Spendours of the sky

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M.LEV

THE 26-INCH EQUATORIAL OF THE UNITED STATES NAVAL

OBSERVATORY WITH WHICH THE SATELLITES OF MARS WERE

DISCOVERED IN 1877

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Splendours of the Sky

BY

ISABEL MARTIN LEWIS, A.M.

(Connected with the Nautical Almanac O$G9

ofthtU.S.

LONDON
JOHN MURRAY

ALBEMARLE STREET, W.
1920

Copyright. 1919; by
DUFFIELD AND COMPANY

Printed in the U.S. A.

CONTENTS

CHAPTER PAGE

I. VASSALS OF THE SUN i

II. THE ORIGIN OF THE SOLAR SYSTEM . 10

III. EVASIVE MERCURY . ,_» , 17

IV. VENUS, EARTH'S SISTER PLANET . . 24
V. How OLD Is MOTHER EARTH? ., . . 31

VI. MYSTERIES OF MARS . . . .,«,.. 39

VII. THE ASTEROIDS 46

VIII. THE PLANETS JUPITER AND SATURN COM-
PARED 53

IX. SATURN THE RINGED PLANET .... 61

X. PLAIN FACTS ABOUT THE MOON ... 66

XI. SOME UNSOLVED PROBLEMS OF THE MOON 74

XII. SHOOTING STARS AND METEORS ... 82

XIII. OUR CELESTIAL VISITORS, COMETS . . 91

XIV. How CARBON DIOXIDE IN THE EARTH'S

ATMOSPHERE AFFECTS CLIMATE . . 98
XV. How A LITTLE SPECTROSCOPE TELLS THE

SECRET OF LIGHT v 106

XVI. SECRETS OF THE SUN REVEALED BY THE

SPECTROSCOPE 115

XVII. THE SPOTS ON THE SUN 124

XVIII. SOLAR EXPLOSIONS 132

XIX. SOME RECENT ECLIPSES — THEIR VALUE

TO ASTRONOMY 140

XX. ARE THERE OTHER PLANET WORLDS? . 157

XXL DRIFT OF THE STAR STREAMS .... 165

XXII. THE MILKY WAY 172

XXIII. Do DARK STARS EXIST IN THE HEAVENS? 179

XXIV. THE BRILLIANT NOVA OF 1918, NOVA

AQUIL^E No. 3 186

PREFACE

THE following book has been compiled from a
series of articles written by the author during the
past three years for * ' The New York Evening Sun ' '
upon astronomical subjects of general, popular
interest^.

Requests from a number of readers for copies of
these articles have led to the publication of a
selection and arrangement of them, including some
revisions and changes, which form a connected and
comprehensive treatment of the astronomy of the
present day.

Diagrams, formulae and mathematical proofs
have been entirely omitted as unsuitable to a
popular treatment of the subject. It is not the
desire of the author to attempt to enter into a
detailed scientific exposition of astronomical truths,
but simply to tell in non-technical terms something
about the wonderful progress tfe# astronomers are
now making in delving into the mysteries of time
and space , and in solving problems concerning the
heavenly bodies that a few years ago appeared to be
beyond solution.

CHAPTER I

VASSALS OP THE SUN

TTTHO has not admired the brilliant and beau-
tiful planets, members of our own solar
system — glorious Venus, fiery Mars, ringed Saturn
and magnificent Jupiter ? Possibly some of us have
also spied in the twilight hour following sunset
or preceding sunrise elusive Mercury, closest at-
tendant of the sun.

From remotest antiquity these five planets have
been observed apparently wandering among the
fixed stars, though in truth separated from them
by inconceivable immensities of space. Eight plan-
ets in all, including our own little planet earth,
with their attendant moons, unceasingly encircle
the sun in obedience to the universal and myste-
rious law of gravitation. To modern astronomers
we owe the discovery of the two outermost planets,

s

SPLENDORS OF THE SKY

Uranus, just at the limit of visibility of the un-
aided eye, and Neptune, barely showing in small
telescopes the planetary disk that distinguishes it
from the fixed stars far beyond.

Of the nearer planets, Mercury is by far the
most difficult to observe, for it is lost in the solar
rays most of the time. In less than three months,
eighty-eight days to be exact, Mercury completes
one trip around the sun. During a considerable
portion of this time the planet is either hidden be-
hind the sun or passing between us and the sun.
It is only when farthest to the east or west of the
sun, at elongations, that it is observable. As Mer-
cury can never depart more than twenty-eight de-
grees from the sun, even under the most favorable
circumstances, it usually escapes detection. At
eastern elongations Mercury sets after the sun and
is evening star. At western elongations it may be
seen in the twilight hours just preceding sunrise as
morning star, and when found delights us by ap-
pearing as a beautiful star about as bright as bril-
liant Vega. Mercury is the nearest to the sun of all
the planets, also the smallest, the hottest and the
fleetest. Its orbit departs more from the circular
shape than does the orbit of any other planet, so that

2

SPLENDORS OF THE SKY

the planet's distance from the sun varies as much
as fifteen million miles. The diameter of Mercury
is only three thousand miles and both Jupiter and
Saturn have satellites that surpass Mercury in size.
It is almost a certainty that Mercury always turns
the same face toward the sun. The temperature,
therefore, is torrid on one side, frigid on the other,
and the temperature differences are made all the
more extreme from the fact that Mercury has no
atmosphere, probably, as is the case with the moon,
because it has not sufficient gravitational force to
hold one.

In Venus we behold our sister planet. The
diameter of this planet is about two hundred miles
less than that of our own planet. Venus far sur-
passes all the other planets in brilliancy, even Jupi-
ter, the giant among them all, cannot rival her in
splendor. This is due to the fact that she is nearer
to us than any other planet, at nearest approach
only 26,000,000 miles away. In strong contrast
to Mercury, Venus is surrounded by a dense atmos-
phere. The surface of the planet is hidden by
clouds and no surface markings can be distin-
guished with certainty, and so it is still undecided
whether Venus rotates on its axis in a day about

3

SPLENDORS OF THE SKY

never allowed to take form, due to the disruptive
effect of Jupiter's mighty mass.

The major planets are distinguished from the
terrestrial group by their great size, enormous dis-
tances from the sun and extremely low density,
not much exceeding that of water — in the case of
Saturn even less. The density of the terrestrial
group is extremely high. Our own planet, which
possesses the highest density of all the planets, has
5.5 times the density of water.

This low density of the outer planets implies
they are still mostly in a gaseous condition.

Jupiter, the largest of the planets, has a mass
two and one half times as great as all the other
planets combined. He is also the centre of a large
satellite system of nine moons, two of which
surpass the planet Mercury in size. Four of these
moons have been known from the days of Galileo
and can be observed even with an opera glass.

Saturn, next beyond Jupiter, is noted for its
wonderful system of concentric rings, composed of
countless tiny moonlets, and its large satellite fam-
ily of nine moons. Titan, the largest, has a diam-
eter of 3,500 miles, which places it between Mer-
cury and Mars in size. Saturn is also remarkable

6

SPLENDORS OF THE SKY

for the fact that its density is less than water. It
is the only planet in the solar systems that would
float in water.

It is almost impossible for the human mind to
grasp the immensity of this solar system of ours
and realize as well that even the solar system is
but one of millions of systems that form the stellar
universe.

If we should try to represent our solar system to
scale and should choose for the sun a globe two and
a half feet in diameter, Jupiter would be a ball
three inches in diameter. Saturn would be a little
over two and a half inches in diameter, Uranus and
Neptune balls of nearly equal size, a little more
than one inch in diameter, Uranus exceeding Nep-
rtme in diameter by about one-tenth of an inch,
while the terrestrial group would appear insignifi-
cant beside these larger members of our system.
Venus and our own Earth on this scale would be
but one-quarter of an inch in diameter, while Mars
and Mercury would have diameters one-seventh and
one-tenth of an inch respectively. Placed at the
distance of the nearest star our largest telescopes
would fail to reveal the existence of Jupiter, the
largest of all tbe planets.

7

SPLENDORS OF THE SKY

To form some idea of the relative distances of
the planets from the sun, let us consider the time
that it takes a ray of sunlight to reach each of the
planetary orbits travelling outward from the sun
at a speed of 186,000 miles per second. Three min-
utes after leaving the sun it crosses the orbit of
Mercury, at the end of six minutes it passes the
orbit of Venus, eight and a fraction minutes it
requires to reach the earth's orbit, and nearly
thirteen minutes after leaving the sun it arrives at
the orbit of Mars. Darting into the vast abyss
lying beyond Mars' orbit, it travels fully thirty
minutes longer before it comes to the orbit of Jupi-
ter. Thirty-six more minutes pass before it comes
to Saturn's orbit. It takes more than two and a
half hours for this ray of sunlight to travel from
the sun to the orbit of Uranus. More than four
hours after the time it started it finally comes to
the orbit of Neptune at a distance of nearly 2,800,-
000,000 miles from the sun. From here it speeds
onward to the stars beyond and reaches the nearest
in four and a half years.

The periods of revolution of the planets around
the sun differ as widely as their masses and dis-
tances from the sun. In eighty-eight days Mer-

8

SPLENDORS OF THE SKY

cury completes its rapid journey. Venus requires
seven and one-half months, Mars six hundred and
eighty-seven days. Twelve years pass by, however,
before Jupiter makes one trip around the sun. Sat-
urn requires twenty-nine and one-half years, Ur-
anus eighty-four years, and nearly one hundred and
sixty-five years elapse before Neptune sweeps en-
tirely around his mighty path through the heavens.

CHAPTER II

THE ORIGIN OF THE SOLAE SYSTEM

the material of which the sun and plan-
ets are fashioned originally existed in the
form of a nebulous mass practically all astrono-
mers believe; but the process by which our solar
system developed from a chaotic nebula into an
orderly and well-regulated family of planets re-
volving around a central sun is one of the fascinat-
ing and puzzling problems of astronomy.

Near the end of the eighteenth century the fam-
ous mathematician and astronomer La Place, ad-
vanced his noted nebular hypothesis of the origin
of the solar system which gained universal ac-
ceptance almost immediately and held undisputed
sway for nearly an entire century. Modifications
and changes had to be made at times, however, to
adapt the theory to later discoveries, and finally in
10

SPLENDORS OF THE SKY

the light of more recent researches an almost com-
plete abandonment of the theory has resulted.

According to the nebular hypothesis, a vast gas-
eous nebula originally extended beyond the present
orbit of the outermost planet, Neptune, and slowly
rotated in the direction in which the planets now
revolve around the sun. Such a great mass would
lose heat by radiation into space and would con-
tract. As the rotating mass contracted it would
of necessity rotate faster and faster, and as a re-
sult equatorial rings of nebulous matter would be
abandoned, which would have a tendency to break
unless perfectly uniform and circular. Excess of
material at any one point in the ring would draw
to itself the remaining material in the ring. The
result would be the formation of a planet which
would continue to revolve around the central con-
tracting nebula at the distance at which the ring
was abandoned. Other rings left behind at vari-
ous stages as the central nebulous mass continued
to contract, would form additional planets. The
globular masses formed when the abandoned rings
broke up might, in the same manner, contract and
leave behind rings which would go to form the
satellites by which most of the planets are at-

11

SPLENDORS OF THE SKY

tended. The rings of Saturn were supposed to be
rings abandoned by the contracting mass of that
planet, which, for some reason, had kept their orig-
inal form. The earth, according to the nebular
hypothesis, was once in a gaseous condition and
gradually cooled down to its present form of sur-
face crust and molten interior. The theory of La
Place was in accord with all the facts then known
concerning the solar sj^stem. It seemed to explain
satisfactorily why the planets move in orbits that
are almost perfect circles and why they all turn
on their axes and revolve around the sun in the
same direction, namely from west to east, and also
why they all revolve around the sun in nearly the
same plane.

The asteroids or planetoids, however, furnish
notable exceptions to these laws. At the time La
Place advanced his theory they had not been dis-
covered. These small members of our systems are
now numbered by hundreds. The diameter of the
largest does not exceed five hundred miles, and
most of them are much smaller. Their orbits lie
between the orbits of Mars and Jupiter and are
remarkably different from the orbits of the major
planets, for they vary in shape from almost per-
12

SPLENDORS OF THE SKY

feet circles to ellipses as elongated as some comet-
aiy orbits. Instead of lying in nearly the
same plane as is the case with the major planets,
they intersect the common plane at all angles from
zero to thirty-five degrees, and could, therefore,
never have been formed from an abandoned ring
of the contracting solar nebula.

Moreover, it has been discovered that certain
satellites of the outer planets do not share the com-
mon direction of revolution of the planets from
west to east, but move in a retrograde motion
around their primaries from east to west. Also,
according to the nebular hypothesis, no satellite
could revolve around its primary in less time than
its primary takes to turn on its axis; but Phobos,
the inner satellite of Mars, finishes three revolu-
tions and starts on a fourth before Mars has turned
once on its axis. The moonlets composing the inner
ring of Saturn also complete circuits in between
five and six hours, although Saturn requires ten
and a half hours to rotate on its axis. Other in-
stances might be cited to show the failure of the
nebular hypothesis to explain all the facts now
known concerning our solar system. This noted
hypothesis served as a good working hypothesis in

SPLENDORS OF THE SKY

its day, nevertheless, and greatly stimulated inves-
tigations in the allied sciences of geology, zoology
and biology in the nineteenth century. It is far
easier to tear down a theory than to build up a new
one that will fit in with all the observed facts. Sev-
eral new theories of the origin of the solar system
have been advanced, but no one theory seems satis-
factory in all respects. Astronomical discoveries
of recent years have shown our solar system to be. a
more complicated mechanism than was at first sus-
pected.

The idea that the nebula from which the solar
system was evolved was originally spiral in form
is now quite generally held. Chamberlin and
Moulton have developed a theory of the origin of
the solar system along these lines, known as the
Planetesimal Theory. It can be shown that a spiral
nebula might arise through the close approach of
two stars, or from the approach of two nebulous
streams and their curling together by mutual at-
traction, or by the curling up of a single nebulous
stream, due to its own gravitation. There are
probably close to two billion luminous stars in our
stellar system, all in motion, and we can reasonably
assume that collisions or close approaches will oc-

14

SPLENDORS OF THE SKY

cur despite the fact that enormous distances sepa-
rate the stars from one another. When we admit,
as actual discovery forces us to, the existence of
dark stars and dark star systems and dark nebu-
lous matter, as well as bright, the likelihood of oc-
casional collisions or close approaches increases. It
has also been found that the nebula from which a
solar system evolves need not necessarily be gas-
eous or at high temperature, since a nebulous
swarm of meteoric particles would act in the same|
way as the molecules of gas in a gaseous nebula.

In favor of the belief that the original solar neb-
ula was spiral in form, it can be shown that, while
no nebula of the form required by the nebular hy-
pothesis of La Place is known to exist, the spiral
form of nebula abounds throughout the universe.
Even the stellar universe itself may consist of stars
streaming in obedience to the laws governing a
spiral formation. Although we are still uncertain
as to the exact manner of the evolution of
our solar system from the primitive nebula, proofs
of the fact that suns evolve from nebulae and pass
through all the stages from youth to old age are
written in the heavens themselves. A careful sur-
vey of the heavens shows stars not yet freed of

15

SPLENDORS OF THE SKY

its day, nevertheless, and greatly stimulated inves-
tigations in the allied sciences of geology, zoology
and biology in the nineteenth century. It is far
easier to tear down a theory than to build up a new
one that will fit in with all the observed facts. Sev-
eral new theories of the origin of the solar system
have been advanced, but no one theory seems satis-
factory in all respects. Astronomical discoveries
of recent years have shown our solar system to be a
more complicated mechanism than was at first sus-
pected.

