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HANDBOOK OF THE H HAVENS

Dana K. Bailey, J.A.C.

CIRCUMPOLAR TRAILS. A small camera, focused with a magnifier, was placed
upon the ground and pointed at the North Star and its neighbors. In an hour's exposure, the
stars revealed the rotation of the earth by recording on the photographic plate a fraction
of the apparent daily circle of each. The group arrangement of the Little Dipper with the
Pole Star at the end of the handle has been indicated at the initial position and the trails
show its subsequent motion. This picture was made with a fine lens in the clear desert
air of southern Arizona, and the original negative shows the trails of forty stars within the
diurnal circle of Polaris. Anyone with even a box camera can make similar pictures.

HANDBOOK
OF THE HEAVENS

SPONSORED BY

The ? American *%Cuseum of D^atural History

Editors
HUBERT J. BERNHARD

Director of Publication^ ftihior Astronomy Club

DOROTHY A.

Assistant Curator of thf llaydfn Planetarium', Adviser, Junior Astronomy Club

HUGH S. RICE

Associate in Astronomy, American. Museum, Sctrtl'fiJ'ic Associate , Junior Astrono

WITH A * ORE WORD BY

PROFESSOR HARLOW SHAPLEY

l)irector t Harvard College Observatory

New York WHITTLESEY HOUSE London
MCGRAW-HILL BOOK COMPANY, INC.

SKCOM) PRINTING

PUBLISHED BY WHITTLESEY HOUSE
A division of the McGraw-Hill Book Company, Inc.

Printed in the United States of America by The Maple Pres\ Co., York, Pa.

To
DR. CLYDE FISHER

Curator of Astronomy
American Museum of Naturaf^History

in charge of
THE HAYDEN PLANETARIUM

CONTRIBUTORS

DANA BAILEY ROBERT MILLER

GIRARD BLOCK JAMES ROTHSCHILD

RUTH FLEISCHER DICK SCHIRLING

ROBERT FLEISCHER DOROTHY SCHOOF

ANNESTA FRIEDMAN VERA WOLFSON

Louis HEYNICK

ACKNOWLEDGMENTS

GRATEFUL acknowledgment is here made to the many people
who have taken part in the preparation of this book. First
thanks are due to the contributors, members of the Junior
Astronomy Club at the American Museum of Natural History,
whose genuine enthusiasm for their hobby of astronomy has
made the book possible.

We are indebted to Dr. Harlow Shapley for his unfailing
interest and encouragement, and especially thank our many
friends at the American Museum of Natural History.

To Dr. Charles S. Adams, Director of Mount Wilson Ob-
servatory, and to Dr. Otto Struve, Director of Yerkes Observa-
tory, we are indebted for the photographic illustrations.

The unique assistance rendered by Dean Guy Stanton
Ford, Mrs. Chauncy Cooke, and Miss Anne E. Rumpf is
gratefully acknowledged, as well as that of many others who
have aided greatly in this undertaking.

THE EDITORS.

AMERICAN MUSEUM OF NATURAL HISTORY,
September, i

FOREWORD

MY FIRST impulse in writing to the Junior Astronomers about
their Handbook of the Heavens is to greet them in behalf of the
profession and congratulate them on their unearthly interests.
But the second is to warn them not to take the science too
seriously. As an avocation, there is nothing more mind-cleans-
ing than astronomy; as a profession, it is a hard master.

The young student should first discover in himself a high
talent for mathematics or for making experiments, or the
possession of a constructive imagination, before he ventures to
change his interest in stars and planets, lenses and mirrors,
from a healthy hobby into a business. The amateur astron-
omer and the unprofessional student are blessed with freedom
from deadening responsibility; they answer only to the per-
sonal urge to do or to know. They can observe and read and
think of velocities, masses, distances, and durations that are
uncommon to the inhabitants of the earth's crust. They can
play, at least in thought, with meteors and galaxies which
are so different in size, so similar in origin, meaning, and
obedience to cosmic laws. In a life of petty turmoils, the
Junior Astronomer, by detaching himself from the earth, is
preparing for one of the highest enterprises in the realm of
contemplation the wholly impersonal Dream.

HARLOW SHAPLEY.

HARVARD COLLEGE OBSERVATORY,
CAMBRIDGE, MASS.,
September > 1935.

CONTENTS

FOREWORD, BY HARLOW SHAPLEY xi

LIST OF ILLUSTRATIONS xv

EXPLORING AMONG THE STARS 3

STARS OF THE NORTH POLAR SKIES 5

AUTUMN AND WINTER SKIES 12

SPRING AND SUMMER SKIES 22

STARS OF THE SOUTHERN SKIES 29

EXPLORING AMONG THE PLANETS 37

EXPLORING ON THE MOON 51

METEORS AND METEOR SHOWERS 60

COMETS 65

DOUBLE STARS 69

SOLAR OBSERVATIONS 74

NEBULAE AND CLUSTERS 80

VARIABLE STARS 88

HINTS ON TELESCOPE USAGE 94

ASTEROID HUNTING 101

AMATEUR ASTRONOMICAL PHOTOGRAPHY 109

OBSERVATIONAL SCRAPBOOK 115

GLOSSARY 121

INDEX 125

xvi List of Illustrations

Mare Imbrium Region of Moon 58

Chart of the Moon 59

Meteor Trail 61

Meteor Radiant 61

Halley's Comet 67

Comet Debris 67

Binary System 71

Double Star Kriiger 60 73

Sun's Disc 77

Solar Eclipse , 77

Great Nebula in Orion 81

Ring Nebula in Lyra 81

Great Nebula in Andromeda 82

Horsehead Nebula in Orion 82

Mosaic of the Milky Way. . . . . 83

Star Cluster in Hercules. ... . . 84

Double Cluster in Perseus 84

Light curve of Delta Cephei 91

Refracting Telescope, Equatorial Mount 95

Chart of the Asteroid Vesta 107

Chart of the Asteroid Juno . . . . 108

Orion, an Amateur Photograph ....in

Venus and the Moon in

The Moon, an Amateur Photograph 113

Ahnighito Meteorite 117

Celestial Coordinates . 118

In addition, there are 32 charts and diagrams which appear in the text
but which are not listed here.

HANDBOOK OF THE HEAVENS

Exploring among the Stars

IT is fun to watch the stars and to make friends with them
to see the Big Dipper and to know that by this star picture
Greek shepherds told the hour of the night, American Indians
timed the planting of their crops, and Columbus guided his
boat to a new world.

Memories of the rough-hewn men who first looked to these
stars for guidance and companionship return to us. And they
conflict with thoughts of civilizations which will rise and fall
under these same stars. That is the romance of the skies.

Just as the bird lover rejoices to hear the notes of the first
robin in the spring and the gardener smiles to see the early
crocus pushing through the wintry soil, so those who have
discovered companionship in the stars welcome the return of
old favorites to the skies. Each hour of the night and each
season of the year new stars come into view.

Exploring on one's own, one finds among the star groups
or constellations imaginary pictures outlined by the stars.
Some are so ancient that they are found on Babylonian stones;
others so modern they include an air pump. Perhaps the
best known of the constellations are the zodiacal groups which
form a backdrop of stars along the path which the sun, moon,
and planets always seem to follow. In this historic region of
the sky three new planets have been discovered by the watch-
ful eyes of astronomers. There shines Venus, a blaze of glory
in the morning or evening sky; and in the same path ringed
Saturn creeps, spending two years in one constellation. The
moon, too, wends its way among the animals of the zodiac.

In one night of watching the stars we may become familiar
with many of them. We may learn to know many of the
constellations at sight. But then we have learned only the
stars visible at that time. There are hundreds more. Later
in the month or even later that same evening new stars will

4 Handbook of the Heavens

have risen above the horizon. In one night we may see several
planets. But there are others. In one night we may find fifty
markings on the surface of the moon. But there are thousands.

So all the nights of a lifetime are not enough to discover
even half the secrets of the skies. We can learn only a few;
always there remains something new, something unknown to
lure us on. Perhaps some one of us may find something that
has never been noticed before !

It may be this book will reveal to you the fascination of the
stars. To that end it is written.

Stars of the North Polar Skies

DAILY swinging around the north celestial pole, never setting
for observers in the latitudes of New York, are the keystones
of constellation study, the circumpolar stars. Forming an easy
guide to the location of other groups, they are in themselves
of extreme interest.

Most easily recognized and most important of all these
constellations is the Big Dipper. Ursa Major, as it is known to
astronomers, means Greater Bear, but no name could suit this
group better than the "Dipper" for it looks exactly like one.

6 Handbook of the Heavens

Four stars form the bowl and three the handle; and the
resemblance is the more perfect since all but one of the stars
are of the same magnitude.

In this dipper the second star from the end of the handle
is an object that carries us back to the days of the early
Arabs. This is the star Mizar and its faint companion Alcor
which form a naked-eye double. So difficult is it to see Alcor
that this was the standard eyesight test given to recruits for
the Arabian army. **

Although to the casual observer the bowl of the dipper
may seem almost devoid of stars, a careful count with the
naked eye on a clear night will reveal ten or twelve faint
ones. In this area are located several famous telescopic
objects.

It is with the use of the Big Dipper, more widely known
than any other group, that the Pole Star is found. By following
a line drawn through the pointers of the bowl (the two stars
directly opposite the handle), and continuing through the top
of it one comes to Polaris, the North Star, guide of mariners
for untold generations.

Polaris, which is about twice the moon's apparent diameter
from the true north celestial pole, does not stand alone in the
sky; instead it is the brightest star of the Little Dipper, or
Ursa Minor. This group is more difficult to make out than is
its larger brother, for the stars are fainter and of varying
degrees of brightness. Two, which occupy a position in the
bowl similar to that of the pointers in the larger constellation,
are fairly bright and are easily found on a clear night. They
lie between the pole and Draco, and because they seem ever
to be on guard against an attack by the dragon upon Polaris,
they are known as the guardians of the pole.

Draco itself starts in a rather faint star which is slightly
nearer to the pointers than to Polaris and winds its serpentine
length in a rough half circle around the Pole Star. Then, at a
sharp angle to its former path, it rears its head, marked by a
pair of prominent stars which might be taken for eyes, at
Hercules. The Dragon provides a not-too-difficult group to

Stars of the North Polar Skies 7

hunt for and one which, as it gradually unwinds to the be-
ginner, becomes more and more interesting.

Polaris now is the North Star, but it was not always so.
Owing to a "wobbling" of the earth's axis the north pole of
the sky is constantly changing its position with respect to the
constellations. Thousands of years ago Alpha Draconis, one
of the dimmer stars in Draco, was the Pole Star, and at some
date far in the future the bright star Vega, which now shines
in the summer skies, Will be near the pole.

Across the pole from Ursa Major, and equally distant from
Polaris, lies a group of stars that resembles a big chair. This is
Cassiopeia, better known as the Seated Lady. Its startling
resemblance to a W is enhanced by the fact that nearly all
the component stars are approximately of the same brilliance.

Cassiopeia, like all the constellations, is more than an
outline of bright stars visible to the naked eye. It encompasses
a sky area in which are numerous stars of various degrees of
brilliance. All the stars are classified according to their bright-
ness and grouped in magnitudes. A star of the first magnitude
is 2^2 times brighter than one of the second magnitude, and
this proportion is used throughout the scale. Stars brighter
than first magnitude a?e reckoned below zero, given propor-
tional negative values, and designated by a minus sign. Thus
the highest number represents the least brilliance and Sirius,
our brightest star, is 1.58. At the other extreme are the faint
sixth-magnitude stars beyond which the unaided eye cannot
see.

Telescopes have revealed objects down to the twenty-first
magnitude and they have also revealed in many cases two or
more stars where only one was visible to the unaided eye.
Such a double star is Eta (77) Cassiopeiae, so called after the
common practice of using Greek ' letters to designate the
different stars in the constellations. Even stars so well known
as to have proper names of their own are also given Greek-
letter designations; thus Sirius is Alpha (a) Canis Majoris.

Perseus is interesting because it is the radiant point for
the August meteor shower that bombards the earth with

8 Handbook of the Heavens

countless shooting stars each year. It is only partly circumpolar
for these latitudes, for here a greater part of it dips below the
horizon for a short time every day. To be entirely circumpolar
an object must have a polar distance that is less than the
observer's latitude. Wherever one is on the earth's surface,
his celestial pole is as far above the horizon as his latitude.
Thus a person in the latitude of New York, 41, would
count circumpolar all stars within 41 of the north celestial
pole.

Perseus contains two stars which vary in brightness within
the limits of naked-eye observation. One is Rho (p) Persei,
which ranges through a whole magnitude in about a month, and
the other is Beta (/?), the famous Algol, or Demon Star, which
changes as much in a few days.

Between Perseus and Cassiopeia lies one of the most
interesting objects for amateur observation found within the
circump6lar boundaries. This is the double star cluster Chi-h
(x-h) Persei. Faintly visible to the naked eye under good
conditions, it becomes an object of beauty when seen through
an opera glass.

