V = ' so that we can write — = — V.
dt dt D2
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
da
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
Aa
months."
17
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
notice.
"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-
pose?"
"Goodness, man, is it as serious as that? Wait a min-
ute."
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
18
Opening Scenes
procrastination and delay."
"You certainly would, like an old hen sitting on a bad
egg-"
"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
do?"
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
question.
"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-
ington.
"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."
19
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."
20
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-
atic."
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.
21
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
22
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.
23
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,
24
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
25
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"),
26
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
27
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 . . .
28
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
those.
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,
29
since Triton was a demigod of the sea and a son of Neptune
(Poseidon).
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
30
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
do.
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-
31
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.
32
33
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.
34
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
35
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
Palomar."
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
telescope.
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
36
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.
H
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
yard.
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
straight."
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."
So
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
37
38
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-
scope.
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."
A,
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
39
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-
where."
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.
K
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-
40
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!"
D,
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
now."
Just after midnight. Dr. Greenstein
came up from the darkroom. He
checked the star, which was ticking
41
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
midnight."
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."
A,
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.
42
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.
TO THE MOST HOLY LORD, POPE PAUL III.
THE PREFACE OF NICOLAUS COPERNICUS TO THE
BOOKS OF THE REVOLUTIONS
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
avoided.
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
43
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
investigations.
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
44
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.
45
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.
46
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.
ASTRONOMICAL MESSAGE
Which contains and explains recent observations
made with the aid of a new spyglass3
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.
47
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
made.
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.
48
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
attitude.
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
49
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 F2, F8> F4, etc.
50
Kepler's Celestial Music
Fig. 14. The Ptolemaic system (A) and the Copernican
system (B) were of about equal complexity, as can be
51
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 F2 and Ft,
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-
52
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
ellipse.
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-
tion.
53
Hyperbola
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
side.
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
54
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.
55
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:
Tetrahedron
Cube
Octahedron
Dodecahedron
Icosahedron
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
triangles.
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.
56
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
Cube
Sphere of Jupiter
Tetrahedron
Sphere of Mars
Dodecahedron
Sphere of Earth
Icosahedron
Sphere of Venus
Octahedron
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.
57
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
(1597).
58
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
wrote:
"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
puerilities."
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?
59
"1. Concerning the five regular solid figures.
2. On the kinship between them and the harmonic
ratios.
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
movements.
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
another.
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.
m
P^w* M|"
Saturn Jupiter
Mars
>f -gj T#g£l!ffffT
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!
60
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
physics.
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.
61
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.")
62
Kepler
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
communion).
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
63
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.
64
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-
sults.
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-
dence.
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.
65
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 Narratioof 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.
66
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
one.
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.
67
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-
68
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
69
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
70
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
away.
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.
71
"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:
72
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.
73
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.
A X I OM A TA,
SIVE
LEGES MOT US.
LEX I.
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.
74
The Laws of Motion, and Proposition One
LEX II.
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
componitur.
LEX III.
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.
75
COROLLARIUM I.
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.
PROPOSITIO I. THEOREMA I.
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
76
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.
77
AXIOMS, or
LAWS OF MOTION'
LAW I
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.
LAW II2
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.
LAW III
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
78
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
Scholium.
COROLLARY I
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.
79
SECTION II
The determination of centripetal forces.
PROPOSITION I. THEOREM I
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.
80
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.
81
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
82
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
83
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
ago.
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-
selves.
But it is more natural to suppose that life has
developed in the planets of our solar system, the
84
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
85
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.
86
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,
87
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.
180°
Fig. 7-7. Orbit of Sirius 8 with respect to Sirius A.
88
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.
89
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?
90
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
91
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 0 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
now.
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
92
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 0 (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
93
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
intelligently.
94
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
Analysis.
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
system.
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
95
time because of their unique nature,
their wide interest, and their obvious
relevance to the forthcoming Mariner
1971 (orbiter) and Viking 1973 (lander)
missions.
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
effects.
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. . . .
96
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
frames.
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.
97
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
Hellas
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-
minator.
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
scattering
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 . . . .
98
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
frames.
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,
12).
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
Mars.
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.
99
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.
100
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.
101
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
recognized.
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).