The idea that the nebula from which the solar
system was evolved was originally spiral in form
is now quite generally held. Chamberlin and
Moulton have developed a theory of the origin of
the solar system along these lines, known as the
Planetesimal Theory. It can be shown that a spiral
nebula might arise through the close approach of
two stars, or from the approach of two nebulous
streams and their curling together by mutual at-
traction, or by the curling up of a single nebulous
stream, due to its own gravitation. There are
probably close to two billion luminous stars in our
stellar system, all in motion, and we can reasonably
assume that collisions or close approaches will oc-

14

SPLENDORS OF THE SKY

cur despite the fact that enormous distances sepa-
rate the stars from one another. When we admit,
as actual discovery forces us to, the existence of
dark stars and dark star systems and dark nebu-
lous matter, as well as bright, the likelihood of oc-
casional collisions or close approaches increases. It
has also been found that the nebula from which a
solar system evolves need not necessarily be gas-
eous or at high temperature, since a nebulous
swarm of meteoric particles would act in the same|
way as the molecules of gas in a gaseous nebula.

In favor of the belief that the original solar neb-
ula was spiral in form, it can be shown that, while
no nebula of the form required by the nebular hy-
pothesis of La Place is known to exist, the spiral
form of nebula abounds throughout the universe.
Even the stellar universe itself may consist of stars
streaming in obedience to the laws governing a
spiral formation. Although we are still uncertain
as to the exact manner of the evolution of
our solar system from the primitive nebula, proofs
of the fact that suns evolve from nebulae and pass
through all the stages from youth to old age are
written in the heavens themselves. A careful sur-
vey of the heavens shows stars not yet freed of

15

SPLENDORS OF THE SKY

their nebulous appendages, and even whole clusters
of stars wrapped in nebulous matter. All stages
of evolution are represented from the blue stars of
youth to the feebly flickering red stars of old age
and the cold, dark stars that have lived their lives
and speed onward through space until the time
comes, when they may start perchance, upon a new
life, through some celestial catastrophe.

16

CHAPTER III

EVASIVE MERCURY

Tl .TERCURY is the most difficult to observe of
*•**• all the satellites of the sun, because it never
departs more than twenty-eight degrees from its
ruler, even under the most favorable circumstances,
and is usually entirely concealed by the blinding
rays of the sun.

Spring is the best time to view this planet as
evening star, and autumn the most favorable time
to search for it as morning star, since the ecliptic,
the path of the sun, near which the moon and the
planets are always to be found, then rises most
sharply along the horizon.

Mercury can only be seen for about two weeks at
a time near the dates of its elongations. The planet
is, of course, found with great difficulty in high
latitudes and is rarely seen in northern Europe.

17

SPLENDORS OF THE SKY

In fact, comparatively few people have ever seen
this closest attendant of the sun. Copernicus, so
we are told, never saw it.

When seen at time of elongation, near the hori-
zon, Mercury usually has a slightly reddish tinge,
due to the fact that its rays are travelling through
the denser lower strata of the atmosphere. It will
also appear to twinkle somewhat for the same rea-
son. Mercury is, in fact, sometimes referred to as
"the twinkler."

All the other planets shine with calm, steady
light, and it is interesting to compare Mercury, if
it can be found, with the other bright planets when
they are visible at the same time.

Most astronomical observations of Mercury are
made in full daylight by screening off the light of
the sun. Sunlight is less disturbing to observations
made with large telescopes than the dense haze of
sunset and sunrise skies. It is due largely to the
difficulties of observing this planet that the period
of its rotation on its axis and, therefore, the length
of its day and night has not been settled beyond
question.

It is virtually certain, though, that the planet's
rotation period is equal to the period of its revolu-

18

SPLENDORS OF THE SKY

tion around the sun, or eighty-eight days, and that
it always keeps the same face turned toward the
sun. If this is the case there are two longitudinal
zones on the planet's surface forty-seven degrees
in width that experience a rising and setting of the
sun and have forty-four days of light, followed by
an equal period of darkness. This is due to the
great ellipticity of the planet's orbit, which departs
more from a circular form than that of any other
planet in the solar system.

The planet's rate of rotation on its axis is uni-
form, but its rate of revolution around the sun,
due to the high eccentricity of its orbit, varies from
thirty-six miles a second at perihelion to twenty-
three miles a second at aphelion. So there are
times when Mercury falls behind its mean position
by as much as twenty-three and one-half degrees,
and times when it darts ahead of its mean position
by an equal amount.

As a result the sun's rays fall first twenty-three
and one-half degrees beyond the point on the plan-
et's surface where they would fall if the orbit were
circular, and then twenty-three and one-half de-
grees short of this position. This gives rise to the
two zones forty-seven degrees wide and diametric-

19

SPLENDORS OF THE SKY

ally opposite each, other that have an alternate day
and night, each equal in length to forty-four ter-
restrial days. Between these two lie the two zones,
each one hundred and thirty-three degrees wide,
one of perpetual day and the other of perpetual
night.

On the daylight side of the planet the sun ap-
pears to oscillate backward and forward through
an angle of forty-seven degrees, and the lowest tem-
perature is higher than that of the boiling point
of water upon the earth. Upon the night side the
only light is that furnished by the stars that shine
with a radiance and glory unknown to us who dwell
in a world that is always surrounded by a dense,
obscuring atmosphere. Mercury has no appreci-
able atmosphere and the terrible cold of space pre-
vailing upon the night side of the planet is un-
tempered by warm air currents, such as would flow
from the hot to the cold side if the planet possessed
an atmosphere.

Here exists a world of extremes, scorched
on one side, frozen on the other, while in
the zones of alternate day and night that lie
between is to be found all the range of temper-
ature that lies between the two extremes. Lack of

20

SPLENDORS OF THE SKY

atmosphere on Mercury prohibits the existence of
life.

The planet reflects about fourteen per cent, of
the sunlight it receives, which is slightly less than
the amount reflected by the moon's surface and it
is believed that its surface resembles that of our
satellite in being barren and mountainous.

The axis of the planet is probably perpendicular
to its orbit, and it has, for this reason, no seasons,
though its greatly varying distance from the sun
produces the same effect. The average distance of
the planet from the sun is 36,000,000 miles. At
perihelion its distance is 7,500,000 miles less than
this amount and at aphelion 7,500,000 miles greater.
The heat and light received from the sun while in
these two positions vary in the ratio of nine to
four. A marked increase in the apparent size of
the sun would be noticed in passing from aphelion
to perihelion and a corresponding decrease in pass-
ing from perihelion back to aphelion.

Mercury is not only the smallest of all the plan-
ets, but it is even surpassed in size by Titan, one
of the satellites of Saturn and Ganymede, the third
satellite of Jupiter.

The fact that the perihelion of Mercury moves
21

SPLENDORS OF THE SKY

faster than it would move if acted upon only by
known laws has long been a subject for astronomi-
cal investigation, and many theories have been ad-
vanced in explanation, among them the theory of
the existence of an intra-mercurial planet. Ac«
cording to Leverrier, the noted French mathema-
tician, the mass of such a planet would need to be
one-half the mass of Mercury itself in order to ac-
count for the actual discrepancy existing between
the observed and computed values.

It is virtually certain as a result of careful ex-
amination of many photographs taken at the time
of total eclipses of the sun that no object exists
within the orbit of Mercury with a diameter ex-
ceeding thirty or forty miles. There is the possi-
bility that a number of minute bodies of asteroidal
size may revolve around the sun within the orbit
of Mercury, but it is very improbable that their
combined mass would total half the mass of Mer-
cury.

So we may assume that Mercury enjoys the
distinction of being the smallest of all the plan-
ets, and also the nearest to the sun. It is, in fact,
distinctive in many ways. Its orbit is the most
elliptical and the most highly inclined to the eclip-

SPLENDORS OF THE SKY

tic of all the planetary orbits. The planet itself
is the most rarely seen of all planets visible to the
naked eye, and the only one that does not possess
an atmosphere.

23

CHAPTER IV

VENUS, EARTH'S SISTER PLANET

THE silvery radiance of Earth's sister planet,
Venus, attracts the attention of all whenever
she appears in the western sky, since she is then
the most beautiful and conspicuous stellar object
in the heavens. Though fully as beautiful when
she is visible as "morning star" before sunrise,
few of us are up at that time to admire her.

Half way between the horizon and the zenith
marks the limit of her departure from the sun.
Since the orbit of Venus lies between us and the
sun we may never see her in opposition to the sun
or upon the meridian at midnight, as we do the
outer planets, Mars, Jupiter and Saturn, and, un-
like these planets, Venus does not show a circular
disk in the telescope, but exhibits all the phases
of the moon and when at her greatest brilliancy

24

SPLENDORS OF THE SKY

appears like a crescent moon in the telescope.
Although Venus approaches nearer the earth
than any other celestial body except the moon, the
asteroid Eros, and a chance comet, she is, unfortu-
nately, entirely invisible at the time of closest ap-
proach. The phase she then exhibits corresponds
to that of new moon. Her illuminated face is
turned toward the sun, her night side toward the
earth. She is then but 26,000,000 miles away and
between the earth and sun. Just before and after
this time, which is spoken of as the time of inferior
conjunction, she appears as a very thin crescent
in the telescope, resembling the moon a day or two
before and after new moon. Near the time of
nearest approach of the two planets some astrono-
mers have observed a faint, ashy light upon the
darkened disk of the planet. As Venus has no sat-
ellite, this cannot be attributed to reflected moon-
light, though some have believed it to be due to
earth shine or the light from our own planet re-
flected from the surface of Venus. It is extremely
doubtful that earth shine could be appreciable
when a distance of fully 26,000,000 miles separates
the two bodies, though our planet presents to
Venus at this time the phase of the full moon and

25

SPLENDORS OF THE SKY

appears much larger and more brilliant to Venus
than Venus ever does to us. That it may be due
to some electrical manifestation in the planet's at-
mosphere similar to auroral displays in our own
seems more reasonable. It is also near the time of
closest approach that a very faint ring of light may
be observed outlining the disk of the planet. This
is caused by the reflected sunlight from the dense
atmosphere that surrounds the planet and fur-
nishes one of many proofs of the existence of such
an atmosphere.

If higher forms of life exist upon our sister
planet and dense clouds do not always completely
hide the heavens, we may imagine with what in-
terest our own little earth-moon system would be
observed at this time of closest approach of the two
bodies. A most beautiful and interesting double
star our earth-moon system must appear from
Venus. Our satellite, of course, would be plainly
visible to the naked eye from Venus and its con-
stantly varying positions with reference to our
planet would soon reveal the fact that it is in rev-
olution around the earth. How intelligent beings
there might puzzle over the earth's continents and
seas, changing vegetation, polar snow caps, clouds,

26

SPLENDORS OF THE SKY

daily rotation and sensational changes ! Just as we
puzzle over Mars and its baffling surface markings
may not another world be puzzling over our pe-
culiarities? This may be most unlikely, but it is
a possibility. About the planet Venus we know
very little except that its age may be very nearly
that of our own planet and that it is more suited to
the development of forms of life such as we have
upon the earth than any other planet in the sun's
family, provided it rotates upon its axis once in
about twenty-four hours. Upon this point we are
still in doubt, for observations of Venus are always
made at a disadvantage, owing to the density of its
atmosphere and the fact that it is always more or
less unfavorably situated for observation.

Many markings have been observed upon Venus,
but, unfortunately, they do not appear the same
to all observers, and it is still impossible to say
with certainty whether the actual surface of the
planet or cloud formations are seen. Even deter-
minations of the planet's period of rotation by
means of the spectroscope contradict each other
flatly. After years of observations we do not yet
know whether Venus rotates on its axis in twenty-
four hours or in two hundred and twenty-five days,

37

SPLENDORS OF THE SKY

the period of its revolution around the sun. In
the latter case it would always turn the same face
toward the sun just as our satellite always turns
the same face toward the earth. If this state of
affairs exists on Venus one side never sees the sun,
the other side never sees the heavens studded with
myriads of stars, but feels the torrid heat of a
sun immovable in the sky, possibly screened from
view by friendly clouds. The planet 's dense atmos-
phere would tend to mitigate the two extremes of
temperature found on opposite sides of the planet
by a constant flow of air currents between the two
sides. In fact, there would be, under such circum-
stances, storms of frightful intensity continually
raging over the planet's surface. If, on the other
hand, Venus turns on its axis in approximately
twenty-four hours no other planet in the solar sys-
tem so closely resembles the earth.

The diameters of the two planets differ by about
200 miles, and in mass, density and surface gravity
they are nearly the same. A man weighing 170
pounds upon the earth would weigh 145 pounds
upon Venus. We could move about a little more
easily upon Venus than we do upon our own planet.
We would probably find the atmosphere very much

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SPLENDORS OF THE SKY

the same. The reflecting power of the atmosphere
of Venus is very nearly the same as that of the
thunder heads we often observe in our summer
skies, which seems to indicate a cloud laden at-
mosphere for our sister planet. Though some ob-
servers have placed the density of the atmosphere
of Venus at twice the density of the earth 's at-
mosphere, others believe they are virtually the
same. It is in the amount of light and heat re-
ceived from the sun that we note the greatest
difference between the two planets. Venus receives
nearly twice as much light and heat from the sun
as we do. This may seem to us a rather uncomfort-
able amount, and we wonder how the inhabitants
stand it, but possibly they may wonder how we
exist upon a planet that is so poorly lighted and so
cold. Upon our own planet we find life flourishing
under conditions of great diversity. Countless
forms of life exist under the sea and upon the
surface of our planet, in the torrid heat of the
tropics and the frigid cold of the polar regions.
So life upon Venus does not seem so improbable
unless it shall be determined eventually that the
planet always keeps the same face turned toward
the sun. In case it shall be found that Venus

29

SPLENDORS OF THE SKY

rotates on its axis once in about twenty-four hours
we can hardly escape the conclusion that the life
process must be running its course there as well as
here. Given all the essentials for the development
of life, — air and water, heat and light in abund-
ance,— it seems almost too much to assume that such
a world is devoid of life.

30

CHAPTER V

HOW OLD IS MOTHER EARTH?

THE age of Mother Earth is a perplexing ques-
tion, not only for astronomers but for geol-
ogists and biologists as well.

There are many different methods of attacking
the problem, but all agree that the long series of
evolutionary changes that have taken place upon
our planet could not have been brought about in
any period of time less than tens of millions of
years. This applies, moreover, simply to the dur-
ation of the life process upon the earth and does not
include the ages that must have elapsed from the
earth's beginning to the time when it was in a con-
dition suitable for the production of life.

Geologists and biologists find their evidence of
the earth's age in the condition of its crust, in the
stratification of its rocks and the fossil remains of

31

SPLENDORS OF THE SKY

various forms of life formerly existing upon it,
while for the astronomer the solution of the prob-
lem is dependent upon how long the sun's light and
heat have been supplied at the present rate. Bar-
ring outside interference, such as the close approach
of a passing sun, the duration of life within the
solar system depends entirely upon how long the
sun's supply of radiant energy can be maintained.

Considering, first, the evidence furnished by the
biologist for the duration of life upon our planet,
through examination of fossil remains in rocks of
different geological formations, it has been found
that the earliest and most primitive forms of life
appeared in rocks of earliest formation and a chain
of increasingly higher and higher forms of life ap-
peared as the age of the geological formations de-
creased. In rocks of the latest formation the fossil
remains of the highest forms of life appeared.
Noted biologists have placed the period necessary
for this excessively slow process of evolution as high
as two billions of years, and though some feel this
is too high, none can see how such a long chain of
evolution could have been completed in less than
some hundreds of millions of years.