Two other less prominent constellations fall into the cir-
cumpolar group, Cepheus and Camelopardalis. Cepheus may
be located by continuing the line from the pointers of Ursa
Major through the Pole Star and extending it on for about
once again its own length. This will take the beginner to a
previously unexplored sky region, and in it he will find a rude
lantern composed of third- and fourth-magnitude stars.
The Milky Way runs through Cepheus, and in the constella-
tion are found several interesting double stars. Among these
is Delta (5), which is not only a yellow-and-blue double but
also a famous variable star after which the Cepheid type
of variable was named.

Lacerta, Lynx, and Camelopardalis are real challenges
to the sky explorer, for they are all composed of exceedingly
faint stars which are not arranged in any striking formations.
In an effort to build Camelopardalis up from nothing, locate
Alpha and Beta, and from these, with the aid of the connecting

Stars of the North Polar Skies 9

lines on the charts, the rest of the stars can be found. But even
this elusive group can be observed on any very clear moonless
night during the year and so it should soon become as well
known as its more prominent neighbors.

Stars of the Autumn and Winter Skies

The map above shows positions and accepted geometric patterns for all the constel-
lations visible at 9 P.M. November I in latitude 40 north. Identification of the star groups
may be made by comparison with the chart on the opposite page.

In use, this map should be held overhead and oriented according to the compass points
indicated. It will then show the stars as they appear in the sky. The stars visible here at
9 P.M. November I will also be visible at 7 P.M. December I and at n P.M. October i as
explained in the chapter on "Autumn and Winter Skies."

Chart of Autumn and Winter Skies

Urse* Major

< V-4-* ^N

jorV'''' >..-

Lynx

1 J i u*mej<*par/*fohs .

I Gefnini r"\a /Q \*'Y \"7^ L

^ / ^ ^ ! v: V u3

* /I ^.^W *'-~*''^. ** '' m IA

Aur \6ifc* t"f" ml--* tf^

{ r ,/ J ,/ . Nr

\ ,/ PbCTrf. 6" Drflc ^!7 ,.- v "^>-

. ot'''../.. -^ ^ Hercules.-

a /

Taurus

% ^.

Delphinus

v Tec ' ueipnn

Aries; r-*55 .' Pegasus ^

<^-\ / -^^ / <>

Erid^nu^ \Cctus

-,> x:\

.V r --v

Forn^ix

Sculptor Piscis V>

^ * N Aus+rin r '

The map above shows the accepted geometrical patterns of all the constellations visible
at 9 P.M. November I in latitude 40 north. All the stars listed for study in the chapters on
"Double Stars" and "Variable Stars" are indicated, as are the first-magnitude stars, which
are the following:

a Geminorum Castor a Tauri Aldebaran a Aquilae Altair

ft Geminorum Pollux a Lyrae Vega a Piscis Austrini Fomalhaut

a Orionis Betelgeuse a Cygni Deneb a Aurigae Capella

Autumn and Winter Skies

DURING the cold winter months the display of brilliant stars
dotting the night skies is at its best. But really to learn
the winter constellations one must start in autumn and
continue on into the season of snow and ice, thereby gaining
an understanding of the transitions that take place in the
heavens.

Early in the evening, just around the time that autumn is
officially ushered in, we find the impressive Northern Cross,
embodied in the constellation of Cygnus, directly overhead.
With its first-magnitude star Deneb, the Cross is easily traced
among the stars, and at its base is found the beautiful double
star Albkeo.

Near Cygnus is the small constellation Lyra, which con-
tains within its borders the blue-white star Vega. Both Vega
and Deneb will be setting in the west later in the evening at
this time of the year, for they belong with the summer stars.
The brightest of the summer stars, Vega, as it sets will be
superseded by the even more brilliant Sirius, rising in the east.

Aquila, the Flying Eagle, is southwest of Cygnus and in
it there is the first-magnitude star Altair. This is a white
star, and it may be distinguished in that it makes a triangle
with Vega and Deneb.

Northeast of Aquila is a small and not so important con-
stellation, Delphinus, the Dolphin, or Job's Coffin. In this
is a cluster which is estimated to be 220,000 light years away
one of the most distant objects known until recently. The
limit of visibility now extends 2,000 times this distance and
objects may be photographed which are 500 million light years
away.

Somewhere about halfway between Cygnus and the eastern
horizon a great square of bright stars fills the sky. This is
Pegasus, the Winged Horse, and the area within the boundaries

dutumn and Winter Skies

DELPHINUS

V CYGNUS

x > V \ Ring Nebula.^ LYRA
,/AQUllA*

-M3.

ARIES/

/ PISCES
/ >--~"~-.,

PEGASUS
^ j

of the square presents a challenge to the observer. Under
ordinary conditions only a small number of stars can be seen,
but under ideal conditions as many as eighty have been
identified with the naked eye.

Extending from the northeast corner of Pegasus is part of
Andromeda, which contains the only spiral nebula in the whole
sky visible to the naked eye. The nebula is marked M 31
in the accompanying diagram. Between Andromeda and the
horizon is a little triangular group of fainter stars appropriately
named Triangulum. Directly south of Triangulum lies Aries,
the first zodiacal constellation.

Looking along the zodiac to the west of Aries, we find the
stars of Pisces. The rather faint stars are difficult to identify
but the constellation is an important sky mark, for in it is
located the vernal equinox, a reference point for the positions
of all celestial objects.

Somewhat toward the south and coming up on the eastern
horizon is Cetus, the Whale. In this larger group is found the
famous variable star Mira which is at times as bright as Polaris,
then fades to the limit of naked-eye visibility, and finally drops
from view except in a telescope. Stars of this type, which vary
in brightness, are discussed more fully on page 88.

The Pleiades, in Taurus, the Bull, consist of seven stars,
almost universally known. To the Babylonians they were
"the many little ones"; to the Greeks, "the seven sisters";
to the American Indian "the seven brothers"; and so on.
Actually, there are about 250 stars in the cluster, but even on a
very clear night only seven can be distinguished without optical

Handbook of the Heavens

CETUS

ERIDANUS'

,-*-*v /

f **

aid. Sometimes it is hard even to see the seventh star, which
is called the "lost" sister.

The month of November is known as the Pleiad month
because the Pleiades are prominent in the eastern sky early
during the evening. Later the same evening the stars will
climb toward the south, reach their highest point, and sink
in the west, retracing the path laid by the sun twelve, hours
before. The westward motions of sun and stars are apparent;
the true motion is that of the earth as it turns eastward on its
axis every twenty-four hours. Thus new objects are coming
into view on the eastern horizon all night long.

The rising and setting of the stars are also affected by the
earth's yearly revolution around the sun. As a result, in every
two hours of watching on any night observers may see objects
visible one month later during the two preceding hours. For
example, a person observing between the hours of 10 and
midnight on July 4 will see the stars visible from 8 to 10 on
August 4. Similarly, on any morning from 3 to 6 A.M. one can
see the evening stars of the coming season.

Another group of stars found in Taurus is the Hyades
almost as well known as the Pleiades. This is a V-shaped cluster
with the first-magnitude star Aldebaran at the lower end.
Aldebaran is a fiery-red star visible for eight months of the
year. It is frequently obscured from our view by the passage
of the moon between it and the earth. This occultation, as
such a happening is called, is striking to watch.

Fomalhaut moves across the southern evening sky during
the autumn months, but when winter begins it is no longer

Autumn and Winter Skies

Be+clgeuze mf*

- \ i Bi ..-.::;.-^ .<_ /

Procyon / / "" f "/^

A y ^MO^OCEROS ij

{ " /; y v r "T Sinus

: /*t637 CANIS MAJOR^

t -f.V" *

> /-? 4><

visible. It is the brightest star in Piscis Austrinus, a constella-
tion composed of faint stars. This group can hardly be traced
in outline from these latitudes, although Fomalhaut is of the
first magnitude and is a conspicuous sky mark.

One of the most striking of the constellations, Orion, lies
just below the horizon, soon to reveal itself. Toward the end
of October it can be seen rising at 9 o'clock. As it comes into
view, the groups of Hercules and Ophiuchus are sinking in
the west, and Fomalhaut has traveled two-thirds of the way
across the southern sky.

Betelgeuse forms the right shoulder of Orion and is one
of the few stars mentioned by name in the Bible. Bellatrix,
neither so well known nor so bright, forms the left shoulder,
while Rigel, blue-white and a star of the first magnitude,
lies at the left foot of the hunter or warrior depicted by the
group.

Orion can easily be found in the sky by looking for three
stars, all of the second magnitude and in a straight line, which
make up the belt. In the sword attached to this belt is a
beautiful nebula, one of the two in the northern skies that can
be seen without optical aid. Of the three objects in the sword,
it is the central one, Theta (0) Orionis.

Almost squarely beneath Orion's feet is little Lepus, the
Hare; and Eridanus, the River, also has its source in this
region. Beginning at the blue-white star Rigel, it passes below
Taurus and winds beneath Cetus, the Whale. No very con-
spicuous stars mark these two constellations but they are
interesting to find, as is near-by Columba.

Handbook of the Heavens

Castor

GEMINI
M35

CACER \

M37^ H 38 '' 1 '
^-_ AuKlGA ^

r o^ T ' ER'lDANUS

o^Rigel in ORION

the great ship Argo Navis, which has been split up into several
sections, of which Puppis is the most prominent to be seen
from our latitude.

Cancer, the Crab, is the next zodiacal constellation to
come up over the horizon after Gemini, and in it is the famous
Bee Hive cluster, Praesepe, which is visible to the naked eye.
A diagram of Cancer with the location of Praesepe appears
on page 16. A zodiacal group, Cancer acts as host to many
of the planets and the moon.

Almost overhead at 9 o'clock on early February evenings
is Auriga, the Charioteer. With its extremely bright yellow
Capella it is easy to locate. This group, rich in clusters, is
right in the middle of the Milky Way. It narrowly missed
being circumpolar and has some stars within the boundaries
of the circumpolar groups.

Stars of the Spring Skies

The map above shows positions and accepted geometric patterns for all the constel-
lations visible at 9 P.M. March I in latitude 40 north. Identification of the star groups may
be made by comparison with the chart on the opposite page.

In use, this map should be held overhead and oriented according to the compass points
indicated. It will then show the stars as they appear in the sky. The stars visible here at
9 P.M. March I will also be visible at 7 P.M. April I and at 11 P.M. February i.

Chart of the Spring Skies

r* N

Lacerta

?<^~

/'-A \ A^V""

f \E/ y ^

i -.., " rvCephcus

1 1-4^. //* .

D C t Ursa Minor ^ ^ a

D^UK.'C TV

UrsoT^. Major

Ancfrome0

Polaris ^ j '' X

Cassiopeia 7*'Trian0ulum

< V^l^il9 VtllMIILI . ~

Coma* * Berenices

L/nx

"**

; Leo Mi nor
\ u:L * :: / jr-1

1 N^:-- v

V.* f j

Aries

Vi T . ".r L \* '-^/r "^"'nini

;- -f-*.,/ - T *\ ^nccr f X

\ * Canis X A% * . ^ tridyius

\ ^ **-fr Minor^''^""'" \*I\ ^ r ''

\ ^ Corvus *-*! <.' jf \ js>p /

\"^ *L_ Qovf/nrie T ** _,^t=--___ _ *.4Si . /

Pyxis '^ ; /Puppis

...XV Szr -V V'Orion
Mondceros
*

The map above shows the accepted geometrical patterns of all the constellations visible
at 9 P.M. March i in latitude 40 north. All the stars listed for study in the chapters on
"Double Stars" and "Variable Stars" are indicated, as are the first-magnitude stars, which
are the following:

a Aurigae Capella a Geminorum Castor

a Leonis Regulus /3 Geminorum Pollux

a Tauri Aldebaran a Orionis Betelgeuse

/3 Orionis Rigel

a Canis Majoris Sirius

a Canis Minoris Procvon

Stars of the Summer Skies

The map above shows positions and accepted geometric patterns for all the constel-
lations visible at 9 P.M. July I in latitude 40 north. Identification of the star groups may be
made by comparison with the chart on the opposite page.

In use, this map should be held overhead and oriented according to the compass points
indicated. It will then show the stars as they appear in the sky. The stars visible here at
9 P.M. July I will also be visible at 7 P.M. August i and at 1 1 P.M. June i.