102
Mariners 6 and 7 Television Pictures; Preliminary Analysis
(a)
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 10G 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 10G-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
103
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
region.
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
MARINER 6
NEAR-ENCOUNTER
FRAMES 20 AND 22
~\ I I I l l l
MARINER 6
NEAR- ENCOUNTER
FRAMES 19 AND 21
a
'Ol I i i i I
2 3 4 S 6 8 10 20 30 40 60 100
CRATER DIAMETER (D).Km
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').
104
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
• ' .
?
.
Br
t
6N14 J
105
319° E
3.5<
mm
V:. •••::•) Y.:-\&V-
13.8*
6N7
342.4° E
0
■?h
• V
,~c<6N6".,7
M 6NI4 0
1/
i u.;
Q6N8"
0
o
O
NORTH
0
0
.s
o
-I0<
o
o
o
312° E
-24.7
0
1 1
100
1 , 1
300
i
500
I
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-
mosphere.
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.
106
Mariners
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
primordial.
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
108 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-
107
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.
108
Mariners
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-
position.
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 COL. 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 H20 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-
109
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
H20 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
110
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 C02 is the
same for Mars as for the earth, then,
from the mass of COL> 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
state.
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
planet.
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-
111
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
time.
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-
sits.
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
112
Mariners
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-
113
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
chosen.
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
resolution.
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 Hl.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
remnants.
114
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
(1965).
, "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
necessary.
. 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-
perature.
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-
ration.
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
(1927).
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.
115
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
article.
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
ILLUST.ATf 0 BT CO VOUNu
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
116
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
photographers;
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
117
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
stars."
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
118
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-
struments."
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
119
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-
couragement.
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
amateur."
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
brightening.
By February and early March, 1963, Comet Ikeya
120
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
skies.
121
The director of the Central Bureau for Astronomical
Telegrams describes the excitement generated by a
recent comet, and reviews current knowledge of
comets.
16 The Great Comet of 1965
Owen Gingerich
An article from The Atlantic Monthly, 1966.
a
"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
122
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-
123
Seki might die by fire, plunging directly into the
sun.
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 !
A,
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
124
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
comet.
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
Virginia."
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
comment:
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
indicates.
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
125
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
questions.
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
126
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."
127
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
128
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 1087 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
precision.
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
129
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
SI
Centrifugal forces
due to earth's
rotation
Gravitational forces
due to earth's mass
Accelerations of masses equal
9
to 3 parts in 10
Princeton Experiment
Gold
Centrifugal forces
due to earth's revolution
around Sun
I
Aluminum
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
130
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 10n, an improvement of two orders
of magnitude over Eotvos' original experimen-
tal precision of 3 parts in 109.
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 = Mc2) 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 1011 of the new Eotvos experiment, its
result says that — to within about 1.3 parts in
108 — 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
131
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-
actions.
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
nucleus.
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
itself.
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
months.
Feedback Circuit Feedback electrodes f"
5 k 4 V 0.5 /iF v ., . I
Aluminium
I
4-
r eeuuacr
IV 0.5 uF v
Optical-Lever Telescope
Bridge
Oscillator
Filter \j> DC output
Circuit "^
Lock-In ^ Reference!
Amplifier "^ input
132
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.
133
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
134
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
135
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
intolerable.
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
136
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
137
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
138
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
139
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
140
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 102, a million, 106; a
billion, 109 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 109 instead of $5,760,-
000,000.
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 10u-or written in full, 100,000,000,000. Our
present telescopes can observe something like 109 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 10u times 109 stars, or 1020 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— 106— numbers. The cosmic directory would be 1014
141
times bigger, to hold its 1020 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
planets.
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.
142
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.
143
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
I
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
144
Is There Intelligent Life Beyond the Earth?
N = RtfaefififcL
R* is the mean rate of star formation, averaged over the lifetime of the Galaxy; fp is
the fraction of stars with planetary systems; nc 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; fc 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 ~ 10n, most of which have
masses equal to or less than that of the Sun. The age of the Galaxy is ~ 1010 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 ne — 1 . However, the bulk of
the main sequence stars — well over 60 percent — are M stars; as we mentioned in
145
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 nc — 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
forth.
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
146
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~ 101.