The time required for the disintegration of the
32

SPLENDORS OF THE SKY

original earth material, its deposition on the bot-
tom of lakes and oceans, stratification and the num-
berless repetitions of the process that are known
to have taken place could not be less than one
hundred millions of years, according to the most
conservative estimates of geologists.

Another geological method of determining the
age of the arth is to compute the time required for
the oceans to acquire their present salinity. Since
the rivers carry to the oceans various salts in sol-
ution and the water evaporated from the oceans
leaves the minerals behind the salinity of the oceans
is continually increasing. There is of course some
divergence of opinions as to how rapidly the salts
were carried down to the oceans in the earliest
ages, but no computation makes the time since the
oceans first started to form less than sixty millions
of years and some estimates run as high as one
hundred and forty millions of years.

The most recent geological method of determin-
ing the earth's age followed upon the discovery of
radio-active substances. Uranium degenerates by
the gradual breaking up of its atoms and radium,
lead and helium are evolved.

The relative amounts of these elements in some
33

SPLENDORS OF THE SKY

rocks show how long the process has been going on
in them. This method appears to give a greater
age for the earth than that obtained by any other
method. Those who have made a special study of
this method have arrived at the conclusion that
some of these rocks may be two billion years old,
and that their age at least must be measured by
hundreds of millions of years.

For the astronomer the vital question is, How
long has the sun kept up its present rate of radia-
tion ? Manifestly all life processes upon our earth
are dependent upon the light and heat furnished
by our sun. As soon as the supply begins to appre-
ciably and continually diminish life will begin a
rapid decline. The ruler of our solar system is
radiating heat and light into space at an extrava-
gant rate. The apparent area of the earth as seen
from the sun is about one-fifteenth the greatest
apparent area of Venus as seen from the earth.
From the sun the earth would appear as a small
point upon the celestial sphere. And yet how
much heat does our small planet intercept at a
distance of ninety-three million miles from the
sun? It has been estimated that the rate at which
solar energy is intercepted by the whole earth

34

SPLENDORS OF THE SKY

is 230,000,000,000,000 horse-power. The total
amount of the sun's radiant energy must therefore
be inconceivably great, for less than one two-
billionth of the total amount given forth is inter-
cepted by the earth. Except for the amount inter-
cepted by the other planets, placed at ten times
the amount the earth receives, the boundless supply
of radiant energy given forth by our sun is wasted,
according to the ideas of man. It travels onward
through interstellar space at the rate of 186,000
miles per second to the stars beyond.

The theories that the sun's heat is kept up by
the combustion of the materials of which it is com-
posed, or that it is simply cooling off without any
replenishment of its loss of heat, lead to absurd
results and receive no consideration from astrono-
mers. In neither case, under the most favorable
suppositions, could its present rate of radiation be
kept up for more than two or three thousand years.

A theory that is more plausible than either of
the preceding considers that the sun's heat is main-
tained by the impact of meteoric matter. Astrono-
mers have estimated that if a meteor should fall
into the sun from the distance of the earth its
velocity would be about 380 miles a second and the

35

SPLENDORS OF THE SKY

heat produced by the impact would be about 23,000
times the amount produced by the combustion of
an equal amount of carbon and oxygen. The
strongest objection to this theory is that it would
require a much larger total mass of meteors than
actually exists. Not a sufficient amount of meteor-
ic matter could possibly exist within the earth's
orbit for this purpose, and if it came from beyond
the earth's orbit the earth would also receive suf-
ficient amounts to materially affect its tempera-
ture. As a matter of fact the amount of heat that
the earth actually does receive from meteoric
matter is negligible.

The theory that the sun's heat is kept up by its
own contraction is the only one that at all fits in
with the requirements, and there are serious ob-
jections to regarding contraction as the only source
of supply of the sun's heat. Nevertheless, it can
be shown, following the methods of Helmholtz and
using the most recent data for the sun's rate of
radiation, volume and mass that a contraction of
120 feet a year in the sun's radius would produce
as much heat as the sun now radiates annually.
This amount of contraction is so small that ten
thousand years would elapse before the resulting

36

SPLENDORS OF THE SKY

change in the apparent diameter of the sun could
be detected from the distance of the earth with the
assistance of our most powerful telescopes. So
whether the sun actually is contracting cannot be
determined observationally. A weak point of the
contraction theory is that the present rate of radia-
tion of the sun could not have been maintained by
contraction alone for more than twenty-five mill-
ion years at the most. This would imply that all
the great series of changes that geologists and
biologists have every reason to believe extended
over tens if not hundreds of millions of years were
crowded into a period of approximately twenty-
five million years. Most astronomers consider it
more reasonable to assume that the contraction of
the sun does not supply all of its heat, than to
assume that all the evidence of other scientists
collected from a variety of independent sources
is wrong.

With the discovery of radioactivity it was be-
lieved that the sun's supply of heat might be sus-
tained partly by disintegration of uranium and
radium, inasmuch as such disintegration is accom-
panied by the evolution of an enormous amount
of heat. Although it is not known definitely that

37

SPLENDORS OF THE SKY

these substances are found in the sun, helium, one
of the products of the disintegration of uranium
and radium, occurs in great abundance in the sun,
and, in fact, was first discovered there. Investi-
gations showed that if one part in eight hundred
thousand of the sun were radium, heat would be
produced from this source alone as fast as the sun
is radiating it at present>but that in two thousand
years hence half the radium would be gone and the
production of heat would be diminished one-half,
or that two thousand years ago the amount was
twice the present amount and the production of
heat was twice as fast. Since this is not in accord
with the factb we can conclude that the sun's heat
is not due to the disintegration of radium to any
great extent. Uranium yields results just as un-
satisfactory.

Of one fact we are certain, that an unbroken
chain of life has existed upon our planet for tens
of millions of years at least and in this period there
has been no great temperature change and no signs
of a steady progressive cooling of the sun. Glacial
epochs and warmer eras have alternated with each
other, but no sudden [or gradual change great
enough to destroy the chain of life has ever arisen,

38

CHAPTER VI

MYSTERIES OF MARS

THE ruddy planet Mars, always an object of
special interest to the inhabitants of our
planet, Earth, because of its nearness and the still
unexplained mystery of its surface markings, is best
studied when it is in opposition to the sun.

It is then on the meridian at midnight and visible
throughout the entire night, rising in the east at
sunset and setting in the west at sunrise.

At a near opposition, which occurs once in fifteen
or seventeen years, Mars is a most striking object
because of its fiery red color. These near opposi-
tions always occur in August, and the next one
will take place in 1924, when Mars will be only
34,000,000 miles from the earth. Mars will also be
in opposition to the sun in April, 1920, and in
June, 1922, since oppositions of Mars are separated

39

SPLENDORS OF THE SKY

by intervals of two years and two months. The
next three oppositions will be particularly favor-
able for observations of the surface markings of
this planet.

Owing to the rarity of the atmosphere of Mars
it is possible to observe actual surface markings on
this planet. Mars has no vast oceans such as exist
upon our own planet. Extensive desert tracts pre-
dominate and give the planet its characteristic
reddish color. The comparatively few dark spots
that are visible lie in the Southern Hemisphere
and are generally believed to be due to vegetation.
The atmosphere of the planet is so rare that the
climate is one of extremes, with a great daily range
of temperature. The seasons resemble those found
upon the earth, for the two planets have nearly the
same inclination to the ecliptic, but the Martian
year is nearly two of our years in length and the
Martian seasons last twice as long as our own. The
planet turns on its axis in a little more than twenty-
four hours, so the Martian day and night nearly
equal the terrestrial day and night in length.

In addition to the extensive, reddish, desert
patches and the dark patches due to vegetation the
north and south polar snow caps are distinctive

40

SPLENDORS OF THE SKY

features of the Martian surface, and their appear-
ance and disappearance with the seasons is well
known. It is only when we come to a consideration
of the Martian ' ' canals ' ' that we meet with a diver-
gence of opinions among astronomers. Though
there are still astronomers who have never seen the
canals and astronomers who deny their existence,
there seems to be fully as many who have observed
them and are firmly convinced of their actuality.

The theory of the late Prof. Lowell concerning
the much disputed canals was that they were chan-
nels of water bordered by strips of vegetation and
were built by intelligent beings for the purpose
of directing the water from the melting polar caps
through the desert tracts to the opposite hem-
isphere. According to this theory we see not the
water channels but the strips of vegetation grow-
ing upon the banks. More recently Prof. W. H.
Pickering has advanced a theory concerning the
nature of the larger and more important canals
which he speaks of as the "The Theory of Aerial
Deposition. "

According to this theory the major canals are
marshes or natural reservoirs fed by storm ladened
air currents that are constantly passing from re-

41

SPLENDORS OF THE SKY

gions of high pressure surrounding the melting
polar cap to the equatorial regions of low pressure.
The rotation of the planet upon its axis from west
to east and the resistance of the atmosphere en-
countered by these air currents in their passage
toward the equator would give them a curving
tendency. Therefore the marshes or canals fed by
these air currents through precipitation of their
moisture during the chill Martian nights would also
show the same curvature. By measuring the radius
of curvature for the more important north polar
canals Prof. Pickering arrived at a determination
of the velocity with which the moisture ladened
air currents blow and he found that the highest ve-
locity of the wind over any of the southward lead-
ing canals was about 230 miles per hour. This was
the velocity found for the northern portions of one
of the longest canals shortly after the storm had
started from the polar regions.

At the southern end of its course the velocity was
reduced to about nineteen miles per hour.

Prof. Pickering concluded from an extensive
study of the curvatures of various canals that it is
reasonable to assume that the wind in the northern
hemisphere of Mars does at time reach a velocity of

42

SPLENDORS OF THE SKY

230 miles per hour and that the maximum theo-
retical velocity cannot be much less than 324 miles
per hour nor the corresponding pressure of the
atmosphere less than one-quarter of the pressure
of the terrestrial atmosphere. This conclusion is
borne out, he believes, by other considerations such
as the small force of gravity on Mars, the trans-
parency of its atmosphere and the lack of perma-
nent oceans. Upon this assumption the boiling
point of water upon Mars comes out as 150 degrees
F. approximately.

As the north polar cap melts and diminishes in
size, the amount of moisture carried southward
by the air currents should also diminish, and there-
fore the atmospheric pressure and consequently the
velocity of the wind. As a result the curvature of
the canals should change slightly and they should
shift with the season. The greater the velocity of
the wind the less it will be deflected in its south-
ward journey. A slight shifting of the polar canals
has been noted at previous opposition of Mars, and
it is particularly desired to investigate this ques-
tion of the shifting of the canals at favorable oppo-
sitions.

According to the theory of Prof. Pickering the
43

SPLENDORS OF THE SKY

major Martian canals, those leading from the north
polar cap southward to the torrid zone, are not
necessarily the work of intelligent beings, but they
do serve the purpose of furnishing the northern
hemisphere with a supply of water in the form of
natural marshes or reservoirs during the long
northern summer until the south polar cap starts to
melt at the coming of the autumnal equinox. Since
Mars has no great oceans these marshy tracts are
most essential for the maintenance of vegetable and
possibly animal life upon the planet.

In addition to these larger and more important
canals there are many faint, narrow canals of a
secondary type. About 500 canals of the faint type
have been located and named at the Lowell Ob-
servatory. They are characterized by great uni-
formity and straightness and by the fact that
they appear late in the season and in great num-
bers.

Prof. Pickering, who is one of the leading ob-
servers of Mars, considers that the question of their
origin is still unsettled. It is unknown whether
they are artificial or an illusion, or mark the path
of occasional local storms. As to the visibility of
the canals of Mars, this depends, according to Prof.

44

SPLENDORS OF THE SKY

Pickering, largely upon the conditions of our own
atmosphere. Under excellent " seeing " conditions,
it is possible, he believes, to see all of the more
prominent canals with a four-inch telescope.

45

CHAPTER VII

THE ASTEROIDS

IN the vast expanse of space that separates the
orbit of the outermost member of the terrestrial
group of planets, Mars, from the nearest and larg-
est of the major planets, Jupiter, is found that
numerous host of tiny bodies known as the planet-
oids or asteroids.

Lawful members of the solar system they must
be considered, although they are distinguished from
the eight large planets not only by their extreme
minuteness, which renders the largest of them in-
visible without telescopic aid, but also by a greater
range in the shape of their orbits and in the in-
clination of these orbits to the earth's path around
the sun. The paths of the eight principal planets
can hardly be distinguished from perfect circles
and they lie very nearly in the same plane. The

46

SPLENDORS OF THE SKY

asteroids move in paths, that vary from almost per-
fect circles to highly elongated ellipses and these
paths are sometimes inclined at an angle of nearly
35 degrees to the planetary orbits, though the
average is much less. It is truly remarkable, how-
ever, that all of the asteroids so far discovered,
more than eight hundred in number, move in the
same direction around the sun as do the eight chief
members of the solar system, from west to east.
This cannot be the result of chance but points to a
common origin with the other members of the
system. According to the planetesimal theory of
the origin of our solar system the asteroids may be
regarded as particles of the original nebula that es-
caped fusion into one greater planetary mass, due
either to an absence of a planetary nucleus in their
immediate neighborhood or to the nearness of the
huge Jovian mass under whose disruptive influences
they have been kept apart. So interwoven are the
paths of the planetoids that if they were made of
wire not one could be lifted without drawing the
others with it. That they have so far escaped col-
lisions is due to the fact that their paths lie in
planes inclined at different angles. The noted little
asteroid Eros has escaped collision with the planet

47

SPLENDORS OF THE SKY

Mars only because of the inclination of its orbit.
At the time of the discovery of the first asteroid,
January 1, 1801, the first day of the nineteenth
century, astronomers were making preparations to
search for a planet in the enormous gap existing
between the orbits of Mars and Jupiter. Accord-
ing to Bode's law, to which is also due, indirectly,
the discovery of the planet Neptune, a planet was
to be looked for at about 2.8 times the earth's dis-
tance from the sun. This peculiar law, which has
no scientific foundation, gives a rough approxima-
tion to the relative distances of the first seven
planets from the sun, as well as the average posi-
tion of the asteroids. According to this relation-
ship noted by Bode, if the number 4 is added to
each number in the series 0, 3, 6, 12, 24, 48, 96, the
resulting series, 4, 7, 10, 16, 28, 52, 100, repre-
resents roughly the relative distances of the planets
Mercury, Venus, Earth, Mars, Jupiter and Saturn
from the sun, with no planet to correspond
to the number 28. It was this gap in the distances
that led the astronomers of that day to suspect the
existence of another planet at 2.8 times the earth's
distance from the sun. The first asteroid discov-
ered was at approximately 2.8 times the earth's

48

SPLENDORS OF THE SKY

distance from the sun. It was found later that the
planet Uranus, undiscovered at the time Bode's
law was first advanced, continued the series, since
its distance from the sun corresponds to the num-
ber 196. The law fails, however, for Neptune. The
planetoids are scattered throughout the entire
space between the orbits of Mars and Jupiter. A
few of them even come within the orbit of Mars
and a few others are found beyond the orbit of
Jupiter, but they occur in greatest numbers at the
distance corresponding to the number 28 in Bode's
series, or 2.8 times the distance from the earth to
the sun.