Chart of the Summer Skies

s ^Andromeda
'/ ?A*

V,*"** N

terseusX ~* \ a" H -^*N
n/ 1 f ^ Auriga

* * *

.^ Cassiopeia '* Camelopardalis % ^ v

Pegasus

/ -4 * &' V ' * Ly \

//" fl \ *~'^ Vpheus ; Ursa Minor
/ \*Lacerta _ V - ?-f,

Cygnus f

fft *'* f' I ? Ur$a Major

Draro /'' .^ i"*^ /

y rf

Eciuuleus " s.VSagitta I u l> * iw v '^ Coma ^Berenices W

* a t- * *%'' '' ^3 N ? s>% * T *

/Aquarius ^ i ~* Herculesj \ Corona V-^ \

"' ^ >A ., L * ^iSL^e ^ /

lAquila ^ *tt <4 ^Dootes -^ ^

x ^(JJ L /) 4 ""^ *L /I

K Capricornus S ', \ r r\/"C"*T"* /

V ^X \ Ophiuchus\ : Virgo /

\ v.^ \ \ > 4 * /, S /X Corvus I .'

nfttarius

/ Scorpio

The map above shows the accepted geometrical patterns of all the constellations visible
at 9 P.M. July i in latitude 40 north. All the stars listed for study in the chapters on
"Double Stars" and "Variable Stars" are indicated, as are the first-magnitude stars, which
are the following:

a Aurigae Capella a Aquilae Altair a. Bootis Arcturus

a Cygni Deneb a Leonis Regulus a Virginis Spica

a Lyrae Vega Scorpii An tares

Spring and Summer Skies

AN ever-changing vista of constellations moves across the
darkened night skies as the earth pursues its yearly course
around the sun. From Orion, setting in the western sky in
the early evening on May i, around again to Orion rising
in the east on November i, an amazing display of objects
outlined in the stars is revealed to the eye.

Let us look at the heavens on an evening early in spring
at about 9 o'clock. In the west Orion is about to set, and Sirius
will also be sinking in the southwest, while Perseus and
Cassiopeia are in the northwest. Auriga, Taurus, Gemini,
Canis Major, and Canis Minor, all among the autumn-winter
stars, still stud the western half of the heavens.

Turning from these groups toward the south, and looking
up at a point nearly overhead, we see Leo, the brilliant Lion.
Worshiped by the ancient Egyptians because the sun entered
it about the time of the inundations of the Nile, Leo is one
of the oldest of constellations. Regulus, the Little King,
brightest star in the group, has a history of its own since it
w#s by measurements of the longitude of this star that,
thousands of years ago, the precession of the equinoxes was
discovered. Eleven times as bright as the sun, Regulus is a
double star but its eighth-magnitude component is unfortu-
nately not easy to observe with a small telescope.

Gamma (7) Leonis, second brightest star in the Sickle of
Leo, is one of the finest double stars in the sky. Although it
cannot be seen with a field glass, it can be resolved in a 3-inch
telescope on clear nights. The colors are yellow and green.

The Leonid meteor shower appears to emanate from this
constellation, radiating from a point within the sickle. The
planet Neptune, moving through the zodiac, has been in Leo
for a number of years and it is gradually working its way
eastward.

Spring and Summer Skies

LEO MINOR

Dtneboi" LEO > "7.. ,'fl\ L iBRA

4(X o ' _'' P N xL- 1 OKA

Regulus
T

t -..VIRGO \

Following Leo across the heavens is Spica, the brightest
star in the constellation of Virgo. A large and perfectly shaped
Diamond of Virgo is formed in the sky by the stars Spica,
Denebola, Cor Caroli, and Arcturus. Big though it is, Virgo
contains few brilliant stars, and its chief interest is to the
telescopist who can find in it many nebulae. Since the group
is one of the zodiacal constellations, it contains within its
borders at various times all the planets, the moon, and the sun.

Marked by the blazing Arcturus, Bootes is located a short
distance northeast of Virgo. It is surrounded by the stars of
Corona to the east and Canes Venatici and Coma Berenices
to the west. Although its shape suggests a giant kite, Bootes is
supposed, in mythology, to represent a farmer behind his plow.
Arcturus is the giant yellow sun whose light was used to open
the 1933 World's Fair at Chicago.

The constellation Canes Venatici, a misty patch of stars
located beneath the handle of the Big Dipper, is known as
the Hunting Dogs in mythology. Cor Caroli, third-magnitude
and the brightest star in the group, is an interesting object in a
small glass. It is a double with a sixth-magnitude companion.

A little group of faint stars romantically named "Berenice's
Hair" (Coma Berenices) can be found between Leo and
Arcturus. Only five or six of the group are visible to the naked
eye and they fail to form any easily recognizable pattern.
The number of stars in the constellation takes a startling jump,
however, when the region is viewed with a field glass which
will show from twenty to thirty stars, including several
doubles.

Handbook of ihe Heavens

J
/

o AJcor a

^ f $ r

\^U* ' B J 6TES \
U.VA CORONA% XX X H \

*' ' Z * r URSA MAJOR
Cor enroll

?<* / \ *** %XN ' N

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T w '' (v

CANES VENATICI

HERCULES V^ ^ j'

a l

COMA, V ^ : BERENICES

Stretching over a long distance south of Cancer, Leo, and
Virgo, lies Hydra with a pentagon of five faint stars marking
its head. Although it twists its way southeast among the
constellations for a distance equal to one-third the way
around the sky, Hydra presents only one bright star to the
observer. This is Alphard, a reddish star of second magnitude,
which is known both as the Solitary One and as Cor Hydrae,
the Heart of the Serpent.

Rivaling in dimness the stars of the Serpent, upon whose
back it rests, is the four-star group of Sextans which is so small
as to be overlooked. It represents for it is of modern origin
a scientific instrument, the sextant. Farther back from the
head of Hydra, nearly southeast of Regulus, lies Crater,
another small and inconspicuous constellation. Because of
the fact that its most brilliant star is only of the fourth magni-
tude, this little group is best observed on a dark, moonless
night.

A group closely associated with Crater is Corvus, the Crow,
which is near the tail of Hydra. Its stars are somewhat brighter
than are those of the groups with which it is identified, and
it is arranged in an eye-catching quadrilateral. Delta Corvi
is a pretty yellow-and-purple double.

Corona, the Northern Crown, is a small circlet of stars
located close beside Bootes. Despite the fact that with the
sole exception of Alpha it is composed of fourth-magnitude
stars, this little group presents an unusual and striking appear-
ance, similar in a way to a horseshoe, and most people find that
having seen it once they look for it continually.

Spring and Summer Skies 25

N ^'' SEXTANS

CORVUS

% 4 ""^

N..^ % ,5^ *> ^ : CRATER

HYDRA^ V X *..4 ^-f > ^ k a.^

\ \ / "- ^

...-"

If you should be observing in the middle of July, a great
change would greet your eyes. Looking west, you could recog-
nize Spica, Arcturus, Corona, and the Big Dipper, but in the
east would be a set of entirely strange constellations.

Vega, most striking of all the newly risen stars, would
almost certainly be the first to catch your eye. Surpassed in
brightness only by Sirius which rises later in the year, this
beautiful blue-white star will be about two-thirds of the
way toward the zenith, or overhead point. It marks the
approximate point on the celestial sphere toward which the sun,
together with the solar system, is speeding at a rate of 12^
miles a second.

A small and faint parallelogram of stars combines with
Vega to form the constellation of Lyra. Although they are few,
these stars are packed with interest. Epsilon (c), a naked-eye
double to very good eyes, is a quadruple in the telescope;
Beta's fluctuations in brightness are visible to the unaided
eye; and Delta and Zeta (f) are also doubles. Zeta is magnifi-
cent in low-powered instruments and Beta, in addition to its
variability, becomes a quadruple star when seen with a
telescope.

Set in the luminous Milky Way, Aquila, the Eagle, is
at this time about halfway between the horizon and Vega.
Altair, its brightest star, forms a triangle with Vega and
Deneb, of Cygnus, which also lies in the Milky Way. Cygnus,
the Swan, is more widely known as the Northern Cross, with
Deneb marking the top of the cross and the famous double
Albireo the bottom. Glorious star fields pervade this region.

Handbook of the Heavens

^ SERPENS)

; % "\
SERPENS I
Q^JCcxuda \

* \ OPHIUCHUS j
\ \ v /

r; \ \ X

v N ^ >'

SCUTUM V V

r/ CEPHEUS l-t f

'CASSIOPEIA 1 '^- , DRACO

LACERTA / , CY6NUS'

Between Corona and Lyra is the constellation of Hercules.
It necessitates gymnastics, but if, when the group is due south,
you turn toward the south and then bend your head 'way back,
you will see Hercules as the ancients saw him, kneeling with
one hand upraised. The group contains the wonderful cluster
M 13.

Covering a large portion of the space between Hercules and
the southern horizon is an immense pentagon of fairly promi-
nent stars which form the constellation Ophiuchus. The group
represents a physician who is holding a serpent, the constella-
tion of Serpens, in his hands.

Ophiuchus just borders on the Milky Way, which may be
seen on a clear, moonless night. Starting at its northern end,
we find Cassiopeia, and somewhat farther to the south is
Cygnus.

Between these two groups is a small house-shaped affair
with the top of the house pointing to the pole. This is Cepheus,
which contains Mu (ju), the fifth-magnitude Garnet Star,
famous for its deep-red color. It makes a startling contrast
with the white Alpha Cephei. Delta Cephei is a most interest-
ing type of variable, the first of its kind to be studied. Also
in this group is one of the "coalsack" or dark nebulae which
are found along the Milky Way. Beyond Cygnus the Milky
Way divides into two branches, one going through Sagittarius
and the other through parts of Scorpio.

As this striking constellation Scorpio climbs to its greatest
height above the southern horizon, its- bright-red star passes
the meridian. That bright-red star is Antares, the largest

Spring and Summer Skies

v --,,

Piscis CAPR1C RNUS

AUSTRINUS

SAGITTARIUS

r*>" \ o> Anto.res !

*"' K-^" A

C S SCORPIO

star known, and although it stays close to the horizon now it
will, because of the precession of the equinoxes, in a few
thousand years climb high into the heavens for these latitudes.

To the east of Scorpio is another important summer group,
Sagittarius, the Archer. It boasts no first-magnitude stars,
but it lies in the Milky Way with the Scorpion, and both groups
therefore contain much telescopic material. They are also
distinguished by the fact that both are zodiacal constellations.

Lying along the path of the ecliptic between Scorpio and
Virgo is the group of stars called Libra, the Scales. They are
supposed to represent the Scales of Justice, and the name also
bears some relation to the fact that when the sun is in this
portion of the sky the days and nights are of equal length.
Of the four bright stars here, two are interesting. Beta has a
greenish color unique among naked-eye stars and Alpha is a
field-glass double.

On the opposite side of Scorpio and Sagittarius, and also
in the zodiac, are Capricornus, the Sea Goat, and Aquarius,
the Water Bearer. Both are easily found with the aid of the
star maps published here. The faint stars of Capricornus
cannot be seen except in a clear sky because they are too dim
to penetrate haze and are easily blotted out by the glare of
street lights. An occasional passing planet serves to mark the
location of this butterfly-shaped group.

Near the end of August, Fomalhaut, first-magnitude star
in Piscis Austrinus, and the southernmost first-magnitude
star visible from New York, rises above the horizon. It never
climbs high, nor does it remain visible for more than a few

28 Handbook of the Heavens

hours at best, so it must be looked for at the proper time lest
it be missed.

In July, late in the evening, Pegasus and Andromeda, two
constellations considered as sure harbingers of falling leaves
and autumn winds, are beginning to rise. And when, right
below Andromeda, Triangulum and Aries come into view,
we know that autumn is actually at hand, bringing with it
new star groups.

Stars of the Southern Skies

SOUTH of the equator, where the constellation of Orion depicts
a man standing on his head, there are dozens of star groups
that cannot be seen by observers in northern latitudes.

But in the most southerly parts of the United States, the
Southern Cross (Crux) rises above the horizon for a short
time, and Canopus, the second brightest star in the heavens,
is visible, shining with a peculiar intensity.

The Southern Cross is preeminent. To persons below the
equator it takes the place of Ursa Major and provides a
celestial timepiece, reaching its highest southern point on
the meridian at 9 P.M. on May 15, when it is almost perfectly
erect, leaning very slightly to the east.

Crux is clearly outlined by four stars of almost equal
brilliance, and its likeness to a cross, therefore, is much more
distinct than is that of its northern counterpart. Gamma is
at the top of the cross, Alpha at the foot; Beta and Delta form
the arms. No star marks the intersection of the arms although
within the boundaries of the constellation there are about
thirty-two stars visible to the naked eye.

Its beautiful ruddy hue makes Gamma striking to the
eye but negligible on an ordinary photographic plate. Because
of its color it does not photograph well except on red-sensitive
plates, and this is the reason for the usual disappointment
people experience when examining pictures of the Southern
Cross. Kappa (K) Crucis, also deep red, is in the midst of a
fine cluster of about 130 stars, which are tinted in practically
all the colors of the rainbow.

A very interesting feature of the Cross is a coalsack nebula
which is situated just due east of Alpha and covers a sizable
constellation area. It is known as the Black Magellanic Cloud
and is in that part of the Milky Way which runs through

the Cross.

Stars of the Southern Skies

The map above shows the positions and accepted patterns for the constellations within
50 of the south celestial pole. Identification of the star groups may be made by comparison
with the chart on the opposite page.

Chart of the Southern Skies

O
63

lN \ 4 '' X / / > tf

2 >V ; South A*

;> .r < Celestial Pole< / ^.

j- \ t(^i /

TS ^ \ Mcns^f .

n ~ s& *--"" " A . / *^..