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
147
after reaching the communicative phase (L less than 102 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 108 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 /,, fif and fr 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 fc.
V Our two choices for L — < 102 years, and >> 108 years — lead to two
values for N: less than ten communicative civilizations in the Galaxy; or many more
than 107. 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 — 107
years. This then yields as the average number of extant advanced technical
civilizations in the Galaxy
N ~ 106.
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
148
149
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.
150
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151
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.
INTRODUCTION
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
152
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
tasks.
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
153
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,
154
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
Michigan.
Dr. David M. Dennison, Professor of Physics, University of
Michigan.
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
University.
Dr. Mark Kac, mathematician, Professor at Rockefeller
University.
155
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
156
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
157
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
Investigation."
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
158
Scientific Study of Unidentified Flying Objects
possible, be such that any other scientist can confirm his
results.
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
impressions.
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
clues.
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
this.
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
159
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
standards.
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
160
Scientific Study of Unidentified Flying Objects
Section I
CONCLUSIONS AND RECOMMENDATIONS
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
161
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
long.
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.
162
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
flying.
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-
163
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
phenomena.
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
164
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
165
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.
166
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?
167
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
169
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
170
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
171
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
172
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
173
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
174
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.
175
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
life-history.
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
life-history.
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
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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
177
EO NGC 3379
E2 NGC 221 (M32)
E5 NGC 4621 (M59)
E7 NGC 3115
NGC 3034 (M82)
NGC 4449
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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.
179
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
stars.
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
180
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
181
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
182
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
183
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.
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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
185
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
187
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
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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
189
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
190
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
aged?)
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.
191
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
192
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
193
CLUSTER DISTANCE IN
NEBULA IN LIGHT-YEARS
RED-SHIFTS
:C«0N4 BC0E4LI'
600,000,000
800,000,000
1,400,000,000
2,200,000,000
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.
194
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
195
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
distances.
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.
196
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.
humcuuMyC
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.
ferret/
reootisrK,
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
197
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
198
Negative Mass
Quasi-stellar radio source 3C 273
u
motii
&
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
199
'oCoxLfc
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.
■HM/itomfr
•«
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
200
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.
FURTHER READING
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)
ACKNOWLEDGEMENTS:
Mount Wilson and Palomar Observatories (page 75, bottom, and page 76, top)
201
25 Four 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
from TROILUS AND CRESSIDA
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
202
Four Poetic Fragments About Astronomy
from HUDIBRAS
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
203
MY FATHER'S WATCH
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
204
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
205
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 1021 manlike beings — approximately 1014 more people than presently inhabit
the Earth.
206
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
10s 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 1019 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 1023
grams, while the amount of deuterium is approximately 5 x 1019 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 1038 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 10J4 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
207
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.
208
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 enr2 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
words,
209
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
techniques.
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.
210
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 103" gm, and the store of energy which would be released
from the conversion of this quantity of hydrogen into helium would be approxi-
mately 1049 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 1033 erg sec1, 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 1031 gm of solar hydrogen
—25 times more than the mass of Jupiter— would provide some 3 x 1050 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.
211
Authors and Artists
ISAAC ASIMOV
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
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
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
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
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
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
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
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.
212
HENRY S. F. COOPER, JR.
RICHARD PHILLIPS FEYNMAN
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.
COPERNICUS
See Unit 2 Text, Section 6.1
JEAN BAPTISTE CAMILLE COROT
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
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
astrophysics.
STEPHEN H. DOLE
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
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.
GALILEO GALILEI
See Unit 1, Section 2.2
CHARLES COULSTON GILLISPIE
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.
213
Authors and Artists
OWEN JAY GINGERICH
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
computer.
BANESH HOFFMANN
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
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
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
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.
JOHANNES KEPLER
See Unit 2 Text, Section 7.1.
PAUL KLEE
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
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.
214
RICHARD LIPPOLD
PETER GUY ROLL
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
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.
ISSAC NEWTON
See Unit 2 Text, Section 8.1-
PABLO RUIZ PICASSO
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
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
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
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.
215
Authors and Artists
I. S. SHKLOVSKII
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
Sciences.
JOSEPH WEBER
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.
WALTER S. SULLIVAN
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,
Connecticut.
216
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