The first asteroid was discovered by Piazzi at
Palermo and was, by his wish, named Ceres, for the
tutelary goddess of Sicily. A year later the astro-
nomical world was surprised by the discovery of a
second small planet at almost the same distance as
the first. This was named Pallas. In 1804 a third,
Juno, was discovered; in 1807 a fourth, Vesta.
These four are the largest of the asteroids and their
diameters are respectively 485, 304, 118 and 243
miles, as determined by Barnard with the 36-inch
telescope of the Lick Observatory. Most of the
asteroids are much smaller. Many do not exceed

49

SPLENDORS OF THE SKY

five or ten miles in diameter. After the discovery
of Vesta in 1807 no other asteroid was discovered
until 1845, when Hencke's long search of fifteen
years was rewarded by the discovery of Astrsea. In
1847 three more were discovered and from that
time to the present, no year has passed without the
discovery of at least one asteroid. Since 1891,
when photography was first used for the purpose,
planetoids have been discovered in great numbers.
The telescope with photographic plate exposed in
place of an observer is made to follow the stars
for several hours. In this time the planetoid will
move an appreciable distance. When the plate is
developed the star images appear as clearly defined
dots, but the asteroid has left a telltale trail upon
the plate about a twentieth of an inch in length.
Following the discovery a provisional designation
is given to the object until it can be determined
definitely whether it is a new asteroid or simply
one rediscovered, or possibly a new comet. Wolf's
comet, discovered photographically in this way, was
at first mistaken for an asteroid. New plates must
be exposed or old plates reexamined to get addi-
tional positions of the object from which its orbit
is computed. Peculiarities of motion soon show

50

SPLENDORS OF THE SKY

whether it is asteroid or comet or possibly a faint
satellite of Jupiter or Saturn.

In 1898, when astronomers were growing weary
of their large and ever increasing family of aster-
oids, already numbered by hundreds, and when it
was becoming a perplexing question as to how they
were to be named and how time could be spared
from more urgent work to compute their trouble-
some orbits, asteroid No. 433, known as Eros, was
discovered. This tiny asteroid, less than twenty
miles in diameter, has more than repaid all the
work and trouble occasioned by the other members
of the family and has furnished astronomers with
probably the best method they possess for deter-
mining the solar parallax and the dimensions of
the solar system in miles and the distances of the
stars and the dimensions of our whole stellar sys-
tem as well. It is possible to determine the rela-
tive distances of the members of the solar system
without knowing the actual distance between any
two of them, but we can form no idea of the extent
of the solar system in miles and of the universe in
light years until we actually measure the distance
between two of the bodies. Eros comes nearer to
the earth than any other known celestial body with

51

SPLENDORS OF THE SKY

the exception of the moon. At nearest approach
it is only 13,500,000 miles away, and its nearness
and clear, staiiike image make it an ideal object
for the determination of the important constant of
the solar parallax and the distance from the earth
to the sun, the astronomical unit of distance. Eros
was in a particularly favorable position for obser-
vation in the winter of 1900-1901, and a series of
valuable observations were obtained. Thirty years
must pass before it will be as favorably located.
Eros aroused still further interest in 1901 when
it was observed to vary rapidly in light. During
February and March of that year its period of
light variations was 2 hours 38 minutes. Its light
at minimum was less than one-third that of maxi-
mum. By May of the same year this peculiar
variability had ceased. It was suggested that it
might be explained by assuming that the planetoid
consisted of two bodies revolving close together so
that one body would appear to eclipse the other in
certain positions of the orbit. According to an-
other view the asteroid has a surface that is very
rugged and uneven and reflects light unequally.
In other words, like most of the asteroids, it may
be considered to be simply a huge rock.

52

CHAPTER VIII

THE PLANETS JUPITER AND SATURN COMPARED

WHEN the two largest planets in the sun's
family, Jupiter and Saturn, appear in the
heavens at the same time, as frequently happens,
they can be readily distinguished from each other
since Jupiter far surpasses Saturn in brightness,
not only because it is much larger, but also because
it is much nearer to the earth. On the date of its
opposition to the sun, the giant planet Jupiter is
approximately 400,000,000 miles away, while Sat-
urn is nearly twice as far from the earth.

The two planets closely rival each other in pop-
ular interest. Saturn's vast system of three con-
centric rings, more than 170,000 miles in outer
diameter, composed of swarms of minute moonlets
of meteoric dimensions revolving each independ-
ently around the planet, makes it absolutely unique

53

SPLENDORS OF THE SKY

in the solar system. Jupiter, on the other hand,
on account of his satellites and belts, is by far
the most interesting to observe of all the planets,
as well as the largest and most imposing, and the
one most subject to constant change and variety of
color and markings. Though Saturn is also, beyond
doubt, the scene of wildest tumult, its surface
changes are rendered more blurred and indistinct
by an additional 400,000,000 miles of intervening
space.

There is much similarity in the surface markings
of the two planets, which are, in reality, phenom-
ena of the dense enveloping gaseous strata of their
atmospheres. Belts or bands of gaseous vapors are
always to be seen in the atmospheres of both plan-
ets, though the belts of Saturn are far more indis-
tinct than those of Jupiter. They vary contin-
ually in shade, numbers and position, but always
lie in a direction parallel to the planet's Equator,
being drawn into this position by the extremely
rapid peripheral motion of the outer gaseous en-
velopes of these planets.

Both Jupiter and Saturn rotate on their axes in
approximately ten hours, less than half the period
that the earth requires to turn on its axis, though

54

SPLENDORS OF THE SKY

its diameter is only about one-tenth that of the
outer planets.

It is an interesting and significant fact that the
general color of the planet Jupiter fluctuates with
the sun spot period, appearing palest when spots
are most plentiful on the sun and more reddish as
the frequency of sun spots decreases. This is due
to the fact that the solar activity that produces
sun spots also produces certain atmospheric effects
upon the planets. It is known that high clouds,
such as the cirrus clouds in the earth's atmosphere,
form more readily under the solar influences that
produce sun spots and similarly it is believed
atmospheric changes are produced in the dense
gaseous envelope of the giant planet.

Marked changes are also noted at times in the
color of the ringed planet. According to observa-
tions made at the Lowell Observatory at the op-
position of 1916 the planet was at that time of a
pinkish brown color and conspicuously darker than
its rings.

The great distance of Saturn makes it very
difficult to observe the finer details of its surface
changes. It is for the same reason that Saturn's
interesting satellite family of nine members,

55

SPLENDORS OF THE SKY

exactly equal in number to that of Jupiter and
fully as impressive in the actual size of its various
members, arouses less interest than the family of
the giant planet.

Titan, the largest of Saturn's satellites, a world
in itself, fully three thousand miles in diameter,
can be seen readily enough with the smallest tele-
scopes as an eighth magnitude star. Rhea, Dione
and Tethys, whose diameters are between twelve
hundred and fifteen hundrd miles, may also be
seen fairly well with a four-inch telescope, which
will also show the rings beautifully.

Japetus, the most distant of the satellites of
Saturn, with the exception of tiny Phoebe retro-
grading at a distance of eight million miles, is
almost the twin of our own moon in size. It lies
at a distance of two and a quarter million miles
from Saturn and requires seventy-nine days to
make one revolution around the planet. It is of
special interest to astronomers, owing to the fact
that its light is conspicuously variable. When on
the western side of Saturn it is always brighter
than when it is on the eastern side, and this is
believed to be due to the fact that it always keeps
the same face turned toward Saturn just as our

56

SPLENDORS OF THE SKY

own moon always keeps the same face turned
toward the earth. The variability of light prob-
ably arises from a difference in the reflecting power
of the two sides, different sides of the satellite's
surface being turned toward the earth in the two
positions.

Observations made of the first two satellites,
Mimas and Enceladus, by E. C. Slipher of the
Lowell Observatory seem to show that these satel-
lites also keep the same side turned toward the
planet. They are both small bodies between 500
and 1,000 miles in diameter that skirt rapidly
around the outer edge of the ring system distant
from its outer edge 30,000 and 70,000 miles re-
spectively.

The possessor of a small telescope will find the
four largest satellites of Jupiter easier and more
interesting objects to observe than Saturn's satel-
lites. A few extremely sharp-eyed persons have
glimpsed these four satellites with the naked
eye, and the least optical aid will reveal them.
Their journey ings around the giant planet and
all the varied phenomena of the eclipses, occul-
tations, shadows and transits can be observed with
interest and profit by means of a three-inch tele-

57

SPLENDORS OF THE SKY

scope. The five fainter satellites are beyond the
reach of all but the most powerful telescopes, as
are also the four smallest satellites of Saturn.

Jupiter and Saturn resemble each other not only
in the size of their satellite families and the nature
of their surface markings but also in the fact that
they are both composed almost, if not entirely, of
matter in a gaseous state. The extremely low
density of the two planets, less than that of the
sun in both cases, and in the case of Saturn only
sixty-three-hundredths that of water, the lowest for
any planet in the solar system, contrasts sharply
with the great density of the terrestrial planets.
Our own planet Earth, with its surface crust and
rigid interior, possesses a density five and one-half
times that of water.

The two planets, Jupiter and Saturn, are there-
fore as different in physical constitution from our
own world as it is possible for one to imagine.
They possess no stable surface crust, though liquid
and solid particles of matter may occur locally or
be suspended in dense gaseous vapors. All is a
whirling, seething, tumultuous mass, characterized
no doubt by great heat, in the deeper strata at
least, where the pressure of overlying gases must

58

SPLENDORS OF THE SKY

be tremendous. A small solid or liquid core may
exist in each planet, but the general belief is that
both planets are almost entirely gaseous. Though
the two planets may emit a certain amount of heat
to their satellites, the complete disappearance of
the satellites of Jupiter when they pass into his
shadow shows that they receive no appreciable
light from the huge planet other than reflected
sunlight.

A marked difference between these two planets
that have so many characteristics in common is
found in the positions of their axes of rotation with
respect to their paths around the sun. The equator
of Jupiter is inclined only three degrees to its orbit.
As a result it has no change of seasons. Saturn's
equator, on the other hand, as well as its ring
system, which lies nearly in the same plane, is tip-
ped twenty-seven degres to the plane of its orbit.
This inclination of equator to orbit is the greatest
for any planet in the solar system, exceeding that
of the Earth by several degrees. As a result season-
al changes on Saturn would be more pronounced
than they are on the Earth were the effect not modi-
fied to a great extent by the very great distance of
Saturn from the sun.

59

SPLENDORS OF THE SKY

In these two largest members of the sun's family
we see much that is similar and much that is dis-
tinctive. No two planets of the solar system are
modeled exactly along the same lines. This indi-
viduality among the various members of the same
planet family is but a reflection of the infinite
variety that characterizes all the wonderful form-
ations far beyond that form a part of the same uni-
verse to which our sun and his family belongs.

60

CHAPTER IX

SATURN THE RINGED PLANET

OF all the brighter planets Saturn is the least
interesting to observe with the naked eye and
one of the most interesting viewed through the tele-
scope.

It shines with a dull leaden light, very different
from the fiery red of Mars, the sparkling beauty
of Venus, or the splendor of Jupiter.

Saturn is usually spoken of as the ringed planet
and is unique in the solar system for several rea-
sons. It is the only planet that is lighter than
water, the only one that would float if thrown
into a body of water large enough to contain it,
and it is surrounded by a system of rings of mar-
velous appearance.

There are three of these thin, flat, concentric
rings, two bright ones and a third called the dusky

61

SPLENDORS OF THE SKY

or crepe ring. The outer ring, which is called
"A," has an exterior diameter of 173,000 miles
and a width of 11,000 miles. It is separated from
"B," which is much brighter, by a division of
2,200 miles of uniform width all around known as
Cassini 's Division. The third or dusky ring, ' ' C, "
was discovered in this country in 1850 and is com-
paratively hard to see. Its width is equal to that
of the outer ring and its inner edge is only 6,000
miles from the surface of the planet. The ring* * B "
is about 18,000 miles wide. The thickness of the
ring system is less than 100 miles and its weight
is next to nothing. "Immaterial light " the rings
have been called by the astronomer Struve. They
are of perfect symmetry and when seen in a
telescope fill the observer with admiration and
awe.

As to composition, they are now known to be
swarms of tiny satellites or moons, nothing more
than meteors in size, and they are in constant
revolution around Saturn. Every 15 or 17 years
the rings entirely disappear from view for a
short time even in the most powerful telescopes.
This is due to the fact that once every 15 or 17
years the earth is exactly in the plane of the rings

62

SPLENDORS OF THE SKY

and the edge of the rings is directly in the line of
sight. This causes the entire disappearance of
the rings from our point of view. The next dis-
appearance wiil occur in 1922.

For the remaining time the earth is either above
or below the plane of the rings and we either
look down upon them from above or up from be-
neath, as the case may be, and so see them at vary-
ing widths.

In addition to the rings Saturn has nine satel-
lites, and the outermost is at a distance of about
8,000,000 miles from Saturn. So extensive is this
vast system, truly a solar system in miniature ! The
names of the satellites in order of distance outward
from Saturn are Mimas, Enceladus, Tethys, Dione,
Rhea, Titan, Hyperion, Japetus and Phoebe. By
far the largest of these is Titan, which is of the
same size as the planet Mercury.

The most remarkable of the satellites is Phoebe,
because, while all the other satellites of Saturn
follow the usual direction of revolution in the solar
system and revolve from west to east around their
primary, Phoebe revolves from east to west or
retrogrades, as it is called.

The periods of revolution of the satellites around
63

SPLENDORS OF THE SKY

their primary show great diversity, ranging from
22y2 hours for Mimas, which skirts along the outer
ring, to 16 months for Phoebe, the most distant
of all. In shape Saturn is the most flattened at
the poles of any of the planets. It is decidedly
oval in appearance. This is very noticeable at the
time of disappearance of the rings, when we get an
unobstructed view of Saturn's globe. Saturn also
has belts, similar to those of Jupiter, but fainter in
color and more indistinct.

Both of these planets are apparently in a much
earlier stage of development than the earth. Saturn
is a world in a state of chaos, and the dense can-
opy of clouds, with which it is surrounded, points to
a surface of intense heat, for Saturn is too far from
the sun to have its clouds raised by solar heat.
They must be the product of its own seething heat.
This is a world in the making and the dense
clouds with which it is surrounded will probably
settle down upon its surface as oceans in ages
to come.

It is hard for us to realize as we look upon this
planet of leaden hue, not so much brighter than a
first magnitude star, so great is its distance from
us, that in size our earth compares with it as a

64

SPLENDORS OF THE SKY

pea with an orange, and that, as the celebrated
French astronomer Flammarion has said, the earth
might roll upon the ring system like a ball upon
a road.

CHAPTER X

PLAIN FACTS ABOUT THE MOON

A LL the planets in the solar system, with the
•**• exception of Mercury and Venus, are at-
tended by satellites. Saturn has nine, in addition
to his ring system, composed of numberless tiny
moonlets.

Jupiter also has nine moons, Uranus four, Mars
two and Neptune one, while our own planet, Earth,
has a satellite which is in one respect unique in the
solar system. The ratio of its size to that of its
primary far exceeds that of any other satellite.
Its dimensions are quite comparable with those of
the earth. Its diameter is about 2,160 miles. The
earth's diameter is about 7,900 miles.

Fifty moons would equal the earth in volume,
although it would take eighty-one times the mass
of the moon to equal the mass of our planet, as

ftt

SPLENDORS OF THE SKY

the lunar density is only six-tenths that of the
earth. The entire surface of the moon about equals
North and South America in area, though about
forty per cent, of its surface we can never see, since
our satellite always turns the same face toward us.

Titan, the largest satellite of Saturn, has a
diameter of 3,500 miles, and is larger than the
planet Mercury, but it would take 4,600 Titans to
equal Saturn in mass. Ganymede, the largest
satellite of Jupiter, is almost exactly of the same
size as Titan, but its mass must be increased 11,000
times to equal that of Jupiter.