* t- r

% *

:i < \ . v >'

V^ ^^'4. ,/ ,#
->- \ ..-''-' I// '

N> , \^ * J

^ \ \^ D,VJ-^ : ~<

1 C ^m

1 ~ -e

Pictor | ^-

The map above shows the accepted geometrical patterns for the constellations within
50 of the south celestial pole. All the stars listed for study in that chapter are indicated, as
well as the first-magnitude stars, which are:
a Carinae Canopus /3 Centauri

CL Eridani Achernar a Crucis

a Centauri Crucis

Handbook of the Heavens

f V

VOLANS

,A*

f* \

VELA\

,5
47 S L HYDRU5 .*, .f Dor M

JOUCAN .^.V/.^"""*""* ; ' : '-V :? ;. vi
*"*^ .;'.; /'LESSER ' '''' ' ' ' /l\

Achern^r

.. ,

f "V Magellan ic,' ;
! V^ud I ;

x ^\ 4 /

RETICULUM* '/

DORAQUS

Drawing a line from Delta and extending it through Beta
Crucis, one encounters Beta and Alpha Centauri. Centaurus,
the Centaur, is one of the largest constellations in the southern
sky, measuring in length about 45 or half the distance from
the horizon to the overhead point, the zenith.

The two brightest stars in Crux are the second and fourth
brightest stars in the southern sky. Alpha Centauri, one of
the mdst widely known stars in the whole heavens, is the
third brightest of the naked-eye stars. Before the year 3000 B.C.
Egyptian temples were oriented to it. It is a double star, our
second nearest neighbor in the stellar universe. Its faint
companion, Proxima Centauri, is the nearest star to the sun,
having a distance of 4.16 light years. This indicates that it
takes light, traveling at 186,000 miles per second, 4.16 years
to bridge the distance between the star and the earth.

The most beautiful star cluster in the entire heavens is
located just about 18 northeast of Alpha Centauri. This
globular cluster, known as Omega (co) Centauri, is a gorgeous
object even with field glasses. It contains 5,000 stars, including
over 130 variables; and according to Professor Shapley it is
the nearest globular cluster, at a distance of 21,000 light years.
If the sun were removed to that distance, it would appear as a
star of the twelfth magnitude.

East of Crux and near Centaurus is Circinus, the Compass,
outlined by four stars. Alpha Circini is at the joint of the
Compass, Beta and Gamma at the two points. Triangulum
Australe, the Southern Triangle, is neighbor to the Compass.
It is formed by one second and two third-magnitude stars.

Stars of the Southern Skies

CRur

a .

f
/

% "Z.sry

?' f K

f / CIRCINUS

/-^. *">

/ ^ XI

PAVO /

\ 4

^ INDUS / i

V^*

: ^

..-i 1

/ .4

4c;

CENTAURUS -..

.* *-"

, f *>

"*^

^ t ..>

""S ""^

\ %
\

The faint constellation Norma, the Level, is just north
of the Triangle; Apus, the Bird of Paradise, is south. Ara, the
Altar, lies near the tail of the Scorpion and is composed mostly
of third-magnitude stars.

Now returning to the base of the exploring expedition, the
Southern Cross, the journey will continue west. The constella-
tion Carina, the Keel and Hull of the Ship, and Vela, the Sails,
are due west of Crux. Carina has a surprising number of ruddy
and variable stars.

A great number of travelers to the south are confused by
the False Cross, which is almost the exact replica of Crux
although it is slightly larger. This False Cross is composed of
Delta and Kappa Velorum and Epsilon and Iota (i) Carinae.

Eta Carinae is an irregular variable star in the midst of a
wonderful nebula. A glance at its remarkable history reveals
that, although it was fourth magnitude in 1677, it rivaled
Sirius in 1842. It later became invisible to the naked eye and
is today a telescopic object of nearly eighth magnitude.

About 90 west of the Southern Cross lies the second
brightest star in the whole heavens Canopus, Alpha Carinae.
Its magnitude is 0.9, and it is one of the very few super-giant
stars. This extraordinary star shines with a white light slightly
tinted with yellow, and although it is over 400 light years
away it appears bright to us because it radiates about 45,000
times as much light as the sun!

Eighteen degrees nearly southwest of Canopus is the Great
Magellanic Cloud (Nubecula Major) and about 70 due west
of the Great Cloud is the Lesser Magellanic Cloud. The Greater

Handbook of the Heavens

'"^N

\ ;
^ TOUCAN }}

ARA *

\ +

, r

\ PHOENIX \

\ J

\ HYDROS

1 1

t \ TEIESCOP1UM

ocm -^

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CORONA
AU5TRALIS

^ ^ <

ERIDANUS^/ ^-*
/ *\ HOROL061UM

Cloud is about 7 in diameter or fourteen times that of the
full moon, and is situated on the border of Dorado, the Sword-
fish, and Mensa, the Table Mountain. The Lesser Cloud, which
is less than 4 in diameter, lies in Tucana, the Toucan. Their
brightness, according to Sir John Herschel, "may be judged
from the effect of strong moonlight, which totally obliterates
the lesser, but not quite the greater." These great objects
are ma'de up of star clusters and nebulae. One of the members
of this cloud is the super-giant variable S Doradus which, at
its maximum, is half a million times brighter than the sun.
The actual diameter of this immense object is about sixty
million miles and it is intrinsically the brightest object
known.

About the same distance from the south pole as Crux
but on the opposite side of the heavens is the constellation
Eridanus, the River Po, with its bright star Achernar. Eridanus
flows in a long winding course from Rigel in Orion over
to Cetus, past Fornax and Phoenix to Hydrus, ending in
Achernar. The total length of this "Mississippi of the Sky"
is about 130. The constellation is composed mostly of fourth-
magnitude stars with Achernar standing out by virtue of its
brilliance.

Omicron (o) Eridani is a beautiful triple star in which
the two faint companions are over 43 billion miles from their
primary. In this region is located a planetary nebula described
by Lalande as the most extraordinary object of its kind he
had ever seen. It consists of an eleventh-magnitude star
surrounded by a circular nebula, and this set against a larger,

Stars of the Southern Skies 35

*>*

CHAMAELEON ^

j %.. ^ ^ TOUCAN

^' ^ APUS!\

/ \ I** \

^ ^ X - f -" GRUS

TRIANGULUM AUSTRALE ""*'

hazy cloud. Gamma Eridani is a fine contrasting double star,
magnitudes 2.5 and 10, separation 51 seconds. It is not in the
circumpolar section, however.

Eridanus is surrounded by nine constellations: Hydrus to
the south; Phoenix, Fornax, and Cetus to the west; Taurus on
the north; Orion, Lepus, Coelum, and Horologium on the east.

In the southeast corner of Toucan lies the Lesser Magellanic
Cloud, which is visible to the naked eye. Near by is the famous
globular cluster, No. 47 Tucanae, whose 22,000 stars blend
into a single star of the fourth magnitude when seen without
optical aid.

Directly south of this group is the constellation nearest
the south celestial pole, Octans, the Octant. Sigma (d) Octantis,
sixth-magnitude, may be called the Polaris of the south; it is
just a little less than i from the true south celestial pole.

Most of the names assigned to the constellations in this
region of the heavens are of modern origin because the greater
number of ancient astronomers lived in northern climes and
few ever went south to continue their work. Among the com-
paratively recently named constellations there appear Antlia,
the Air Pump; Chamaeleon; Circinus, the Compass; Columba,
the Dove; Crater, the Cup; Crux, the Cross; Fornax, the
Furnace; Horologium, the Timepiece; Indus, the Indian;
Mensa, the Table Mountain; Microscopium; Musca, the
Fly; Pictor, the Easel; Pavo, the Peacock; Telescopium;
and Volans, the Flying Fish.

Within 40 of the south pole there are stars representing
twenty-seven constellations, while in the same area around the

36 Handbook of the Heavens

northern pole only fifteen are represented. There are five
first-magnitude stars in this southern area and none in the
northern. The southern sky has about ten second-magnitude
stars, the northern about thirteen. So from studying both
northern and southern circumpolar skies it may be concluded
that the south circumpolar sky has the more brilliant constella-
tions and individual celestial objects.

But when the heavens 50 south of the equator are com-
pared with those 50 north, both sides come out just about
even in brilliance and interest. In all, 6,000 stars are visible
to the naked eye and they are shared almost equally by both
hemispheres.

Exploring among the Planets

CIRCLING forever about the sun, the planets move against the
background of constellations that form the zodiac. Day after
day they speed on their way, each a fascinating world revealed
to us only by reflected sunlight, for the planets are dark and
cold and borrow their brilliant, steady light from the sun.

Quickest of them all and closest to the sun is little Mercury,
which completes a revolution its year in about eighty-eight
days. With the same face always toward the sun because its
rotation period is equal to that of its revolution, one-half of
the planet is constantly scorched by the sun's rays while the
other side is locked in the perpetual cold and blackness of an
eternal night. However, owing to the constant rotation and
the slightly varying orbital speed (because of its elliptical
path), there is a fairly wide zone on Mercury along the twilight
line where the sun alternately rises and sets.

Even here the rugged surface is unprotected by an atmos-
phere and as a result drastic changes minimize the possibilities
of life on the planet.

Because of its nearness to the far more brilliant sun it is
on the average only 36 million miles distant this speeding
little globe is seldom seen. There are six two-week periods
during the year when it is well situated for observation.
These occur at the times of greatest elongation, or when the
planet is at its farthest distance from the sun as seen from
the earth. At the time of greatest eastern elongation, Mercury
sets soon after the sun and is seen in the west as the so-called
" evening star." About two months later, reaching greatest
western elongation, it will rise in the eastern sky soon before
the sun and be known as the "morning star."

Although visible only for an hour or so on each of the days
near elongation, Mercury shines with a brightness which varies
between that of Aldebaran and Sirius In a 2- or 3-inch tele-

Handbook of the Heavens

Ytrkes Observatory

VENUS. The planet Venus in cres-
cent phase, as she appears to the great
4O-inch refracting telescope at Yerkes.
She shines most brilliantly at such times
because of her nearness to the earth,
although but a fraction of her illumi-
nated surface is visible. It is when the
planet is but a slim crescent that she is
sometimes bright enough to cast a shadow.

PHASES OF MERCURY AND FEN US

1 Inferior conjunction

2 and 2' Greatest brilliance

3 Greatest elongation west

(a morning star)

4 and 4' Gibbous phase

5 Superior conjunction

6 Greatest elongation east

(an evening star)

scope, it appears as a pale yellow globe without surface detail,
but it displays phases similar to those of the moon, the causes
of which are shown in the diagram above.

Yellowish-white Venus at her best is more than fifteen times
as brilliant as Sirius, the brightest star in the heavens. She
takes about 225 days for her journey about the sun, traveling
along an orbit that is almost a perfect circle. Of all the planets,
she is the one most nearly comparable to the earth, for her
diameter of 7,575 miles is about equal to the earth's.

Venus has been observed to have a very dense atmosphere
which, however, contains practically no oxygen. It is possible,
however, that what has been observed is merely an outer
layer of atmosphere above a blanket of dense clouds which
surround the body. This suggests the possibility of oxygen
beneath the clouds sufficient to sustain life.

Like Mercury, Venus is never very distant from the sun.
For certain periods of time she is invisible to the naked eye,
although her periods of invisibility are not so frequent as those
of Mercury. She can be seen at the time of dawn or sunset, but

Exploring among the Planets 39

for no more than four hours at a time. However, Venus can
at times be seen in daylight with the naked eye.

Using a small telescope, we can watch Venus go through
phases just like those of Mercury. When the planet is farthest
from the earth, on the opposite side of the sun, she is "full";
when nearest the earth she is in crescent. The planet apparently
changes in size as it goes from crescent to full and back to
crescent, and its apparent diameter is six times as great in
crescent as when it is full. At its maximum brilliance, which
occurs 36 days before and after inferior conjunction, it is only
a crescent. It is then plainly visible and sometimes even bright
enough to cast a shadow.

Little of the surface has ever been seen except under very
fortunate and perhaps unique observing conditions. For this
reason the rotation period or day of the planet has not yet
been satisfactorily determined.

Both Mercury and Venus are visible for the greatest lengths
of time before sunrise and after sunset when they are at their
greatest western and eastern elongations, respectively. The
planets are brightest as they pass near the earth between the
elongations.

Traveling outward in the solar system, we pass the earth
and arrive at the ruddy Mars, which because of its color has
long been symbolic of the war god. It is only 4,230 miles in
diameter the smallest planet in the solar system except for
Mercury.

Mars goes through seasons similar to the earth's because
its axis is inclined to its orbit at an angle similar to that of
the earth's. Its day, ^ 27 m , is also comparable with the
earth's, but its year is nearly twice as long, for it takes 687 days
to complete its journey around the sun.

Aided by nearly perfect seeing conditions, several widely
known observers of Mars have distinguished linear markings
or " canals." At first they were attributed to the handiwork
of an advanced race of human beings who dug them to bring
water down from the poles, but this sensational idea has been
more or less abandoned. Indeed, the best observers are quite

Handbook of the Heavens

Retrograde Motion of M^irs
? Id net

Ytrkes Observatory

MARS. Prominent in this photo-
graph of Mars is the south polar cap,
which changes in size with the seasons.
Syrtis Major, the wedge-shaped area
extending toward the north, changes
color to correspond with the variations
in the polar cap and some astronomers
say it is a vast area of vegetation.

When the planets are in position 2,
Mars appears to be moving normally as
seen from the earth. But gradually the
earth passes Mars and the red planet
seems to move more slowly. In position
3 it apparently starts to move backward
and it continues so in 4 and 5. In 6 it
once again moves forward.

in disagreement as to whether the canals actually exist, for
it is a question of seeing detail at the extreme limit of visibility.

Easily picked up and observed when visible, Mars shows a
reddish surface with grayish or greenish markings. Even with
a small telescope some surface detail is visible. Because of
the great transparency of the Martian atmosphere, the
polar caps can generally be seen, except when they melt away
during the long summer. The pole caps are believed to be
either frozen water or carbon dioxide. Extensive reddish areas,
the continents of the early observers, and green or gray regions
or lakes are plainly visible with sufficient magnification.

For Martian observations with a small instrument a
magnification of 200 to 350 diameters is required before one
begins to see surface detail; with magnification of 300, one
begins to see polar caps, Syrtis Major, and other dark areas.

The red planet is attended by two moons, Phobos and
Deimos, neither more than 10 miles in diameter. They are so
close to the planet and so small that they cannot be picked up
with anything but the largest instruments. Phobos, the inner

Exploring among the Planets 41

Aft. Wilson Observatory

JUPITER. Ganymede, largest moon of Jupiter, throws its shadow on the belted surface
of the planet just before the satellite itself crosses in transit. The shadow is more easily
observed than the satellite which is soon lost on the planet's disk.

moon, speeds about the planet in less than one-third of a
Martian day and, interestingly enough, it rises in the west and
sets in the east.

Man has let his imagination run away with him in con-
templating the possibility of life on Mars. Whether the canals,
which some astronomers claim they have seen, are really
waterways and whether Syrtis Major is really a vast area
of. vegetation remain unanswered questions. And the ideas
of writers which picture the Martian man as anything from a
creature resembling an octopus to a highly intelligent being
are never ending.

Beyond Mars lie the diminutive asteroids, which are dis-
cussed separately elsewhere, and outside this belt of minor
planets is Jupiter, the largest planet in the sun's system. Pac-
ing slowly and majestically through the heavens, this great
cooled-off mass measures 82,880 miles from pole to pole.
It is outshone only by Venus and occasionally by Mars and
appears as a star much more brilliant than Sirius.

The amateur with his small telescope sees on Jupiter
soft shades of red, yellow, tan, and brown and a wealth of
other telescopic detail. Exceptional sight is not required to
get a clear view of the surface markings, and often a slight
haze or smoke in the air will steady the image. Barring the
belts which stretch in parallel lines across the disk, the chief
marking is or was the much-talked-of "red spot" of Jupiter.

42 Handbook of the Heavens

First discovered on the Jovian surface in 1857, it has disap-
peared and reappeared during the years. A curious feature of
this floating beauty mark is that it leaves behind it a hollow
space to mark its position each time it vanishes.

Of Jupiter's nine moons, four are visible even in a field
glass. Their positions in relation to the primary vary from
night to night, and indeed from hour to hour. Readily identi-
fied, they may be watched through many interesting hours
as they speed in front of Jupiter, throwing their shadows on
the planet, or vanish behind its giant disk or plunge suddenly
into its immense shadow. With care, it is possible to follow
the transits of their shadows, and to time their passages behind
the planet. A record kept of the moons from night to night
gives a graphic picture of their whirlwind paths about Jupiter.

The system of Jupiter and its moons presents a miniature
solar system, orderly and regular in manner. Each satellite
has a definite period (which you may time for yourself and
then check with an ephemeris); each has a definite path;
each travels in a set direction about the planet. Of the five
satellites that are not visible with small instruments, the
outermost two revolve about Jupiter in retrograde direction
from east to west. Discussion has arisen from this fact as to
whether they might not be captured asteroids and therefore
not originally members of Jupiter's system.

Saturn, the next planet beyond Jupiter, was the last
known to the ancients who were unequipped with telescopes.
And without telescopes, these ancients missed the most
wonderful sight to be found in the entire heavens. For Saturn,
with his beautiful rings, deserves that title; it presents a
magnificent spectacle.

The ring, for it appears as a single flattened object in a
small instrument, is poised high over the planet's equator,
its inside edge about 7,000 miles above the cloud surface. At
different times it appears to us inclined upward or downward
and it may even disappear for a time, because, when it is
viewed edge on, it actually is invisible. The rings are really
inclined at an angle of 27 and remain that way always; but

Exploring among the Planets 43

Barnard at Yerkes Observatory

SATURN. Saturn's rings, darkened in the rear by the planet's shadow, show up
beautifully in this photograph. Cloud belt surface and Cassini division of the rings are
defined.

as the planet moves around the sun, we see them at varying
angles from the front, the rear, or the side, according to
Saturn's position with respect to the earth.

Twice every thirty years Saturn reaches a place in its
orbit where the rings are tilted edge-on to the earth. At this
time they disappear when viewed with small telescopes and
are seen only in the most powerful ones as a fine needle thrust
through the globe. They are made visible at such times only
by the sunlight passing through them. The rings reflect so
much light that, when they present their broadsides to the
earth, the planet appears three times brighter than when the
rings are edgewise.

A telescope shows the divisions of the rings clearly. First
to be noticed is the Cassini division which divides the system
in two, and \^hich is easily seen in a small telescope. Then on
the outer ring we may see the faint, gray Encke division. This,
however, is illusive and is not always visible. The inner ring
gradually shades ^ff on the inner edge to meet the misty gray
border, the crepe ring.

The outline of the planet has been vaguely seen through the
crepe and outer rings, and stars have been seen through all
three, for they are composed of hundreds of tiny moonlets
revolving about the planet. The rings throw their shadow

44 Handbook of the Heavens

on the surface of Saturn as a dark, sharply outlined band.
In turn, Saturn throws its shadow across its belt of rings as a
black shape outlining one rim of the planet.

As for its surface, the ringed planet is somewhat like Jupiter
in that it too seems spanned by cloud belts. Little of these can
be seen, however, except under exceptionally fine conditions.
Occasionally a spot mars the complexion of Saturn, a spot
which is very useful in determining the precise rotation period
of the planet. The latest one, discovered in 1933, was called
the "white spot" and, although it has since diminished some-
what, it is still faintly visible.

Saturn, too, is blessed with nine moons and so outrivals
Jupiter, equaling him in satellites and bettering him in rings.
At one time, the planet was thought to possess ten moons,
but the tenth has, since its reported discovery, vanished and
there is some doubt about its existence. Without a more
powerful instrument than a 3-inch telescope it is difficult to
make observations of the satellites, although Titan frequently
can be seen with such a glass. Care must be taken to distinguish
them from the stars, but the moons Titan, lapetus, Rhea,
Tethys, and Dione are supposed to be visible in a 4-inch
telescope. They are named in the order of their observational
possibilities.

Discovered by Herschel in 1781, Uranus is the next planet
in order out from the sun. About 30,000 miles in diameter, it
can be seen as a sixth-magnitude "star" despite its 1,780
million miles' mean distance from the sun. It can be seen as a
naked-eye object by observers gifted with good eyesight.

Through a telescope it appears as a tiny green body with
vaguely defined belts stretching across its surface. No perma-
nent markings have been perceived upon it that can be used
for the exact determination of its rotation period, but this was
spectroscopically determined by Slipher who found the period
to be about 10% hours.

Uranus has four satellites, but they are all very faint and
cannot be observed except with large telescopes. The chief
observations possible for amateurs are the locating of the

Exploring among the Planets 45

planet and the mapping of its path among the stars. With the
aid of the charts published here, it may easily be followed.

Neptune was not discovered until 1846, but it wasxnpt long
afterwards that it was found to have one satellite. Although
Neptune is larger than Uranus, with a diameter of 3 1,000 miles,
Neptune's greater mean distance from the sun, 2,790 million
miles, makes it quite invisible except in a telescope of 2 inches
or greater aperture. It is, at its brightest, an object of eighth
magnitude, and with a little care it may easily be located.
Triton, its one satellite, is out of the reach of a small telescope,
but with such an instrument you should make out the greenish
color of the planet itself. Very much to be recommended is
the reading of the " Hints on Telescope Usage" (page 94),
which describes the proper technique for locating this planet
and other telescopic objects.

Completely out of the range of small instruments, and
indeed not easy for a 1 5-inch refractor, is Pluto, found after
years of search in January, 1930. It is so far distant from the
sun that it takes 248 of our years to complete one revolution
and consequently spends 20 years within the boundaries of
one zodiacal constellation. It is still near its discovery point
at Delta Geminorum. We know little more about it than that
it is about one-half the size of the earth and has no satellites
yet discovered.

An excellent piece of naked-eye observation of any one of
the planets is the mapping of its path among the stars. Sooner
or later (except in the cases of Venus and Mercury which are
invisible at such a time) the observer will notice the retrograde
motion of the planet. That is when it seemingly turns around
and backtracks along its former path. But before it has gone
far it will turn again and proceed in its original direction.
This is an interesting phenomenon and is an effect caused by
the relative movements of the earth and the planet under
observation. The diagram on page 40 shows this for the earth
and Mars. In the following planet maps retrograde motion
appears in the path of almost every planet during the period
covered by the maps.

Planet Maps

In the following planet maps, the apparent path of each of
the planets is indicated by a long curved line. The dates locate
the position of the planet at different times during the year.

To learn whether Venus, for instance, is a morning or
evening star, refer to these maps to learn in which constellation
it is located at the time. If the path is dashed in the maps of
Mercury, Venus, and Mars, the planet is invisible. If it is
visible, refer to the constellation maps to learn when and in
what part of the sky the group containing the planet may be
seen.

The charts for Jupiter and Saturn show stars to the limit
of naked-eye visibility. The charts for Uranus and Neptune
show stars down to 93. Only the naked-eye stars are labeled
on these two charts. Uranus is on the limit of naked-eye
visibility and hence its magnitude is close to that of the three
BD stars (see the Bonn Durchmusterung^ Argelander's great
atlas and catalog of stars to declination 2). Neptune is
much fainter, somewhat brighter than the fainter stars shown.

4 6

Planet Maps

Handbook of the Heavens

Planet Maps

Handbook of the Heavens

A Q U A R I U S

Exploring on the Moon

SLOWLY the sun rises over the barren, sandy wastes and the
great jagged mountain peaks that form a conspicuous part of
the moon's surface. Slowly it reveals to the patiently waiting
astronomer the landmarks that make the moon the most
interesting planetary object for amateur observation. The
amateur astronomer finds that the moon's topography, studied
even with a small telescope, field glass, or the unaided eye,
is far more fascinating than the earth's.

But, just as terrestrial geography is systematic, so is
lunar topography, and to make a good beginning it is wise to
learn the maria, or seas, so named by the early lunar observers.
These great areas are really dark-colored and comparatively
smooth plains. The first large one visible as the moon swings
around the earth after its "new" phase, and one that is easily
recognizable by its isolation, is Mare Crisium. As the moon
waxes, the next to appear are, in order: Mare Foecunditatis,
Mare Nectaris, Mare Tranquilitatis, and Mare Serenitatis.
When all these are in view, the moon has reached its first
quarter.

It will then seem to grow to a full moon, become again a
quarter, then a crescent, and finally disappear from view.
To the observer of lunar surface markings the phases are
significant because the best place to observe a lunar feature
is at the time of sunrise or sunset on that object. It is then
brought into sharp relief by the shadow it casts and is located
on the terminator where sunlight ends and shadow begins.
The terminator is constantly shifting across the moon with the
changing phases.

The diagram on page 53 illustrates these phases and their
cause. The inner circle shows how the moon really is as it
revolves around the earth; the outer circle, how the lighted
half of the moon appears to us. The phase varies with the

52 Handbook of the Heavens

angle from which we observe the parts of the moon lighted
by the sun. At times a portion of the moon (not lighted by
the sun) appears faintly illuminated. This is "earthshine"
the light which the earth has reflected to the moon which
makes visible, areas of the moon which would otherwise be
dark and invisible. Sometimes in a clear atmosphere one
can distinguish with the naked eye the seas lighted by earth-
shine and with a telescope certain other of the major details.

Nightly observations of the moon reveal that, on the
average, it rises about 50 minutes later each evening. This is
because the moon, in its monthly revolution around the earth,
moves approximately 13 eastward through the zodiac in a
day. As a result, should the moon rise at 10 P.M. on one evening
it would still be below the horizon at the same time next night,
and 50 minutes would have to elapse for the earth to rotate
enough to allow the satellite to appear over the eastern horizon.

Between first quarter and full moon Mare Vaporum, Mare
Frigoris, Mare Imbrium, Mare Nubium, Mare Humorum, and
lastly the great Oceanus Procellarum, the Ocean of Storms,
appear. This last is the most easily visible to the naked eye.