Neptune's moon about equals our own in size, but
is a very tiny object compared with its primary,
which has a diameter of 35,000 miles. The largest
of the satellites of Uranus is only 1,000 miles in
diameter and the two tiny moons of Mars average
about ten miles in diameter.

Our own satellite is a most beautiful and inter-
esting telescopic object and even when viewed with
an opera glass, its apparent distance is reduced
one-half. With moderate sized instruments we
may view it at an apparent distance of about 1,000
miles. The greatest telescopes make it appear only
sixty miles away, but we must remember such a

67

SPLENDORS OF THE SKY

view is by no means clear and distinct, for atmos-
pheric imperfections are magnified as well.

Even with, moderate sized instruments, how-
ever, any lunar object a mile or so in diameter
is readily discernible, and with large instruments
and a trained eye and good atmospheric condi-
tions, any object a quarter of a mile in diameter
could be detected. If large cities existed upon the
moon very moderate instruments would show them.

The question of life upon the moon is readily
disposed of, for we know that there is neither air
nor water there. The moon's period of rotation
upon its axis is equal to its period of revolution
around the earth. In other words, it always turns
the same face toward the earth and its day is two
weeks long. Fourteen days of light are followed
by fourteen days of darkness.

During the lunar day the barren surface of the
moon is exposed to the intensity of the solar rays,
unmitigated by any protecting atmosphere. The
temperature must rise during this scorching period
as high as the boiling point, to fall during the long,
dark night that follows nearly to the absolute zero
of interplanetary space.

Because of the absence of an atmosphere upon
68

SPLENDORS OF THE SKY

the moon there is no diffusion of light. Shadows
are inky black and the stars above shine by day
and by night, in an inky sky. Stars that we need
a field glass to see upon the earth would be readily
seen with the naked eye upon the moon. The
Milky Way, so dimly seen by us, is a gorgeous
spectacle in the lunar heavens. The solar corona
and prominences are always visible, as is also the
zodiacal light. The planet Mercury, so elusive to
our eyes, is easily observed from the moon. Both
stars and planets shine far more brilliantly there
against a background that is always black.

As regards the lunar landscape, even the small-
est telescope shows us many features not visible to
the naked eye. Extensive dark and light regions
give our satellite its spotted appearance. The light
portions are always rough and the dark ones com-
paratively smooth. The latter have been incor-
rectly termed maria or seas ever since the time of
Galileo, who believed these grayish patches were
really vast expanses of water. They are designated
by such fanciful names as Sea of Clouds. Sea of
Serenity, Lake of Dreams, etc.

The most distinctive lunar features are the
craters, numbered by the thousands, and possibly in-

69

SPLENDORS OF THE SKY

correctly named, for we naturally think of a crater
as formed by volcanic action and it is by no
means certain that the craters of the moon are
of volcanic origin, though this belief is still held
by some astronomers.

The larger craters, which are often from fifty
to one hundred miles in diameter, are usually com-
paratively shallow, about three miles or less in
depth. Frequently a single mountain a mile or so
in height rises from the centre of the crater, or
ringed plain, as it is often called. It has been
estimated that there must be fully 100,000 craters,
ringed plains and craterlets upon the surface of
our satellite. It is these formations that make its
face appear so pockmarked and scarred.

A conspicuous crater, visible even to the naked
eye, is Tycho, often called "the metropolitan crater
of the moon." It lies near the south pole of the
moon, has a diameter of over fifty miles and is
nearly 17,000 feet deep. It has a central hill 6.000
feet high and is a typical lunar crater.

The moon is also remarkable for its systems of
rays or streaks radiating from prominent craters.
These extend for vast distances, nearly 2,000 miles
in one instance. Those surrounding Tycho emanate

70

THE MOON — AGE, %% DAYS

(Photographed by Ritchey at the Yerkes Observatory)

SPLENDORS OF THE SKY

from it like brilliant lines of longitude. They
appear to be neither elevated nor depressed, but
run in remarkably straight lines over hill and plain
interrupted by no feature of the lunar landscape.

These rays still remain one of the riddles of the
moon, though, according to those who believe in
the meteoric origin of the moon they were caused
by the splashing of some light colored material
when an unusually large meteor struck the lunar
surface. Supporters of this belief point also to
the fact that large deposits of sulphur upon the
moon's surface have been photographed in ultra-
violet light.

A number of craters are surrounded by these
streaks. Copernicus, a crater a little northeast of
the centre of the moon's disk, has a remarkable
system of feathery streaks.

Clefts, or rills, as they are called, are also seen
in large numbers upon the moon. They are often
more than 100 miles long, but are usually extremely
narrow, often mere cracks in the surface, half a
mile or so wide. Mountain chains also exist upon
the moon similar to mountain chains upon the
earth. There are the lunar Alps and Appenines,
with peaks running up to 20,000 feet in height.

71

SPLENDORS OF THE SKY

On the extreme southern edge of the disk are two
mountain chains spoken of by the French astrono-
mer Flammarion as the "mountains of eternal
light/' for the sun never sets upon these peaks,
one of which is 7,000 feet higher than Mount
Everest.

From the moon the earth appears about thirteen
times as large as the moon does to us. Seen from
any point upon the visible lunar disk it would
appear practically immovable in the sky, its alti-
tude varying for different positions on the moon's
surface. The diurnal rotation of the earth would
be clearly seen, as would also its continents and
seas, polar caps, mountains and plains, its clouds
and storms. It would exhibit all the phases that
the moon does to us in reverse order.

Many theories of the origin of the moon have
been advanced, but all seem to present some diffi-
culties. Our satellite furnishes us many unsolved
problems. A belief in the meteoric origin of the
moon is now quite general. According to this be-
lief the earth was surrounded in the early stages
of its existence by a ring of meteoric matter. The
material forming the ring gradually gathered into
one mass, our present moon, whose pitted face gives

72

SPLENDORS OF THE SKY

evidence of the bombardment it received from
meteoric masses within the ring.

According to this theory our satellite has always
been a dead world, a cold and lifeless mass of
meteoric rock. It has never felt the pulse of life
or undergone the mighty changes that have passed
over its ruling planet, the Earth. It has remained
a cold and silent witness to vast evolutionary proc-
esses going on upon a neighboring world such as it
could never experience for itself.

73

CHAPTER XI

SOME UNSOLVED PROBLEMS OF THE MOON

A MOST troublesome little member of the sun's
•* *• family is our satellite, the moon. The nearest
to the earth of all the heavenly bodies and the most
easily observed, the moon presents as many un-
solved problems as the stars themselves.

There are more theories advanced to explain
the origin of the lunar craters than there are to
explain the nature of the "canals" of Mars. "We
hear many conflicting theories. First there is the
theory of a terrific explosion from within and the
resulting deluge of the lunar surface with an out-
flow of highly heated material of spongy consist-
ency with its bursting bubbles of gas, to be fol-
lowed later by secondary explosions and more
deluges. Then there is the opposite theory of in-
tense bombardments by meteoric masses from with-

74

SPLENDORS OF THE SKY

out that have disfigured and pitted the face of our
satellite.

There is also the theory that the moon was once
a part of the earth and that the two gradually
separated and the distance between them increased
slowly under the complicated action of tidal forces
exerted by the sun as well as by the earth and
moon. And there is another theory that the moon
never was a part of the earth but has been captured
by our planet.

There is one problem presented by irregularities
in the motion of the moon that transcends all other
lunar problems in importance. Indeed, it may
lead to discoveries bearing on the nature of gravi-
tation itself. It has long been known that the
motion of the moon is not in keeping with the
theory. The observed positions of the moon are not
in good agreement with the computed positions and
since the theory has been carried to a high degree
of accuracy it is now suspected that the difference
is due to the action of some unknown law that may
be as fundamental as the law of gravitation.

The positions of most of the members of the
solar system can be computed over an interval of
a number of years, according to the law of gravi-

75

SPLENDORS OF THE SKY

tation, with such a high degree of accuracy that the
observed and computed positions are practically
identical. The same cannot be said of the moon,
however. For half a century or a century the moon
will revolve around the earth a little ahead of its
regular rate and then for another long period of
time will gradually fall behind. Empirical cor-
rections are constantly being applied to the moon's
position in order to bring the observed and pre-
dicted positions into agreement.

So complicated is the theory of the moon that
only astronomers possessing the highest mathe-
matical ability are fitted to cope with it. Noted
mathematicians and astronomers have spent years
of effort in trying to discover the cause of the large
and continually increasing discrepancies between
the predicted and observed positions of the moon.

New tables for computing the position of the
moon have recently appeared. They are the result
of years of work by Prof. E. W. Brown of Yale
University, one of the best known theoretical
astronomers of the present day, and a number of
assistants. It is believed that these tables give the
moon's position with as high a degree of accuracy
as it is possible to obtain it by taking account of

76

SPLENDORS OF THE SKY

all known factors affecting the motion of our satel-
lite. Nevertheless, positions of the moon computed
with the new tables do not agree with the ob-
served positions, and it is evident that there is some
unknown factor in operation that is affecting the
motion of the moon.

Comparisons of the observed with the predicted
times of beginning and ending of totality in total
eclipses of the sun by the moon show the amount
of error in the computed position of the moon at
the time of the eclipse.

It was found in 1900 that the predicted time of
the beginning of the total eclipse was seven seconds
too early and the path of the moon's shadow upon
the earth was consequently a mile or two in error.
In 1905 astronomers were surprised to find the
difference had increased to twenty seconds, and in
the total eclipse of June 8, 1918, the predicted time
would have been in error eighteen seconds if a cor-
rection had not been applied shortly beforehand,
which reduced the amount of the error almost to
zero.

This correction was found from recent observa-
tions of occultations of stars by the moon. Since
the positions of the stars can be obtained with a

77

SPLENDORS OF THE SKY

high degree of accuracy the true position of the
moon can be found for the time when the star is
occulted or hidden behind the disk of the moon.
Observations of eclipses and occultations are used
to correct the tables that are used to predict the
moon's position from year to year, but these cor-
rections are empirical and it is not known yet to
what they are due.

It will be remembered that an unexplained
error in the computed positions of Uranus finally
led to the discovery of the planet Neptune, which
was producing the deviations in the predicted places
of this planet. The irregularities in the moon's mo-
tion cannot be attributed to an undiscovered planet,
however, and there is a strong possibility that there
may be something in the nature of gravitation itself
that is producing the discrepancies.

According to a theory that has been recently ad-
vanced by Prof. See of the Naval Observatory at
Mare Island, Cal., gravitation is to be considered
as an electro-magnetic force. He believes that the
unexplained deviations in the moon's position are
caused by the refraction, dispersion and absorption
of some of the magnetic forces of the sun by the
earth at the time of full moon and more especially

78

SPLENDORS OF THE SKY

at the time of the eclipse of the moon by the earth.
It appears that this explanation may account for
one of the unknown terms but it does not account
for all of them.

It may happen that when the cause of the errors
in the moon 's computed positions is found a funda-
mental law of the universe will be discovered as
well. It is in just this way that many valuable and
important discoveries are made. The velocity of
light was discovered while attempts were being
made to explain errors in the computed times of the
eclipses of Jupiter's satellites. Bradley made sev-
eral very important discoveries, such as the aberra-
tion of light and the nutation or wabbling of the
earth's axis that affects the positions of all the
stars, while he was attempting to measure the dis-
tances of the stars. So it will be by no means sur-
prising if our troublesome little moon some day
figures in a very far reaching discovery.

The moon's attraction for the earth gives rise
to the tides so familiar to every one. The sun also
produces tides upon the earth, but as the sun is so
much further away its tide raising forces are
inferior to those of the moon.

A small amount of light and heat is reflected
79

SPLENDORS OF THE SKY

from the moon to the earth and there are
minute variations in the position of the magnetic
needle to be attributed to the moon's influence,
as well as some minor changes in the earth's motion.
Aside from this the moon does not affect in the
least conditions existing upon the earth, though
there is no other heavenly body that is associated
with more superstitious beliefs.

To follow the course of the moon through the
heavens during one month, the period of its revo-
lution around the earth, and to explain the cause
of its various phases is a very elementary matter,
yet it appears to be a most perplexing problem for
nearly every one. In the present age, when astro-
nomical knowledge is so easily obtained, artists still
delight in placing the crescent moon overhead at
midnight, an astronomical blunder as serious as
picturing the sun in the west early in the morning.
Less frequently the horns of the crescent moon are
turned toward the horizon, though a moment's
thought would demonstrate the absurdity of this
position if the cause of the moon's phases is at all
understood. A most woeful lack of knowledge,
either of the cause of the phases of the moon or of
the relative distances of the stars and the moon,

80

SPLENDORS OF THE SKY

is evidenced when a star is pictured between the
horns of the crescent moon.

A knowledge of the elementary facts concerning
the moon and its motion is as easily acquired as is
the knowledge of the cause of the rising and setting
of the sun and the changing seasons, and it seema
quite unbelievable that there should be widespread
ignorance of such simple, yet fundamental, matters.

81

CHAPTER XII

SHOOTING STARS AND METEORS

UNTIL the beginning of the nineteenth century
it was deemed an absurdity to believe that
stones fell to earth from the heavens. Such rumors
had persisted for centuries, but they were attrib-
uted to the ignorant and superstitious.

Finally, in the year 1803 man was compelled to
change his views somewhat suddenly; not in some
far away corner of the earth, but over an extent of
many miles in thickly populated districts of France
thousands of such stones fell in a single day.
Their appearance was accompanied by the sharp
reports and detonations now known to be always
attendant upon the passage of meteorites through
the earth's atmosphere.

Scientists sent to the district by the French In-
stitute heard accounts of the phenomenon as seen

82

SPLENDORS OF THE SKY

by hundreds of eye witnesses and brought back
many of the stones.

After man's mind was open to conviction it was
found that the fall of meteoric stones from the
heavens was by no means a rare occurrence, though
their appearance in such large numbers as had
been observed in France in 1803 was unusual. It
has been concluded from a conservative estimate
that the number of large meteorites or aerolites that
reach the earth yearly must approximate fully one
hundred in number.

This estimate includes also those that fall in un-
inhabited lands or into the large bodies of water
that cover three-fourths of the earth's surface. In
addition to the meteorites that weight anywhere
from a few pounds to several tons, it has been esti-
mated from extensive observations that between
ten and twenty million meteors or shooting stars
enter the earth's atmosphere daily. Their average
weight is considerably less than an ounce and they
are usually consumed by the friction produced by
their rapid flight through the air. The resulting
dustlike particles float in the air or gradually settle
to the earth's surface, adding to its mass a few
tons daily.

83

SPLENDORS OF THE SKY

Though this seems to be a considerable amount,
it is so small in proportion to the earth's total mass
that it would not become appreciable for many
hundreds of thousands of years. These meteors
are believed to be the debris of comets encoun-
tered by the earth in its journey around the sun.
If the earth is continually encountering meteoric
dust, so, doubtless, are all the other planets as
well, and the total amount within the solar system
must be very considerable.

Astronomers are now giving a good deal of at-
tention to the question of the scattering of light
by cosmical dust throughout the universe at large
and there are indications of the presence in our
own solar system of appreciable quantities of finely
divided matter.

Interplanetary space is by no means a void.
Tails of comets appear at times to be brushed aside
or cut off in a manner quite unaccountable, unless
we assume that some resisting medium has been en-
countered such as would present no difficulty to
a larger mass, satellite or planet, but becomes very
disturbing to such tenuous matter as the tails of
comets.