On the northwestern edge of Mare Tranquilitatis, near
the Mare Crisium, will be found the Palus Somnii, the Marsh
of a Dream. On the northern " shore" of Mare Imbrium will
be found two promontories, Promontory Laplace and Prom-
ontory Heraclides, enclosing the semicircular Sinus Iridum,
the Bay of Rainbows. Some of the mountains bordering on
this bay are said to have peaks towering to 20,000 feet.

Connecting with the side of the Mare Imbrium is the Sinus
Aestuum, the Bay of Hearts, and still farther soxith and
almost in the center of the visible hemisphere of the moon
is the appropriately named Sinus Medii. To the west of Mare
Imbrium can be found the Palus Nebularum, the Marsh of
Clouds, and the Palus Putredinus (between Imbrium and
Serenitatis) . The inconspicuous Sinus Roris is north of Procel-
larum and connects with Mare Frigoris.

Once these maria, marshes, swamps, etc., have been
discerned, it is natural for the telescopist to develop a strong

Exploring on the Moon

Gibbous

Full moon

Gibbous

o c

Earth

Crescent
Last quarter %/^

Yerkes Observatory

MOON. Near the sunrise line are the 7Y/ MOON'S PHASES. The inner

lunar Apennines, brought into sharp circle represents the moon as it appears

relief by the sun's slanting rays. Some from a point above the earth's pole; and

of the towering peaks on the dark side the outer circle shows it as it is seen in the

are tall enough to be seen while the sky (considered apart from the diagram),
valley below is in darkness.

interest regarding the circular, crater-like objects, which, next
to the seas, are the most conspicuous objects to be observed on
the moon.

The largest of these crater-like formations are the "moun-
tain-walled plains/' They range in size from 60 to 150 miles
in diameter. These plains, which closely resemble smaller
maria, are encircled by mountain masses of different heights.
The interior is much depressed below the level outside the rim,
this rim or rampart often rising but little above the sur-
rounding land. Typical of these mountain-walled plains are
Clavius (the largest), Schickard, Ptolemaeus, Maginus, and
Grimaldi. All of these and numerous other objects appear on
the moon map on page 59.

The second group of crater-like features is the " mountain-
ringed plains." The ramparts are practically circular, 10 to
60 miles in diameter, with steep inner slopes and gentle
outer slopes; the floors are deep depressions; many craters
may be discovered on the tops of the walls or on the outer
slopes; often there are central peaks: Theophilus, Aristillus,
Aristoteles are typical of these. Copernicus and Tycho also
belong here and are noted for the striking ray systems radiat-

54 Handbook of the Heavens

ing from each, these being seen best at the time of full moon.
The rays from Tycho extend for hundreds of miles over moun-
tain and plain without interruption. Plato is unique in color
and easily located. It was in this crater that Pickering dis-
covered monthly variation, which he supposes is caused
by vegetation. Herschel is a small ringed plain north of
Ptolemaeus. When on the terminator it can easily be dis-
cerned with eighteen-power binoculars and is a beautiful
sight, small and round with a very bright inner wall. It
thus makes a fine test for low magnification.

The third type consists of the " craters" or " crater rings."
These craters proper are but 3 to 10 miles across and are too
small to be picked up with low telescopic power. They are
almost perfectly circular, very numerous, and of much interest
to observers with telescopes using 50 to 500 diameters. They
are too small to be indicated on the lunar chart, which shows
only the larger and more easily observable objects.

Of the mountain ranges, the more striking ones are named
after terrestrial ranges; for instance, the Alps, Apennines, and
Carpathians, all of which are part of the irregular border of
Mare Imbrium. In these lunar ranges are many hundreds
of peaks whose elevations average over 10,000 feet. Some rise
higher; Mt. Huygens in the Apennines and Mt. Hadley in
the Palus Putredinus rise to heights of 15,000 to 18,000 feet.
The Leibnitz range is the highest on the visible lunar surface
and some of its peaks are perhaps higher than Mt. Everest, a
few being said to attain 30,000 feet. The range is located on
the extreme southern limb and so it is seen only in profile.
All these ranges resemble earthly mountains, although erosion
is commonly supposed to be quite absent; this may not be
true, however, as the Riphaen mountains (for example)
appear to have suffered much erosion.

The crater Aristarchus is notable as being the brightest
object on the moon and by early observers it was often
mistaken for an active volcano. The deepest depression to
be seen is the small crater Newton. The Straight Wall is a
strange object and not very difficult to pick up. When the

Exploring on the Moon

Yerkes Observatory

OCCULTATION OF ALDEBARAN. At the left, the star is seen just before it dis-
appears behind the dark limb of the moon. The second picture was made just as it was mov-
ing from behind the moon, on the lighted limb, and the third plate was exposed less than
two minutes after the star had completely emerged from behind the satellite. The panel is
arranged to present the phenomenon as it appears to the naked eye,

light is right there is a bright edge with a narrow black border.
It is believed to be a "fault" and is located in the south-
western corner of Mare Nubium. Look also for the Straight
Range between Plato and the Promontory Laplace. This
formation assumes a nearly uniform, straight line, east and
west, about 45 miles long, with at least a dozen peaks dis-
cernible with high enough magnification. The central peaks in
many of the craters and crater-like objects have been success-
fully used to account for the lunar formations in both the
volcanic and meteoric theories of the moon's origin.

There is no end of interesting material for moon explora-
tions, because more advanced work in observing, besides
touching the foregoing types, also brings in isolated mountains,
dome-shaped hills, crater chains, crater pits, rills, many twin
craters, multiple craters, ruined ring plains, hilltop craters, and
other special formations.

In addition to presenting many features of interest in its
topography, the moon plays an important part in several
spectacular celestial phenomena. Chief among these are
occultations and eclipses.

As the moon moves through the sky, it frequently glides
in front of a star or planet, blotting it from view. Since the

56 Handbook of the Heavens

moon always moves eastward in the sky, the object always
disappears behind the eastern edge and reappears on the
western limb. In an occultation, as it is called, of a star below
fourth magnitude a telescope is usually necessary because the
moon's light cuts the star from naked-eye view before its
disk actually eclipses it. And it must be remembered that an
astronomical telescope reverses the object. Therefore a star
which, to the naked eye, appears to the left of the moon will
seem to be at the right in the telescope.

The most interesting effect is when the dark side of the
moon is in the lead (any time before full) and the star dis-
appears without warning. Another unusual sight is the occulta-
tion of a double star.

The disappearance of the star in an occultation is instan-
taneous because of the fact that there is no atmosphere on
the moon and because even the brightest stars appear and
disappear as mere points of light. The abruptness of these
disappearances and reappearances is indeed startling.

The exact place of the moon in the sky can be determined
and a knowledge of its motion refined by observations of
occultations. It is essential that they be accurately timed if
the observation is to be used for this purpose. Of course, it
is much more difficult to predict them than to observe or time
them. This takes almost an expert but amateurs can do it.

The sight of the moon cutting off the light of a distant
star is, however, less spectacular than that of the moon itself
dropping from sight in the shadow of the earth. For, as the
satellite swings about in its orbit, reflecting the sun's light,
it must pass behind the earth and will occasionally be eclipsed.

Usually it passes above or below the earth's shadow, but
sometimes it does not. And then, with the sun's light shut off,
it turns a dull red and becomes nearly invisible. This occur-
rence, an eclipse of the moon, is illustrated by the diagram on
the following page.

In actual observation of a lunar eclipse, even in the midst
of totality, it is noted that the moon does not really disappear
but only dims and changes color. For even when the moon is

Exploring on the Moon 57

N x t ,Moon eclipsing sun

/ s -T--^

"Moon eclipsed by earth's shadow

in the midst of the earth's shadow, it does not lose all of the
sun's light because some of it is refracted (bent) by the earth's
atmosphere. Red, orange, and yellow light pass through the
atmosphere most easily and for this reason the moon appears
a copper color during the eclipse.

It can be readily seen by the diagrams that eclipses of
the moon, when they take place, are visible over half the earth
at one time, while eclipses of the sun are visible only in small
areas. For this reason, even though eclipses of the sun are
more numerous, an observer at a given spot on the earth
would see lunar eclipses more frequently than those of the
sun. Furthermore he would see the moon eclipsed for a longer
time. The moon, therefore, plays a part in two of the most
interesting phenomena of the skies.

MARE IMBRIUM REGION

photographs yet made, this beauti
" " " It is keyed for study.

Mi. Wilson Observatory

OF THE MOON. A portion of one of the finest moon
ful picture shows Mare Imbrium one of the so-called

I Plato

14 Carlini

27 Timocharis

2 Pico

15 C. Herschel

28 Archimedes

3 Condamine

1 6 La hi re

29 Autolychus

4 Maupertius

17 Lambert

30 Aristillus

5 Bianchini

18 Euler

31 Thaetetus

6 Bouguer

19 Pytheas

32 Cassini

7 Foucault

20 Gay Lussac

33 Piton

8 Harpalus

21 Eratosthenes

34 P. Smyth

9 Sharp

22 Wolf

35 Mt. Blanc

10 Louville

23 Mt. Huygens

36 Kirch

ii Mairan

24 Mt. Bradley

A Teneriffe Mts.

12 Leverrier

25 Conon

B Straight Range

13 Helicon

26 Mt. Hadley

C Prom. Laplace

D Sinus Iridum *

E Prom. Heraclides

F Carpathian Mts.
G Apennines
H Palus Putredinus

I Caucasus Mts.

J Palus Nebularum
K Alps

L Alpine Valley
M Sinus Roris
N System of clefts southwest

of Archimedes
O Rays extending from
Copernicus

Meteors and Meteor Showers 61

YerkfS Observatory

METEOR TRAIL. An errant me- METEOR RADIANT. The paths

teor glides into the star field of a Barnard of meteors belonging to a swarm trace

photograph. backward to a common center.

Composed of stone or metal or a combination of the two,
the average meteor probably revolves in an orbit within the
solar system and is subject to the gravitational attractions of
any large bodies which it may approach.

Many are found in groups which follow nearly regular:
orbits around the sun. A few of these orbits may be identified
as belonging to comets which may no longer exist. It is thought
that these meteors are simply the remnants of the comet which
has broken up or which is in the process of breaking up.

The debris from the disintegrating comet becomes scattered
around its orbit, and when the earth happens to cross one of
these orbits, as it frequently does, many more meteors plunge
into the atmosphere than do usually. If a large number of
meteors are gathered into a central swarm traveling around
the sun in the comet's orbit, and the earth intersects this
swarm, the meteors can then be counted by the thousands.

This explains the periodic meteor showers and it explains
the strange periodicity of the Leonid shower, to take a definite
example. Every thirty-three years a big shower is seen, and
the display in 1833, previously mentioned, belongs to this
group. This unusual shower which greets the earth three times
a century occurs when this planet cuts into the main swarm.
During intermediate years the earth swings through the
meteor orbit without meeting the main condensation, but,

62 Handbook of the Heavens

nevertheless, hundreds of stray meteors are caught. In some
cases, like that of the Perseids, the bodies have become well
distributed about the orbit so that one year is about as good as
another.

Recently the Leonids have been very disappointing to
amateur and professional astronomers who were expecting
great displays. Meteor authorities attribute this disappoint-
ment to the fact that Jupiter may have drawn the Leonid
swarm away from its former orbit so that the earth does not
cut through the densest part at the same time it did formerly.

Of course, the best nights on which to watch for meteors
are nights on which showers are due, for at these times it
may happen that as many as 500 meteors are seen by one
observer between midnight and dawn. During a shower the
meteors seem to radiate from some particular constellation,
and this point is called the radiant. Usually the shower takes
its name from the name of the constellation in which its
radiant is located.

This radiant point is only an illusion, and the meteors
have absolutely no connection with the constellation from
which they appear to emanate. This is brought home by the
fact that the star group which marks the radiant may be fifty
light years away, while the meteors themselves, when seen,
are only some fifty miles distant. The illusion of the radiant
is caused by the fact that when parallel lines are extended
they appear to converge. It is the familiar effect of railroad
tracks converging in the distance. Since meteors travel in
more or less parallel paths through the atmosphere, the effect
is similar.

Amateurs will find much pleasure and enjoyment in observ-
ing and recording meteors any night during the year and can
be of material assistance to the science of astronomy. Even
the record of a single meteor may prove valuable when com-
bined with the reports received from other observers in the
region. And the apparently unimportant results of a night's
observation may become extremely significant to an expert
who can compare them with other reports.

Meteors and Meteor Showers 63

If only one person is observing, it is best to use a star chart
and plot the path of shooting stars on it, together with a note
of the time, as in the diagram on page 61. When this is done
it may be noticed that some of the paths, traced backwards,
will indicate a common point of origin. If two people are
observing, it is suggested that one person observe and the other
record the observations. In this way a constant watch is kept
on the sky and no meteors are likely to escape attention.