The motion of Mercury is not just as it would be
84

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if affected only by the attraction of the known
planets. This has led to the suspicion that there
may be one or two small intra-mercurial planets,
and they have been searched for diligently at times
of total eclipse of the sun, so far unsuccessfully.
Some astronomers believe, however, that finely di-
vided particles of matter existing in the Zodiacal
Light may account for the peculiar behavior of the
innermost planet.

After sunset in the spring or before sunrise in
the fall, when the ecliptic rises most sharply from
the horizon, the careful watcher may see a faint
wedge of light, about equal in brightness to the
Milky Way, extending from the horizon to the
zenith. Near the horizon it is fully twenty degrees
wide, but it rapidly narrows to a width of three
degrees or four degrees overhead. Under favor-
able conditions it can be traced far beyond the
zenith. This is called the Zodiacal Light and ex-
actly opposite the sun also appears at times a faint
oval patch of light covering an area about the size
of the bowl of the Big Dipper. This is the Counter-
glow, and it is so excessively faint that few have
ever observed it.

Both Zodiacal Light and Counter-glow are un-
85

SPLENDORS OF THE SKY

observable if there is any moonlight. It is be-
lieved that the Zodiacal Light is due to reflected
sunlight from a great number of finely divided
particles circulating around the sun in the plane
of the earth's orbit and extending even beyond the
earth. The Counter-glow is not so easily explained,
but it probably represents a condensation of these
particles at some point beyond the earth's orbit at
a point about 930,000 miles from the earth and
just beyond the reach of its shadow where the com-
bined forces of the earth and sun would cause mat-
ters to be drawn into a sort of whirlpool of mo-
tion. Sunlight shining upon these particles makes
them visible to us when directly opposite the
sun.

So it appears that cosmical dust and fragment-
ary matter is fairly plentiful within our solar
system. Probably a large amount of such meteoric
dust is swept up by the larger planets as they jour-
ney around the sun, but the supply is also replen-
ished by the escape of particles of matter from the
atmospheres of sun and planets.

The sun is the seat of intense activity and ex-
plosive agents are at work there that cause flames
of the lighter gases to shoot forth at times to

86

SPLENDORS OF THE SKY

heights of more than 300,000 miles with velocities
of about two hundred miles or more per second. A
velocity of more than three hundred and eighty
miles per second would enable particles of matter to
permanently escape from the control of the sun and
pass to space beyond. Light pressure acting upon
small particles of matter may also overbalance the
sun's attraction and drive cosmical dust away from
the vicinity of the sun. The corona, we know, is
partly composed of dust particles and liquid glob-
ules shining by reflected sunlight as well as light
of incandescence.

Most interesting of all fragmentary matter ex-
isting within our solar system are the meteorites
previously mentioned. There are several theories
concerning the origin of these peculiar stones. The
idea that they are simply larger portions of dis-
rupted comets is quite generally held, and yet
these stones rarely appear when showers of meteors
are experienced. They almost invariably appear
singly.

The fact that they contain no unknown elements
and in some respects resemble lava from deep vol-
canoes led to the old belief that they were expelled
from the interior of the earth or other planets by

87

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intense volcanic activity in the past and after re-
ceding to great distances returned and fell once
more within reach of the earth's attraction. This
belief leaves unexplained many of the characteris-
tics of meteorites. Volcanic action intense enough
to overcome the effect of the earth's attraction
would cause a fusion of the material of which the
meteorites consist such as does not appear.

In some few instances meteorites are composed
of nearly pure iron, but usually they are frag-
ments of stone with peculiar crystals and consid-
erable quantities of gases that are sometimes com-
bustible, hidden in their crevices. They usually
show none of the results of the action of water and
very little oxidation. Some show veins where for-
eign substances have been slowly deposited and
signs of fracture and sliding of one surface on an-
other.

The most interesting theory respecting these vis-
itors from the heavens is that they are fragments
of disrupted bodies, possibly of planetary dimen-
sions, that at some time chanced too near a larger
mass and were torn asunder under tidal stress and
strain.

It is even a possibility that the solar nebula,
88

SPLENDORS OF THE SKY

from which we believe our present solar system
was fashioned, originated in the close approach of
two suns and that around one or both of these suns
at that time planets were circling. The tremendous
tidal reaction between the two suns would result
in streams of matter being ejected and the forma-
tion of a spiral nebula.

If planets encircled these suns they would be
completely shattered and scattered as meteoric
fragments. The larger nuclei of ejected matter
would gradually increase in size by sweeping up
other fragments of matter and become the chief
planets of another system. Smaller nuclei in the
vicinity of larger ones would form the satellites
attendant upon the planets. The eight hundred or
more asteroids may represent smaller independent
masses that have avoided collisions, while comets
and meteors are the debris remaining when order
has finally been brought out of chaos.

During the course of millions of years all frag-
ments of considerable size would be captured by
the major planets and satellites. In fact, the scan*
on the face of our satellite, many believe, are due
to terrific meteoric bombardment in the past. Ac-
cording to this latest theory of the possible origin

89

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of meteorites, fragments of worlds antedating our
own may fall to the earth's surface every year by
scores, and in a few cases find their way into our
museums.

90

CHAPTER XIII

OUR CELESTIAL VISITORS, COMETS

THE number of comets that are observed and
recorded is enormous, but most of these are
telescopic and conspicuous comets are few. Hardly
a year passes without the appearance of several of
these mysterious visitors. Some of these comets
are old friends returning, periodic comets that ar-
rive more or less on schedule time, while others
that travel in greatly elongated ellipses only ap-
proach the sun once in hundreds or even thousands
of years. Donati's great comet of 1858 takes 2,000
years to complete its circuit. It is a question
whether some comets ever return to the solar re-
gions again, for their orbits appear to be parabolic
rather than elliptical. Since, however, we can ob-
serve only a very small portion of the orbits of
some comets that penetrate far into the depths of

91

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space beyond the orbit of Neptune and since the
arc of both ellipse and parabola are nearly coin-
cident for the short interval of observation we are
left in doubt as to whether all comets return or not.

Some may speed forth into the immensity of
space that separates our solar system from the
stars beyond never to return, but there are com-
ets in great numbers that are known to be per-
manent members of the solar system, and that ac-
company it on its onward journey through space.
They encircle the sun in orbits that are greatly
elongated ellipses markedly different from the
nearly circular orbits of the planets.

If a comet on its journey around the sun passes
close to one of the major planets, it may come
under the gravitational influence of that planet to
such an extent that its path will be entirely
changed and its aphelion or the point of its orbit
furthest away from the sun will afterward lie close
to the orbit of that planet. Jupiter has a family
of about thirty comets. His family is the largest
because his mass is greater than that of all the other
planets combined. All the aphelia of these cap-
tured comets, of course, lie near Jupiter's orbit.
Neptune has a family of six comets.

92

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There are two or three groups of comets whose
aphelia lie at distances several times as great as
Neptune's distance from the sun, and possibly fu-
ture investigations of cometary orbits of long pe-
riod may lead to the discovery- of several trans-
Neptunian planets. There is no reason to suppose
that Neptune is the farthest planet from the sun,
for the gravitational influence of the sun extends
enormously beyond it.

Comets of short period are usually spoken of as
periodic comets. The shortest period, three and
one-third years, is that of Encke's comet, which,
when furthest from the sun, never gets beyond the
orbit of Jupiter, while Halley's noted comet, which
made its last return in 1910, has the longest period
of comets classed as periodic. No great or con-
spicuous comet belongs to this class.

Though comets are the bulkiest of all heavenly-
bodies, they are also possessed of the least mass of
any known bodies that travel through space. Com-
ets usually consist of a nucleus, coma or head, and
tail. The nucleus, which in great comets fre-
quently appears as bright as first magnitude stars,
is no more than a swarm of meteoric particles. Of
the actual size of the particles we can form no

93

SPLENDORS OF THE SKY

idea, but they are evidently held together by a
very loose bond of gravitation. The entire nucleus
is enwrapped in a gaseous envelope that forms the
head of the comet. This coma or head is often of
enormous dimensions. The head of Donati's comet
was 250,000 miles in diameter, while the head of
the comet of 1811 measured over 1,000,000 miles
at one time. As the comet approaches close to the
sun the head is observed to contract or diminish in
size.

The tail, which is the most noticeable and dis-
tinctive feature of a comet, does not develop until
it draws in toward the sun. It then becomes, in
many cases, millions of miles in length. The Great
Comet of 1843 had a tail more than 200,000,000
miles in length and the comet of 1882 had a head
200,000 miles in diameter and a tail 100,000,000
miles long. These two comets, as well as the great
comet of 1880, pursued nearly identical paths. All
three were noted for their close approach to the
sun. The comet of 1843, in fact, passed through
the corona and within 32,000 miles of the sun's
surface, and only its enormous velocity of several
hundred miles per second saved it from actually
falling into the sun. Its enormous tail appeared

94

BROOKS' COMET

(Photographed by Barnard at the Lick Observatory)

SPLENDORS OF THE SKY

to be whirled around the sun in about two hours
and this fact proved conclusively that the tail could
not be an actual appendage, but must be a series
of emanations from the head due either to the elec-
tric repulsion of the sun acting upon highly rare-
fied material in the head of the comet or to light
pressure which overbalances the effect of gravity
in the case of particles of extremely small mass.

Comets shine not only by reflected sunlight, but
by inherent light as well, and the spectroscope
shows that they are composed chiefly of gaseous
compounds of hydrogen and carbon, though when
near the sun metallic lines of sodium and iron fre-
quently appear. So highly rarefied is the material
composing the heads and tails of comets that faint
stars are often observed to shine through them
undimmed, even when close to the nucleus. The
fact that the earth has many times been involved
in the tails of comets with no disastrous conse-
quences— in fact, without our knowing it until
later — shows the flimsy nature of these appendages.
If the earth should meet a comet head on, how-
ever, it would doubtless experience a more or less
severe meteoric shower, depending upon the size
of the meteoric stones within the nucleus.

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SPLENDORS OF THE SKY

Continued returns of periodic comets to the vi-
cinity of the sun tend to reduce them greatly in
size and brilliancy and it is for this reason that
none of the short-period comets are as striking or
conspicuous objects as the great comets of long
periods and infrequent returns. Even Halley's
comet, the largest and most noted of periodic com-
ets, was a decided disappointment as a "show"
comet upon its return in 1910. Meteoric showers
are composed of the debris of comets that have be-
come disintegrated, and comets have been seen to
separate into two or more branches. Many comets
travel in groups along the same curve. The great
comets of 1843, 1880 and 1881 belong to such a
group. They follow practically the same path and
may have even formed one enormous comet at some
time in the past.

It is not so many years since the visits of these
mysterious strangers were received with dread and
fear, for it was believed that they predicted evil,
either war, famine, pestilence or death of royalty.
Needless to say, such fears were entirely without
foundation, but so superstitious are the masses that
even to the present day traces of these beliefs still
linger. In 1910 when Halley's comet made its

96

SPLENDORS OF THE SKY

predicted return, Chinese mobs attempted to
frighten away the unwelcome visitor with flaring
torches. If a great and conspicuous comet had
made a sudden appearance just prior to August,
1914, we might have found that " civilized " west-
ern nations, even in this age, are not so entirely
free from superstitious fear concerning unusual
heavenly phenomena as we might like to believe.

97

CHAPTER XIV

HOW CARBON DIOXIDE IN THE EARTH'S ATMOSPHERE
AFFECTS CLIMATE

\ CCORDING to the scientists, man's extra va-
-**• gant consumption of coal may, in the course
of a very few centuries, materially affect the com-
position of the atmosphere and thereby the average
yearly temperature at the earth's surface and cli-
matic conditions.

Carbon dioxide, which is the product of the com-
bustion of coal, is one of the constituents of the
atmosphere. The amount of this compound found
in the atmosphere is extremely small, three-hun-
dredths of one per cent, by volume, five-hundredths
of one per cent, by weight. Although the percent-
age of carbon dioxide is so small it has an appreci-
able effect upon the earth's climate.

The amount of coal mined and burned annually
98

SPLENDORS OF THE SKY

is approximately one billion tons, and as a result
of this combustion a little over three and a half
billion tons of carbon dioxide are added yearly to
the present amount of carbon dioxide in the earth's
atmosphere, which is approximately three trillion
tons.

A simple computation will show that the amount
of carbon dioxide in the atmosphere will be doubled
in about eight hundred years if the present rate
of combustion of coal is maintained.
. The absorbing properties of carbon dioxiae are
practically the same as those of water vapor. The
intensely hot rays of the sun of shortest wave
length, those from the blue end of the spectrum,
pass through the carbon dioxide and water vapor
in the air as readily as through nitrogen and oxy-
gen, the chief constituents of the atmosphere, but
the longer heat rays, as they are called, from the
red end of the spectrum suffer strong absorption
by the carbon dioxide and water vapor in the
earth's atmosphere.

The radiations from the earth's surface are com-
posed almost entirely of the rays of longer wave
lengths and are, therefore, largely absorbed by
these compounds. The blanketing effect of the at-

99

SPLENDORS OF THE SKY

mosphere is greatly increased by the presence of
water vapor and carbon dioxide. It has been esti-
mated that fully thirty-five per cent, of the sun's
rays that enter the atmosphere of the earth per-
pendicularly are absorbed before they reach the
surface of the earth.

At night the heat absorbed by the atmosphere
during the daytime is radiated in all directions and
portions of it strike the earth's surface directly
and warm it, while other portions are reflected
back to the earth from the upper atmosphere. Also
the heat rays radiated from the earth's surface
during the night are trapped by the water vapor
and carbon dioxide in the atmosphere and raise
the temperature of the air.

As a result the extremes of temperature be-
tween day and night are greatly reduced by the
presence of these two compounds in the atmos-
phere.

Every one is aware of the fact that on the moun-
tain heights where the atmosphere is less dense the
days are hotter and the nights colder than they
are at sea level. It is also well known that the
early autumn frosts occur only when the air is
clear and the amount of water vapor in the atmos-
100

SPLENDORS OF THE SKY

phere small. An increase in the amount of carbon
dioxide in the air would have the same effect on
the temperature as an increase in the amount of
water vapor, since the heat absorbing properties
of the two are the same.

Certain geologists believe that the amount of car-
bon dioxide in the earth's atmosphere has varied
periodically over long intervals of time and that
the glacial periods and the warm periods that have
occurred alternately in the past have been due to
this variation in the composition of the atmosphere.
The effect of an increase in the amount of carbon
dioxide in the earth's atmosphere is to increase the
general temperature of the air, while a decrease
in the amount of carbon dioxide lowers the sur-
face temperature of the earth.

The enormous amount of coal burned by the
human race yearly will, therefore, in the course of
time, increase the earth's temperature and affect
the climate throughout the world. Whatever af-
fects the nature or direction of the air currents
that flow over the earth's surface will possess the
greatest influence over the general temperature of
the world, for to the air currents and their equal-
izing effect upon the climate is to be attributed the
101

SPLENDORS OF THE SKY

habitability of both the polar and tropical regions
of the earth.

The composition of the atmosphere has the great-
est influence over the forms of life existing upon a
planet, and in considering the question of life on
other planets the nature and composition of the
atmosphere is first in importance.

It is extremely difficult to speculate concerning
the forms of life one would meet on Mars or Venus
until we know something definite about what ele-
ments and compounds occur in the atmosphere of
these planets and in what proportions. Even small
variations in the amount of carbon dioxide in the
earth's atmosphere can seriously affect its climate.
A slightly greater percentage of this compound in
the atmosphere of Mars might go far toward over-
coming the greater extremes of temperature be-
tween day and night arising from a rarer atmos-
phere and greater distance from the sun.

Then, too, the relative amounts of nitrogen and
oxygen in a planet's atmosphere would have to be
taken into consideration in speculating on the pos-
sibility of the existence of red-blooded organisms
that require a large percentage of oxygen for their
development

102

SPLENDORS OF THE SKY

The elements that enter into the composition of
the earth's atmosphere and the percentage of these
elements in a given volume are : Nitrogen, seventy-
eight per cent. ; oxygen, twenty-one per cent. ; ar-
gon, ninety-four hundredths of one per cent. There
are, in addition, extremely small amounts of kryp-
ton, helium, neon, xeon and other rare elements.
The amount of water vapor in the air is, of
course, variable and can never exceed a certain
amount, and the amount of carbon dioxide, as we
stated before, is only three-hundredths of one per
cent.

There are in addition to these elements and com-
pounds a number of impurities, such as ammonia,
Hoot and dust particles that occur in extremely
Kmall amounts as a rule. We might also include the
poisonous gases and compounds that man has em-
ployed during the present war, though their sum
total is infinitesimal and probably surpassed in
1otal volume by the gases arising from a single
volcanic eruption.

The height of the earth 's atmosphere can be de-
termined by observing the flight of shooting stars
or meteors and the altitude of the auroral stream-
ers from two different positions on the earth's sur-
103

SPLENDORS OF THE SKY

face, observations being made simultaneously at
the two stations, or it can be determined from the
duration of twilight. The results vary according
to the method used, since the density of the atmos-
phere decreases rapidly with increased distance
from the earth and the different phenomena occur
at different densities.

The atmosphere extends fifty miles above the
earth in quantities sufficient to produce twilight.
It has been found that it is sufficiently dense to
offer resistance to meteors at a height of 100 miles
from the earth. The southern ends of auroral
streamers are usually more than 100 miles in
height; and they sometimes reach a height of 500
miles.

The aurorae are electrical phenomena of the rare
upper atmosphere and the density required for
their display is very slight. It is usually consid-
ered that the atmosphere does not occur in ap-
preciable-amounts to more than 100 miles from the
earth's surface.

The weight of a column of air reaching from

the earth's surface to the limits of the atmosphere

and one square inch in cross section weighs fifteen

pounds, and from the known area of the surface of

104

SPLENDORS OF THE SKY

the earth it is possible to find the weight of the
earth's atmosphere, which is approximately six
quadrillion tonst or one-millionth of the mass of
the earth.

105

CHAPTER XV

HOW A LITTLE SPECTROSCOPE TELLS THE SECRET
OF LIGHT

TT IS rightly considered one of the greatest
••• achievements of science that a tiny ray of light
coming to us from the immeasurable depths of
space can be made to unfold the secrets of the com-
position and nature of the body from which it
emanates, whether it is gaseous or solid, highly
heated or comparatively cool, new or far advanced
in evolution, and even the amount and direction of
its motion.

The little instrument that accomplishes such
wonderful results is known as the spectroscope and
the field of study that it has opened to us is known
as spectrum analysis. The essential part of the
spectroscope is simply a glass prism, or chain of
prisms in some cases, or it may be a piece of plane
106

SPLENDORS OF THE SKY,

glass or speculum metal closely ruled with fine
lines, sometimes as many as 20,000 lines to the inch,
known as a diffraction grating. In each case the
object is to separate white light into the various
colors that enter into its composition. When a ray
of white light such as sunlight is passed through a
transparent medium denser than air, such as glass
or water, it is split up into its component parts,
which are rays of different colors and wave lengths.
We have then what is known as the spectrum. This
principle we have all seen illustrated in the rain-
bow, which is formed when rays of white light or
sunlight pass through falling drops of water, which
act as tiny prisms and split white light into the
rays of different wave lengths and color that com-
pose it. All the colors of the rainbow are familiar
to every one and they are the colors of the spec-
trum. If, as in the spectroscope, a ray of sunlight
is passed through a glass prism we see a ribbon of
variegated colors blending into each other grad-
ually. If the prism is so turned that the red will
appear at our left hand we shall see in order from
left to right — red, orange, yellow, green, blue, in-
digo and violet, arranged according to their respec-
tive wave lengths. The red rays have the greatest
101

SPLENDORS OF THE SKY

wave length and are the least bent from their course
and the violet are the shortest and so the most re-
fracted. The wave lengths of the visible spectrum
vary from .0008 millimeter for the red to .0004 for
the violet. When we consider that .0001 millimeter
is equivalent to 1-250,000 of an inch and that we
can measure a displacement of this amount in the
spectrum the wonderful accuracy of measurements
by this method is apparent.

Beyond the visible red rays we have the "infra
red" rays and beyond the violet rays the "ultra
violet" rays. The human eye is not sensitive to
these colors, but their presence has been detected
by photography, in the case of the ultra violet rays,
and by the heat produced by infra red rays, which
are sometimes spoken of as "heat rays." The pho-
tographic plate is particularly sensitive to the violet
end of the spectrum. Very much can be accom-
plished in spectrum analysis by means of the
photographed spectrum.

An examination of the spectrum produced by a
ray of sunlight, which is known as the solar spec-
trum, shows a great number of fine dark lines
crossing the solar spectrum vertically. These are
the absorption lines, sometimes called the Frauen-
108

SPLENDORS OF THE SKY

hofer lines, and it is these dark lines that tell us
so much of the temperature and constitution of
the sun.

Every chemical element when heated to vapori-
zation and every gas heated to incandescence has
its own characteristic spectrum, certain bright lines
that essentially belong to it alone and that always
appear in exactly the same position in the spec-
trum. The greater the heat the more intense the
lines appear, so the spectroscope can detect tem-
perature changes. No two elements can have the
same lines in the spectrum nor any lines in com-
mon. When a compound of sodium, for instance, is
heated to vaporization, two lines characteristic of
sodium appear in the yellow of the spectrum al-
ways in exactly the same position. They are the
characteristic lines of sodium, and if they appear
in the spectrum of a certain star we know that
sodium occurs in that star in a state of vaporiza-
tion. If, however, a still hotter source of light is
placed behind the vapor of sodium so as to shine
through it the sodium lines appear as dark lines
in the spectrum of the hotter light. Any other ele-
ment, of course, acts in the same way when placed
before a brighter light and the dark lines of the
109

SPLENDORS OF THE SKY

substance are then spoken of as absorption lines.
Take away the source of light beyond and they ap-
pear as bright lines again.

The dark lines that appear in the solar spectrum
are the lines of vaporized elements that surround
the hotter surface of the sun, and it has been
through comparison of these lines with the bright
lines produced by known terrestrial elements in the
laboratory that we have found that the sun con-
tains many elements that occur on the earth. It is
an interesting fact that at the time of total solar
eclipse, after the surface of the sun has been en-
tirely hidden by the moon and before the surround-
ing gaseous envelope has been covered, the dark
lines of the solar spectrum suddenly flash forth as
bright lines. This is what we should expect, for
when the hotter source of light beyond is removed,
the absorption lines appear as the bright lines of
vaporized elements shining by their own light.

There is a principle of spectrum analysis the
value of which can hardly be overestimated in con-
nection with the study of the heavens, for it has
opened an entirely new field of discovery only
secondary in importance to that opened up by the
discovery of the telescope. That is, if a body emit-
110

SPLENDORS OF THE SKY

ting light, such as a star or nebula, is in motion
either toward us or from us, this motion will show
in its spectrum. If the body approaches us the
wave lengths of the ray of light entering the spec-
troscope are of greater frequency and therefore
shortened in length and all the lines of the spec-
trum show a shifting toward the violet end of the
spectrum, and if the body is receding from us the
wave lengths are of less frequency and, so, longer
and all lines are shifted toward the red end of the
spectrum, and the amount of the shift measures
the velocity of the motion. This fact enables us
to confirm the time of rotation of different portions
of the sun's disk formerly determined by means of
sun spots. It also tells us that the stars are moving
and that the motion of a star in the line of sight
varies from a few miles a second to over 200 miles
a second in extreme cases. It is not usual, how-
ever, to find stellar motions greater than forty miles
a second in the line of sight though the actual mo-
tions may be considerably greater. It shows the
great accuracy of these measurements that stellar
motions as small as one-fifth of a mile a second can
be detected. The surprising fact has been indi-
cated by the spectroscope that the stars least
111

SPLENDORS OF THE SKY

advanced in evolution move the most slowly, and as
the age of the star increases the velocity increases.
A star starts in the beginning with hardly any mo-
tion and acquires increasing velocity. It is now
generally believed that stars form in the regions of
the Milky Way and as their velocity increases
they move further and further away from this
plane.

"We can no more than touch upon a few of the
many wonderful truths revealed to us by the spec-
troscope. Stars have been grouped into classes ac-
cording to their spectra. There is the Orion type,
often called the Helium type from the prominence
of the lines of that element in the spectra of such
stars. The Sirian type, named after its most prom-
inent member, Sirius, shows hydrogen lines in great
intensity. The Calcium type, named from charac-
teristic lines of calcium, shows intense hydrogen
lines as well. The Solar type, which includes our
own sun, has its spectrum crossed by numerous
dark metallic lines such as appear in the solar
spectrum, and also hydrogen lines. In the type
called K, which is next in evolution, the hydrogen
lines have become fainter than some of the metallic
lines. In the type last in evolution, composed of
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SPLENDORS OF THE SKY

dark reddish stars and known as type M, the spec-
trum is characterized by fhitings due to titanium
oxide. It is considered very remarkable that spec-
tra of this type are so dominated by this one sub-
stance. These types have been named in the gen-
erally accepted order of evolution ; a star may pass
in its life through all these different stages.
Earlier than the Orion stars occur, however, stars
of type O, called Wolf-Rayet stars, whose spectra
consist of bright bands on a faint, continuous back-
ground. These latter stars are all found in the
plane of the Milky Way and at great distances,
and are believed to come first in evolution. The
great Andromeda nebula shows a spectrum, in
which most of the lines of this type are present.

The Orion and Sirian stars, which come early
in evolution, are blue-white and white stars. The
solar type includes the yellow stars and the later
types the reddish stars.

In the study of our own sun, pressure, magnetism
and radiation are all detected and measured by
the spectroscope. Among double stars we are find-
ing, by means of the spectroscope, an ever-increas-
ing number that are so close together that they are
beyond the reach of the most powerful telescopes,
113

SPLENDORS OF THE SKY

but the shifting lines of the spectrum reveal the
mutual revolution of the two components.

In this modest little instrument we possess a key
to many mysteries of the heavens that would other-
wise be forever beyond our reach. It is little won-
der that the astronomy of the spectroscope is called
the "new astronomy" and by its means we hope to
obtain an ever-increasing knowledge of the uni-
verse.

114

CHAPTER XVI

SECRETS OF THE SUN REVEALED BY THE SPECTROSCOPE

•pKACTICALLY all that man knows of the phys-
•*• ical constitution of our sun, which is simply
one of the stars, has been discovered through
painstaking examination of several thousand fine
dark lines in the solar spectrum, spoken of usually
as the Frauenhofer lines.

These investigations have been carried on in con-
nection with extensive laboratory experiments with
the spectra of all the known elements found upon
our planet.

Not only the nature and distribution of the ele-
ments that exist in the sun 's atmosphere have been
determined in this way, but a number of very im-
portant additional facts have been ascertained as
well, such as the magnetic field existing in sun
spots and the amount of pressure prevailing at
115

SPLENDORS OF THE SKY

the sun's surface. All the various forms of solar
activity are constantly being recorded in the lines
of the solar spectrum and to interpret the evidence
correctly is the duty of the astronomer engaged in
solar research.

The solar spectrum consists of a continuous band
of variegated color crossed vertically by an enor-
mous number of fine dark lines, fully 14,000 of
which have been mapped and their wave lengths
determined with a high degree of accuracy.

It is, of course, the relative positions of these
dark lines in the spectrum that are important and
not the bright, continuous band of color upon which
they arc projected, and which owes its origin to the
intensely hot solar core of incandescent gases under
high pressure. The dark lines originate in the
cooler solar atmosphere lying just above the visible
solar surface and are in reality not dark except by
contrast. Remove the brilliant background and
they appear as bright lines. This is exactly what
occurs at the beginning of totality at the time of a
total eclipse of the sun when they produce what is
known as the "reversed" or flash spectrum.

As the moon passes before the sun the solar sur-
face is covered more and more until finally there
116

SPLENDORS OF THE SKY

comes a moment when the last slender crescent of
light disappears. The brilliant background has
been removed and the portion of the solar atmos-
phere lying just above the surface of the sun at
the rim shines forth by its own light. The lines of
the spectrum that are usually black on a bright
background are now brilliant against a background
that is black. This phenomenon is visible at the
eastern edge of the sun at the beginning of totality
and at the western edge at the end and is referred
to as the flash spectrum. It lasts but a moment,
as this lower solar envelope, spoken of as "the re-
versing layer" since it reverses the solar spectrum
at this time, is very shallow, and so is quickly cov-
ered by the moon.

It is possible to compute its depth from the
known motion of the moon and the duration of
flash spectrums and it is found to be about 500
miles. In this layer occur the dense metallic va-
pors that give the dark lines of the spectrum, which
are called absorption lines because they ab-
sorb from the light beyond exactly the same rays
of which they themselves consist. Since to each
chemical element belongs always the same definite
group of lines in the spectrum, unvarying in posi-
117

SPLENDORS OF THE SKY

tion even under a wide range of temperature and
pressure, it is possible to determine from the po-
sitions of the various lines the elements to which
they belong. By producing the spectra of all the
familiar terrestrial elements in the laboratory, by
heating them to incandescence in various ways and
passing their light through the spectroscope, it has
become possible to measure and map the lines of
all known substances and to identify them as far
as possible with the lines of the same elements
found in the sun's spectrum. Since the light from
the sun's interior gives the continuous band of
color it is the gases that compose the sun's atmos-
phere and not the sun's interior that are studied.
Thirty-eight terrestrial elements are known to
exist in the lower solar atmosphere. These are
chiefly the metallic elements and hydrogen and
helium. Carbon occurs only in compounds and free
oxygen has been detected with great difficulty.
Titanium oxide is found in abundance in sun spots.
Some of the heavier elements, such as gold and
mercury, are missing, but this may be due to the
fact that the heavier elements probably lie at a
greater solar depth and therefore do not appear in
a spectrum belonging to the higher levels,
118

SPLENDORS OF THE SKY

It is a peculiar fact that none of the "negative"
elements appear in the solar spectrum. The halo-
gen group, including such elements as chlorine and
bromine, the oxygen group including the import-
ant element sulphur and the nitrogen group are
not to be found in the sun, though nitrogen appears
in the form of cyanogen. The explanation has
been offered that the spectrum of an element is
sometimes entirely suppressed by a small amount
of another element. The spectral lines of the non-
metals are apt to be suppressed by the metallic
elements. It is well-known that helium does not
absorb the rays from the solar surface and does
not give a dark absorption line, as in the case with
all other known gases. This is in flat contra-
diction to one of the fundamental laws of spec-
trum analysis. This is simply another peculiarity
of this very unusual gas. It occurs in abundance
in the sun, however, and its characteristic bright
yellow line is in the flash spectrum and can always
be seen when the light of the photosphere is
screened off.

Of the fourteen thousand dark lines of the solar
spectrum that have been mapped, one-third are
1 ' telluric ' y lines originating in our own atmosphere
119

SPLENDORS OF THE SKY

and are due to absorption of the sun's rays by
gases in the earth's atmosphere, chiefly oxygen,
carbonic acid gas and water vapor.