When more than one person observes the same sky area
during the same time, care should be taken not to combine
totals, as the unit used in recording and computing meteor
falls is the number seen by one observer per hour. If possible,
each meteor should be timed separately; otherwise the number
seen every five minutes will do.

When measuring paths, trails, or positions of particularly
bright meteors, astronomers use the unit of i. The distance
from the true horizon to the zenith is 90; it is 5 between the
pointers of the Big Dipper; the belt of Orion has a length of 3.
These dimensions can be used to judge other distances.

In estimating the magnitude of a meteor it is best to com-
pare its brightness with that of familiar stars. Capella and
Rigel are of the first magnitude; Polaris is a second-magnitude
star; the stars in the constellation Delphinus are of the third
and fourth magnitude.

The following chart is a suggestion made to expedite the
recording of the meteors whether a shower is being observed
or whether it is just an average night's fall.

The observer should be warned that only on the nights
indicated by asterisks are there actual showers, when large
numbers of meteors may be expected. The unstarred nights
have been reported as favorable by a large number of observers,
and the meteors seem to show some relation to the radiant
indicated. However, in the present state of knowledge, it is
impossible to prepare a complete list of radiants and showers.

Much research is being done on this problem and a large
number of careful observations are necessary to solve it. The
American Meteor Society, Upper Darby, Pennsylvania, will
give specific directions to those wishing to make observations.

6 4

Name

Handbook of the Heavens

Date

Sky

Seen

Time

Speed

Color

Magni-
tude

Remarks

First

Last

12:50

Regulus

Horizon

Fast

White

Trail 7, lasted 2 sec.

12:53

7 Leonis

Spica

Slow

Yellow

No trail

12:59

6 Leonis

Polaris

Fast

White

Trail, lasted 3 sec.

CALENDAR OF GOOD NIGHTS FOR OBSERVATION f

Date

Shower

Remarks

June September

7 Draconids
a Capricornids
a-0 Perseids
5 Aquarids
Perseids
a Aurigids
K Cygnids
o Draconids
Draconids
e Perseids
Quadrantids
e Arietids

(head of Draco)
Orionids
e Taurids
e Taurids
Leonids

Andromedids

Geminids
Quadrantids
K Cygnids
a Aurigids
f Bootids
Lyrids
7 Aquarids
f Herculids
tl Pegasids
a Scorpiids
t Draconids

Slow; with trains
Very slow; bright
Swift; streaks
Long paths; slow
Famous shower; swift
Very swift
Medium
Very slow
Bright
Swift
Slow
This shower is scheduled to return
in 1940
Very slow; fireballs
Swift
Slow; fireballs
Very slow, bright
Famous shower every 33 years
but disappearing
Famous shower disappeared in re-
cent years. Slow, Biela's Comet
Fine shower; white
Good; medium speed
Slow; trains
Very slow; fireballs
Swift; streaks
Swift; streaks
Very swift; long paths before sunrise
Swift; white
Very swift; streaks
Very slow; fireballs
Very slow

Tulv 1 8^0

Tulv 2C Aug. d.

*Tulv 2C 10

*Aug. 1012

Aug. 12-Oct. 2

Aug. 10-20

Aug 2123

Aug. 21-31

Scot. 7i ;

Oct. 2

*0ct. Q

Oct. 12-23

*0ct. 18-20

Oct. 3O-Nov. 17

Nov. 3 i c

*Nov. 13-15

Nov. 1727

*Dec. 10-12

*Tan. 2-1

Jan. 17

Feb. 5-10

Mar. 10 12

*Apr. 20-22

*May 6

May 1 1-24

May 30

June 2-17

June 27-30

* The best showers. t Adapted from Norton with modifications approved by Dr, C, P. Olivier.

Comets

ALTHOUGH thousands of comets revolve in regular orbits
around the sun, it is seldom that one becomes visible to the
naked eye. However, nearly always there is one within reach
of observers using a small telescope.

When, from time to time, one of these space wanderers
does mushroom into sight, it may grow brighter than Venus
and even become visible in the daytime despite the over-
whelming brilliance of the sun.

Although tremendous in size, comets are really collections
of small particles of matter so widely scattered that stars
may be seen through thousands of miles of comet material.
The nucleus, when present, is the densest part of the comet
and is a meteoric mass at the central part of the head. Envelop-
ing the head and visible in all comets is the coma, a faintly
luminous gas cloud which often sends out a series of concentric
shells or "envelopes."

The coma is a large mass, nearly synonymous with the
head, and the matter it sends out either as envelopes or as
plain material seems to move steadily toward the sun. When
it reaches a certain limit it seems to be repulsed by the sun,
and it is then thrown back to form the tail. This is the most
spectacular feature of naked-eye comets, although some do
not have tails. When present, the tails always stream out into
space away from the sun. Tail, head, and coma are generally
composed of hydrogen, hydrocarbons, sodium, and other
metallic vapors, together with fine solid materials.

The average diameter of comet heads varies from 10,000 to
100,000 miles, while the range in the length of tails in naked-
eye comets is from 5 million to 200 million miles. The tail is
shaped somewhat like a horn, and consequently it may be
millions of miles wide at its end.

Comets differ more in brightness than do any other celestial
bodies. Some have been second in brightness only to the sun

66 Handbook of the Heavens

and moon, while others are barely seen with powerful tele-
scopes, and there are some that are so dim as to be beyond
visibility.

Comets are often discovered by astronomers who con-
tinually sweep the skies with their telescopes searching for
them. Among these comet seekers are numerous amateurs
who add considerably to the total. Many new comets also
have been found in recent years by photography. A comet is
usually identified only after hours spent in visual or photo-
graphic observation of its motion.

When an observer comes upon a diffuse object in the field
of the telescope, he should first refer to a reliable atlas to
eliminate the possibility of its being a nebula or cluster. If
it is comparable in brightness with average Messier objects
in the surrounding field, the chances are that it is a comet.
He should then plot its position with extreme accuracy and
telegraph the Harvard Observatory, briefly stating its exact
location and appearance. This will assure him of priority of
discovery in the event that it is a comet. However, if it is
possible to get in touch with an observatory or with an expert
who has a list of current comets, it might be best to do this
first before telling Harvard.

Perhaps for his first adventure in comet hunting the
observer would prefer to feel more sure of himself before
notifying the observatory. If this is the case, he may discover
some displacement of the object from the original position
by observing it on subsequent evenings. The evidence of any
motion in relation to the neighboring stars leaves little doubt
that it is a cometary object of which the observatory 'should
be notified.

Of course, this may be a known comet for which he cannot
claim the credit of discovery, but he will at least have experi-
enced the thrill of discovering it for himself.

Unusually brilliant comets are frequently given the name
of their discoverers, as, for instance, Donati's Comet. A comet
is also technically designated by the year in which it is dis-
covered, followed by an a if it is the first to be found in a

Comets

Mt. Wilson Observatory

II ALLEY 1 S COMET. Halley's
Comet photographed during its visit
to the earth in 1910. One of the most
spectacular of the naked-eye comets,
and the last great comet to be seen to
date, it will not be visible again until
1986.

COMET DEBRIS. As a comet dis-
integrates, it leaves behind it widely
scattered meteoric material which con-
tinues to follow the comet orbit.
When the earth meets such a swarm, we
have a " meteor shower."

given year, a b if it is the second discovered, etc. Another
method of classification is the year followed by a Roman
numeral giving the order of perihelion (point nearest to the
sun) passage, as Comet 1816 II. Both designations are used,
the latter being applied after all the year's comets' perihelion
passages have become known, while at first only the order
of discovery can be used.

Comets travel in three types of orbits: elliptical, parabolic,
and hyperbolic. Those which follow hyperbolic and parabolic
orbits will never again swing around the sun, once they have
made this curve. Instead they continue on and on, far out
beyond the solar system.

But those whose orbits take the shape of ellipses do revolve
about the sun in periods that vary according to the individual
comet. About fifty are known to have periods of less than

68 Handbook of the Heavens

100 years, while some are thought to take 10,000 years to
complete one revolution. The Comet 1864 II had a period of
2,800,000 years and its aphelion distance was 40,000 astro-
nomical units, or 3,720 trillion miles.

Short-period comets are those which have periods of just
a few years, and of these thirty-six complete a revolution in
from five to seven and one-half years. They form a definite
group, all moving in similar orbits, all being quite faint,
and most of them having no tails. The aphelion (farthest
distance from the sun) of each of these comets is very near
to the orbit of Jupiter, and so it has been suggested that these
comets, formerly traveling in parabolic orbits, were drawn
into their present paths by Jupiter's gravitational attraction.

Most comets move just as they would be expected to in
free space under the laws of gravitation, but there is one
striking exception. This is Encke's Comet, which has the
shortest * period known 3.3 years. The period of Encke's
Comet is observed to be shortening steadily, and this phe-
nomenon is difficult to explain. It is believed that the comet
meets with some unknown resistance in its path. This resist-
ance causes a greater relative gravitational effect from the
sun, and so the comet falls toward the latter more, shortening
the orbital path and therefore its period of revolution.

The long-period comets show little evidence of having been
captured by any of the planets. They are often of great bril-
liance, while those of shorter period are usually very faint.

Double Stars

Two tiny points of brilliant light, one a rich gold and the
other a deep blue, glowing in a field of coal-black sky the
double star Albireo, seen through a 3-inch telescope!

It can be seen with a field glass or a small telescope, and
it leaves an impression on the memory as clear as that left
on a photographic plate. Albireo is the star Beta Cygni, the
fourth brightest star in the constellation of the Northern
Cross, which begins to rise in early May evenings.

Albireo is only one of thousands of stars of its type which
stud the heavens, their concealed beauties unsuspected until
they are viewed with the telescope. These thousands of
" double stars/' as they are called, are for the most part
binary systems. That is, they are two stars which, although
not actually in contact, have a physical connection with each
other, for they rotate about a common center of gravity.
Albireo is thought to be such a system.

But there is another variety of double star in which the
components are not connected but are simply so situated along
the line of sight that they appear to be together, although
one may be hundreds of light years behind the other. These
stars must usually be within a half minute of arc of each other
to be considered as "optical doubles."

Then, too, there are the " naked-eye doubles" which seem
to the unaided eye to be very close together but which generally
have no physical connection. Of these Mizar (Zeta Ursae
Majoris) and its near neighbor Alcor in the Big Dipper are
the most famous. As they are brought under the telescope,
one of the pair suddenly becomes a double in its own right,
so that three stars appear in the field. Other naked-eye doubles
include Alpha Capricorni and Epsilon Lyrae.

As previously mentioned, the majority of the twenty
thousand or so close visual doubles actually revolve about

70 Handbook of the Heavens

a common center of gravity and are called physical doubles.
Some of these binary systems have periods of revolution of
five to ten years, although many of them have far longer
periods. The motion as we see them from the earth are in some
cases so slow that it takes centuries to establish an orbit.
Until comparatively recent times, all double stars were
thought to be composed of two stars that were nearly in the
observer's line of sight.

It was Sir William Herschel who accidentally stumbled upon
the fact that in most cases the two stars actually do revolve
around each other. He had, in 1789, turned his telescope to
the task of observing a double with the intention of measuring
the distance between the brighter star and the supposedly
far more distant dimmer one. Instead, he made a new dis-
covery that in most cases components of a double star
actually revolve about each other, or rather about a common
center of' gravity. Herschel's catalogues contain about 700
double stars, including many important binary systems.

The photographs on page 73, taken over a period of twelve
years, clearly demonstrate this discovery of Herschel's. In
them is shown the rotation of the two components of the binary
Kriiger 60.

The discovery of new double stars is made by simple
telescopic observation, a departure from the usual lines of
research. Professional hunters of doubles find that they need
suitable atmospheric conditions, a trained eye, a telescope
of good optical quality and large aperture, and a micrometer.
The Lick 36-inch refractor, used in a recent search through a
limited portion of the sky, revealed more than 4,300 new
pairs. Work now in progress in the southern skies is expected
to disclose thousands more.

Yellow and purple, a magnificent combination of colors
seen at its best in the natural setting of the stars, form the
scheme of the star Eta Cassiopeiae, a double that can be
found without difficulty. Also among the circumpolar star
groups are the previously mentioned Mizar and Alcor, which
appear as double to the naked eye and triple in a telescope.

Double Stars

Telescopic

View

Qt+ ^x-~~"~

""s^

, \

*. -* <' *

t \

CYGNUS "* / ' * ;

f \ . '

^-*- \ .

/ x ' x x

j i/a Albireo s ^

\ /' " ""

Binary System

But this three-star view approaches no limit, for deep in
the Nebula of Orion is imbedded a jewel among star sights,
Theta, a quadruple whose components form the Trapezium.
Its stars, ranging in magnitude from 4.7 to 8, are white, lilac,
garnet, and reddish. Although this quartet can be observed
with a 3-inch glass, a larger glass reveals it in even more
splendor, and more stars can be seen (see Orion, page 81).

It might be well to mention that there is, so far as we know,
no relation between double stars and star clusters. The cluster
is by no means a further development of the double and
multiple stars which we have been considering, for a cluster
is a grouping of a considerable number of individual stars
which may be in themselves single or double.

In many cases, the component stars of a binary system are
so close to each other that the most powerful telescopes in
the world today cannot separate them. It is only when they
are subjected to the searching eye of the spectroscope, astron-
omy's second greatest weapon, that they are revealed.

When a star is racing toward the earth, the lines of its
spectrum as seen in the spectroscope are displaced toward
the violet end of the spectrum; and when it is speeding away,
the lines are displaced toward the red. If the spectrum of a
star shows that some of the lines are displaced toward the
red, while others are moved toward the violet, then we know
that there are in reality two stars moving in opposite directions.
This telltale split spectrum is a sure sign of a close double,
and, as they are known to be twin stars only because of the
spectroscope, this type is known as the " spectroscopic binary."

72 Handbook of the Heavens

Should the orbital plane of the pair be at right angles to
the line of sight, so that neither of the stars appears to be
moving toward or away from the earth, the spectroscope is
unable to detect their motion, and doubtless many doubles
under such a condition are still awaiting discovery. If the
orbital plane of the pair passes through the earth, the two stars
will eclipse one another, and they are known as eclipsing
binaries. Such stars are often variable; see the chapter on
"Variable Stars" (page 88).

The great range of colors may best be shown by scanning
the following list. Yellow and blue, orange and emerald, topaz
and green are only a few of the descriptive comments you see;

A SELECTED LIST OF BEAUTIFUL DOUBLES

Double star

Magni-
tude

Separa-
tion,
seconds

Remarks

f Ursae Majoris
v Draconis

2- 4

c c

Mizar
A beautiful object

6 Cephei .

1 6 7 C

4.1

Yellow and blue (variable)

y Andromedae

2 A.- C

Orange* greenish blue

ct Capricorn! ...

-J A

176

Telescopic double-double

T Leonis

$ 4.- 7

Contrasting colors

y Leporis

18-64.

Yellow and garnet

6 Orionis

2 c 6 o

\Vhite and violet

e Pegasi

2 q- 8 c

118

Yellow and violet

17 Persei

1 Q- 8 ;

White and blue

8 Cyeni

1.2- C 4.

Gold and blue

f Lyrae ...

4. 7 c Q

4.4.

Topaz and green

c Lyrae

r r

2O7

Double-double with high power

y Virginis

1717

Both yellow* easy

y Arietis

4. . 2 4. 4.

Good test for small glass

77 Cassiopeiae ... ...

17-76

Yellow and purple

tx Geminorum

2 1

Both white

y Delphini .

A C C C

Yellow and bluish green

e Bootis

1-61

Orange and green* superb

a Canurn Venaticorum

1 2 C 7

Beautiful pair

Serpentis ...

A A 2

Both yellow* very fine

55 Piscium

q- 8 2

Yellow red or purple

Tauri

c- 8

Red and blue

f Coronae

4. I c

\Vhite* greenish

5 Corvi

1- 8 c

24.

Yellow and purple

Aquarii

4.- 4. I

Easy though close

CL Tauri

I-II 2

Fine in 4-inch telescope

Double Stars

1908

1915

1920

Ytrkes Observatory

DOUBLE STAR KRUGER 60. Far out in the depth of space two stars swing about
each other and photographer Barnard, at Yerkes Observatory, captures them on his
plates. The pictures prove beyond all doubt the rotation of this binary star.

and when one of these pairs bursts upon your field of vision,
it finds you totally unprepared for the sight.

Experienced observers find that the clearest nights, when
the stars are twinkling excessively, are not the best times for
seeing doubles; a calm night with a tranquil atmosphere, not
disturbed by wind and layers of air of unequal density and
often with something of a mist or haze, helps to keep the
stellar image motionless.

A highly corrected telescope objective or a reflecting
telescope mirror will show the colors to best advantage in
resolving stars. It is advisable to use the lowest magnification
that will resolve the stars at the time. Those of very wide
separation can be split with field glasses. Some, like Epsilon
Lyrae, are double with low power and quadruple with high.

Certain doubles are remarkably beautiful and can be
profitably used as special ones for demonstration to new
groups of enthusiasts. Such are Albireo, Castor, Gamma
Andromedae, Epsilon Bootis, and Epsilon Lyrae. They vary
in magnification needed, Albireo using 18 diameters, Epsilon
Bootis 150.

The foregoing list is but a suggestion; the heavens con-
taining a vast wealth of material to use any clear night of
the year starry gems that can be revealed only by a good
telescope and careful observing.

Solar Observations

WHAT would happen if the sun suddenly ceased to shine,
or if it changed its position in relation to the earth, or if it
suddenly blazed up to many times its present light and
heat?

The results are too horrible to contemplate, but certainly
an object that plays so important a part in our lives as does
the sun is worthy of a good deal of observation and study.

If you should turn a 2- or 3-inch telescope, carefully
equipped with a darkened lens, upon the sun almost any
day within the next few years, you might see a few sunspots
scattered upon its bright yellow surface between 5 and 40
north and south latitude. They are often grouped in pairs
and clusters and seem to move across the disk as the sun
turns on its axis. Some last during a full rotation (25 days);
a few stay longer, but most have only a few days' existence.

On careful examination these spots would be seen to con-
sist of a dark center surrounded by a lighter area. Although
they look so tiny in a small telescope, many of them are really
large enough to engulf the earth, and some have been known
to reach the size of 150,000 miles in diameter. Another strange
thing about these spots is that they appear black when in
reality they are white hot.

When one turns a telescope on the sun, one does not always
see only full-grown spots, for new magnetic storms are whirling
up on the sun as old ones die down. New sunspots may first
be detected in the process of formation as small black patches
on the visible disk of the sun; or they may start to form on the
side that is turned away from the earth, and then they will
first be noticed as they round the edge of the sun. In this
case they are marked by the bright patches called "faculae"
which surround them. The faculae are seen best on the limb

Solar Observations 75

of the sun, and they can rarely be seen at the center of the
sun's disk.

There are two general methods of observing these spots
with the help of a telescope. One is by observing directly
through the telescope, but extreme care must be taken to use
a sun glass or ray filter.

A second way is by allowing the enlarged image to fall
on a piece of paper held at the eye end of the telescope. Rack
out the eyepiece a little farther than for normal visual observa-
tion. Then move the paper until the image is well projected
and sharp. A wire frame can be made to hold it at the correct
distance (see page 95). This leaves you free to chart the
position of the spots by tracing them as they appear on the
paper. It is a good idea to place a black cloth over the wire
framework to keep out some of the extraneous light and thus
make the image more distinct. A piece of cardboard with a
hole in the center, placed on the telescope tube near the
rack and pinion, also helps to keep out light. The advantages
of this method are that it eliminates danger to the eyes, per-
mits simultaneous observation by a number of observers, and
facilitates charting.

And, lastly, some people use a solar eyepiece, equipped
with a prism that diverts most of the sunlight and permits a
direct view of the sun with the least chance of danger to the
eyes. But even with this "Herschel solar prism" a colored
sun glass is needed.

At times with even a 2-inch telescope, faculae may be seen
in association with the spots. These are lighter areas above
the sun's surface, which become more easily visible the nearer
they are to the sun's limb.

Besides charting the spots there are other statistics thac
can be gathered concerning them, such as number, speed of
rotation, and duration. From your chart you can, of course,
get position and grouping. The size, too, is easy to determine.
Let the diameter of the sun's image, 4 inches, for example,
represent the diameter of the real sun 864,000 miles. If the
spot's image is Ke inch in diameter (that is, one sixty-fourth

76 Handbook of the Heavens

of the sun's image), it will be one sixty-fourth of the sun's
actual diameter or 13,500 miles. This is an average spot!

Even if you do not have a telescope, you can make observa-
tions of the sun, noting the rising and setting points on the
horizon and the time of sunrise and sunset over a period of
several months. They are dependent both upon the time
of year and upon the latitude of the place and they follow
definite laws. They affect the "insolation, " or amount of sun's
rays received and are seasonal variations.

As seen from northern latitudes, at the time of the winter
solstice the setting sun is as far south on the horizon as it can
get. Day by day it gradually moves northward on the horizon
until the time of the summer solstice in June. If you were at
the equator, you would find that on December 21 the sun
would rise at 6 A.M. about 23^ south of the east point on the
horizon and set at 6 P.M. 23^ south of the west point. In
our latitudes, 40 north, it rises about 7:30 A.M. 32 south of
the east point, on December 21, and sets about 4 130, 32 south
of the west point. But at Oslo, Norway, the sun rises about
2:45 A.M. on June 21, at a point 54 north of the east point
on the horizon, and does not set until 9:15 P.M. Places with
such high latitudes therefore have much more sunlight during
the summer months. Above the Arctic Circle, from May until
July, it is light almost all the time, but from November to
January it is dark nearly all the time. Indeed, all latitudes on
the earth's surface have definite times and places for the rising
and setting of the sun.

Solar eclipses, although rare for any one section of the
earth's surface, have completely captured the layman's fancy
and he will travel miles to see one. During the total eclipse
of August, 1932, New England was crowded with tourists from
all over the United States indeed from all over the world.

Those travelers who were not " clouded out" felt well
rewarded for their efforts. If you have ever seen the moon
slowly creep across the face of the sun, steadily covering more
and more of it until at last the brilliant sphere disappears and
the corona suddenly flashes into view, you will understand why.

Solar Observations

Yerkes Observatory

SUN'S DISK WITH SPOTS. A
photograph of a portion of the solar sur- .
face, showing great groups of sunspots.
The dark umbra of each is visible, and
the surrounding penumbra as well as
the lighter faculae near the edge.

James Clark, AMNH

SOLAR ECLIPSE. A beautiful
photograph of the sun's corona, taken
during the solar eclipse of August 31,
1932. The equatorial streamers reach a
quarter million miles from the solar sur-
face. (From a motion picture.)

But the corona, beautiful as it is, is not the only phe-
nomenon visible. The prominences, huge masses of flaming
gas thrown out to heights of thousands and hundreds of
thousands of miles by eruptions inside the sun, are well worth
observing.

The Baily's beads and the "diamond-ring" effect, two
other impressive displays seen during a total eclipse, are not,
like the corona and prominences, actual parts of the sun which
the eclipse makes visible. They are merely lighting effects.
Just before the moon, moving across the face of the sun,
shuts off the last tiny crescent of light, a few rays shine
through the valleys along the edge of the moon. The result is
one or several lighted dots along the dark rim of the satellite
the Baily's beads.

Then, just as the beads vanish, the sun's lower atmosphere,
the inner corona, comes into view shining brilliantly. At
nearly the same instant the pearly outer corona flashes forth.
Along the black rim of the moon the reddish prominences lace
into the inner corona. But almost as soon as it can be seen, the
glorious spectacle has begun to fade.

78 Handbook of the Heavens

Just before the sun reappears, its outer corona is blotted
out, but the inner corona remains for half a minute as a yellow
ring around the sun. When the first speck of-the sun returns
to view, irradiation makes it seem much larger than it really
is, and the total effect is the formation of a diamond ring with
the speck of the sun as the diamond and the inner corona as
the ring.

The eclipse also has its visible effects on the earth. During
the whole time that the moon is creeping toward its central
position and away from it, the light shining through the small
spaces between tree leaves and through small holes, instead
of forming the usual disks on the ground, makes tiny crescents
images of the disappearing sun.

Then, about ten minutes before totality, an eerie darkness
begins to be felt. Chickens and other animals become alarmed
and the air gets noticeably colder. Shortly before the shadow
reaches the observer, rippling shadow bands appear on all
light surfaces, and (from the high vantage point of an airplane
or even a high hill) the moon's shadow itself can be seen
advancing. Finally the moon covers the sun completely, the
corona streams out, and the brighter stars and planets are
visible.

During a partial eclipse, when the moon is seen moving
across the face of the sun although it does not cover it entirely,
there are comparatively few observations that an amateur
can make. He can time "first contact," when the moon
first nicks the edge of the sun, and he can time the last contact
(there are only two in a partial eclipse), when the moon
finally moves off the face of the sun. At intervals during the
eclipse he can estimate the percentage of the surface covered
and measure the drop in temperature.

He can also make note of the crescents cast upon light
surfaces when the sunlight shines through leaves or small
holes. But there is little else that can be attempted during
a partial eclipse.

The total eclipse, of course, provides a better opportunity
for the observer. He can record all the phenomena mentioned

Solar Observations 79

above the corona, prominences, Baily's beads, diamond
ring, temperature drop, effect on animals, shadow bands, etc.
He can time four contacts: first, when the moon first touches
the sun; second, the instant of beginning of totality; third, the
instant at which totality ends; fourth, the moment when th,e
moon moves off the face of the sun. He can count and identify
the stars that appear during totality.

If he is equipped with a direct-vision spectroscope, he may
watch for the reversal of the spectrum lines from dark to
light and light to dark as the flash spectrum of the " reversing"
layer becomes visible just before and after totality.

In observing the corona, prominences, and similar phe-
nomena, note their shape and position. In the case of Rally's
beads, count the number seen; with the shadow bands,
measure th


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