The origin of about six thousand of the solar
lines is still undetermined or doubtful. Some of
these are extremely faint. Of course, many of
them may belong to a single element. There is
great disparity in the number of lines belonging to
the various elements. The spectrum of iron is
represented by more than two thousand lines in the
solar spectrum, calcium by about seventy-five and
lead by only one. The work of identifying the lines
of the solar spectrum is still going on and it is ex-
pected that all the doubtful and unknown lines
will be traced to their origin before many years.

Changes in solar temperature and pressure regis-
ter their effect upon the appearance of the lines
of the spectrum. Motion of the source of the light
toward or from the observer, as motion of the west
limb of the sun toward the earth and of the east
limb in the opposite direction due to the rotation
of the sun on its axis, causes a shift of all the spec-
tral lines toward either the violet or the red end
of the spectrum, according to a well known law of
spectrum analysis. The periods of the sun's ro-
120

SPLENDORS OF THE SKY

tation, varying according to latitude, have been
accurately determined from this shifting of the
dark lines of the spectrum.

By special contrivance light can be reflected from
the two limbs so that two spectra may be produced
simultaneously, the one from one limb immediately
above the one from the other. The effect of the
sun's rotation can then be determined very accu-
rately from the double displacement of the lines.
The lines originating in the earth's atmosphere
will not show this shift and can be readily identi-
fied at this time. Increase of pressure in the solar
atmosphere will broaden the lines and shift them
all slightly toward the red. The continuous spec-
trum that forms the background of the dark lines
is due to the light coming from the sun's interior
where the pressure is so great that the lines have
probably been broadened until they coalesce.

Dark absorption lines at times become tempor-
arily bright in the centre for all or part of their
length. This is spoken of as reversal of the lines,
and is due to a hotter source of light suddenly
being thrown in front of a cooler gas. This fre-
quently occurs when some solar eruption causes a
sudden upheaval of low lying, highly heated gases.
121

SPLENDORS OF THE SKY

It is often seen in the spectral lines of promi-
nences.

At times double reversals of lines are seen, par-
ticularly of the sodium and magnesium lines. In
such cases the bright line itself widens and a fine
dark line appears in the centre. This appears to
be due to large quantities of the vapor at great
density.

The dark lines of the spectrum often appear dis-
placed and distorted, due to a sudden upheaval of
gases and outbursts of solar activity in the vicinity
of prominences.

A most important effect frequently observed in
the vicinity of sun spots is that known as the
Zeeman effect. This is the splitting of a line into
two or more components of opposite polarity, due
to the presence of a magnetic field. It was from
observing this effect that Hale discovered the mag-
netic field existing in sun spots. There is a whirl-
ing or vortical motion in sun spot regions carrying
along electrically charged particles that produce
the magnetic field. In fact, it has been found re-
cently that the whole sun is in a magnetic field
whose poles agree very closely with the sun 's poles
of rotation, and it is also possible that the earth
122

SPLENDORS OF THE SKY

and sun may be in magnetic states as a result of
their rotation and that all rotating bodies are
magnetic.

It has been possible to touch upon only a very
few of the most important facts that have been
discovered from careful study of the dark lines of
the solar spectrum made with that most valuable
instrument, the spectroscope. The branch of solar
physics is probably the most fruitful of all fields
of astronomical research, and our knowledge of
the nature of the sun and its surroundings is in-
creasing rapidly.

123

CHAPTER XVII

THE SPOTS ON THE SUN

SUN spots appear singly and in groups in con-
stantly recurring cycles upon the surface of the
sun. Near what is known as the period of sun
spot maximum, the photosphere or visible solar sur-
face is never clear. It is often possible at such a
time to count as many as fifty spots occurring
singly or in groups. Large single spots are less
frequent than groups consisting of a fairly large
spot accompanied by a train of smaller ones. Spots
vary greatly in size. Isolated spots frequently at-
tain a diameter five times that of the earth, and
sun spot groups at times cover an area of more
than one-tenth of the sun's diameter.

The average duration of a sun spot is two or
three months, though some last only a few days.
They are carried across the solar disk from west
124

SPLENDORS OF THE SKY

to east, and the average time it takes a spot to per-
form a revolution is twenty-seven and one-fourth
days. Different spots show considerable difference
in time of rotation, as we should expect, for the
sun's period of rotation is not constant as is the
case with the earth, but varies greatly for different
solar latitudes. Spots, moreover, have slight mo-
tions of their own which affect their time of revo-
lution. A spot is visible continuously for about
two weeks, appearing at the western edge of the
sun and disappearing over the eastern edge, to re-
appear once more at the western limb after two
weeks have elapsed, provided it has not 'suffered
dissolution in the meantime. Spots often appear
and reappear for several successive solar rotations
with no marked change of form.

At times a sun spot will form in a single day,
again it will require days or even weeks for com-
plete development. Usually there is disturbance of
the solar surface for some time before the appear-
ance of a spot. Many brilliant faculae, which are
intensely bright flecks upon the sun's surface,
make their appearances, and among these are scat-
tered very small, black dots which gradually en-
large. Between the black djots appear grayish
125

SPLENDORS OF THE SKY

patches, which have the appearance of a veiled dark
mass. This veil gradually fades away and we see
the perfected spot. This consists of a dark central
portion or umbra and an extensive grayish penum-
bra. The black dots either coalesce with the prin-
cipal spot or disappear or go to form an attendant
train of smaller spots.

When a spot is formed it is usually roughly cir-
cular in form and remains without marked change
until it breaks up. When this occurs the surround-
ing solar surface seems to crowd in upon the pe-
numbra and bridges of light that are often much
brighter than the average solar surface span the
umbra or dark central portions. The spot disap-
pears as if overwhelmed and the disturbed surface
is again covered with the brilliant flecks or faculae
which are regions of intensely high temperature.
Frequently the disturbance breaks forth anew at
the same spot after a few days' interval and an-
other spot may appear exactly where the old one
disappeared. This appearance and disappearance
may be repeated several times. Occasionally a
large spot divides into two or more and the parts
seem to repel each other and fly asunder with a
velocity that may reach as high as a thousand miles
126

THE GREAT NEBULA IN ORION
(Photographed by Ritchey with the 2-ft. reflector of the Yerkes Observatory)

SPLENDORS OF THE SKY

an. hour. This repulsion probably arises from the
fa ct that a strong magnetic field exists in sun spots,
adjacent spots frequently being of opposite po-
larity.

When a sun spot is forming, eruptive promi-
nences appear in the immediate neighborhood.
These are upshooting jets of gases that attain a
height of 20,000 or 30,000 miles on the average.
Tiey are varied and beautiful in appearance and
change in form with great rapidity, often at a rate
oi 100 miles a second.

Sun spots are confined to certain definite zones
or belts upon the sun's surface. They are never
found at the equator or poles. In fact, their ap-
pearance beyond forty degrees north and south of
tie equator is extremely rare. They usually ap-
pear between ten degrees and thirty degrees north
and south latitudes, and in the long run appear as
frequently in one hemisphere as the other.

The periodicity of sun spots is one of the most in-
teresting and most puzzling facts concerning them.
Within a period whose average length is about
ebven years, sun spots go through a cycle of maxi-
mum and minimum appearance. At time of maxi-
mum spottedness the sun's surface is never free
127

SPLENDORS OF THE SKY

from spots; at the minimum weeks may pass with-
out the appearance of a single spot. Although the
average cycle is eleven years, individual periods
may vary greatly, running from seven to seventeen
years in duration. Attempts have been made to
show that a larger period of thirty-three and one-
third years exists, of which the smaller periods are
subdivisions. When we know the cause of the sun
spot cycle we shall have advanced far in the solu-
tion of the mystery of sun spots and all their num-
erous allied phenomena.

Sun spot spectra have been extensively studied
and much has been learned from this means of
investigation. They show the presence of strong
magnetic fields as well as a marked cooling of over-
lying gases, and the presence within spots of such
compounds as titanium oxide and calcium and
magnesium hydride. These compounds could only
form at comparatively low temperature and it is
assumed that sun spots are regions of cooler solar
temperature of about 3,500 degrees C., as com-
pared with 6,000 degrees C. for the remainder of
the photosphere.

The presence of the compounds above mentioned
gives the sun spot spectra their peculiar fluted ap-
128

SPLENDORS OF THE SKY

pearance, which is also seen in the red type of
stars. This is very significant when we consider
that the red stars are the older and cooler stars.
Are sun spots then one of the signs of the sun's
advancing age ? And will they increase in size and
importance as the sun grows older?

Sun spots, it is now believed, are manifestations
of some deep-lying disturbance that is of far-reach-
ing importance. Many phenomena go through
cycles of change in keeping with the sun spot cycle.
Among these are magnetic storms and magnetic
disturbances upon the earth which are closely de-
pendent upon the sun spot period. Severe mag-
netic storms upon the earth occur at a time when
the sun's face is strongly spotted, and displays of
northern and southern lights are also most marked
at this time. The general surface air temperature
of the earth is lower by about a degree at the time
of maximum spottedness of the sun.

One of the most marked effects of the sun spot
cycle is the form of the solar corona, which is only
visible at time of total solar eclipse. At the time
of a maximum sun spot period the corona is an
evenly developed halo surrounding the sun. At
the sun spot minimum it shows equatorial stream-
129

SPLENDORS OF THE SKY

ers that often extend to a distance of several times
the sun's diameter, while on either side of the
solar poles only short filaments of light appear.
So decided are these changes in the form of the
corona with the change in the sun spot period that
the two types are spoken of as ' i the sun spot max-
imum corona" and "the sun spot minimum co-
rona."

As to what causes these periodic outbreaks upon
the solar surface we are still in the dark. Some
astronomers believe they are caused by external
influences such as periodic returns of swarms of
meteors or returns of certain planetary configura-
tions. Careful and long-continued observations
seem to show that sun spots are rather the result of
internal disturbances which cause a transference of
solar matter from within outward in a cyclonic mo-
tion, which has been compared in form to that of
whirling waterspouts at sea. The central stem
forms the umbra and the outspreading gases the
penumbra. There is a tendency for a vacuum to
form in the centre of the whirl and into this is
drawn the overlying gases, chiefly hydrogen.

The rapid expansion of gases as they approach
the solar surface from within causes a sudden cool-
130

SPLENDORS OF THE SKY

ing, which accounts for the comparatively low
temperature in spots and the formation of such
solids as titanium oxide and the hydrides of cal-
cium and magnesium. These dissimilar substances,
it is believed, give rise by friction to the magnetic
field which is known to be a feature of sun spots.

It is hoped that continued solar research will
make known in time the cause of these peculiar
periodic disturbances that are so far reaching in
their effect.

131

CHAPTER XVIII

SOLAR EXPLOSIONS

\ MOST interesting discovery has been made
•**• within the past few years of the sudden, but
rather infrequent, appearance at the surface of
the sun of hydrogen " bombs," as they have been
called.

These "bombs'* are apparently violent explo-
sions of highly heated hydrogen gas in regions of
great solar activity. At times, according to Dr.
Ellerman, of the Mount Wilson Observatory,
who discovered them, they will follow one another
like balls of a Roman candle at intervals of ten or
twenty minutes. The duration of the explosion is
usually about two or three minutes, more rarely
five or ten minutes. The "bombs" generally ap-
pear on the edge or at one side of active sun spot
groups that are developing and are composed of
132

SPLENDORS OF THE SKY

many members. Repeated explosions often occur
almost exactly in the same place.

The presence of the "bombs" is revealed by the
appearance of two intensely brilliant narrow bands
of nearly uniform width on either side of the dark
absorption line of hydrogen that is associated with
the higher solar atmosphere. The fact that the
dark line itself is not interfered with nor any
other of the absorption lines belonging to the va-
rious strata of the sun's atmosphere shows that
the explosions occur considerably below the chro-
mosphere, the lowest, densest layer of the solar
envelopes, in which are to be found the majority
of all the gaseous elements that compose the sun's
atmosphere.

The area covered by the explosion is so small
that the bombs can only be seen with a large solar
image and under fine "seeing" condition. Dr.
Ellerman first saw the two brilliant bands sud-
denly appear one on each side of the dark absorp-
tion line of hydrogen in September, 1915, while he
was observing the dark line for distortions and
reversals in connection with an active sun spot
group.

Within two minutes the bright bands disap-
133

SPLENDORS OF THE SKY

peared and were not seen again. A month later
additional explosions were recorded visually and
photographically.

The phenomenon of the solar hydrogen "bombs"
has now been recognized for some time as an estab-
lished feature of solar activity. The close associa-
tion of hydrogen with sun spots in the form of
vast eruptive prominences of highly heated hydro-
gen and the descent of cooler hydrogen from the
upper solar atmosphere into the vortices of sun
spots has long been known.

A most valuable instrument employed in study-
ing the distribution of the various gases in the
sun's atmosphere is the spectroheliograph, which is
simply a moving spectroscope timed to travel over
the 'solar disk at a uniform rate with the slit of the
instrument so adjusted that the light from only
one line of an element in the solar spectrum is ad-
mitted to the eye or the photographic plate.

In this way the distribution of the vapors of in-
candescent hydrogen or calcium, iron or any other
element at different levels of the sun's atmosphere
can be studied in great detail as well as the con-
nection of these elements with sun spots and other
solar phenomena. When the sun is viewed with
134

SPLENDORS OF THE SKY

the spectroheliograph in the light of a single spec-
tral line of hydrogen it is possible to detect the
presence of the flames of incandescent hydrogen in
the prominences by their projection on the sun's
disk as irregular dark patches or streaks as well as
to study their infinite variety of forms when the
slit of the instrument is set at the edge of the sun's
disk.

When the surface of the sun is viewed telescopic-
ally, it presents a peculiar mottled appearance, or
rice-grained structure, as it is called. The spec-
troheliograph shows that this same structure is
found in the chromosphere and in the higher solar
atmosphere. The rice grains of the sun's surface
are intensely brilliant flecks of light, each com-
posed of a great number of minute granules or
mere points of light.

The rice grains are usually about 400 miles in
diameter, while the granules measure less than ten
miles across. In sun spots these minute granules
are replaced by minute filaments that group them-
selves into the familiar " thatch straw" structure
of the penumbra that surrounds the umbra or dark
central portion of sun spots.

It is now believed that the granules and the fila-
135

SPLENDORS OF THE SKY

ments are all the same. Columns of highly heated
gases arise by convection from the sun's interior.
The granules are cross section views of these ver-
tical columns. In the vicinity of sun spots the
ascending columns of gases are drawn into posi-
tions more or less at right angles to their normal
positions by the whirling vortical motion existing
in sun spot regions, and they then appear as the
long, slender filaments that form the thatch straw
structure of the penumbra of sun spots.

Now the spectroheliograph shows in the layers
of the sun's atmosphere above the photosphere the
same peculiar structure. The "flocculi" of hydro-
gen and calcium resemble in appearance the rice
grains of the sun's surface. These flocculi are
ascending columns of expanding and cooling hy-
drogen and calcium vapors that rise far above the
level of the photosphere, or visible surface of the
sun.

It is an interesting fact that different spectral
lines of an element usually are associated with dif-
ferent levels of the sun 's atmosphere. The element
hydrogen, for instance, has lines in the red end of
the spectrum and lines in the violet. The red rays
of any element in the sun rise normally to a much
136

SPLENDORS OF THE SKY

higher level than the violet rays, for the rays of
shortest wave length, violet and ultra-violet rays
are more liable to be trapped in the denser lower
atmosphere of the sun, while the longer red rays
escape.

By setting the spectroheliograph on the violet
lines of hydrogen the distribution of hydrogen in
the lower levels can be studied, and by setting on
the hydrogen lines in the red the scarlet flames of
incandescent hydrogen gas in the prominences that
reach to heights of 100,000 or 200,000 miles above
the photosphere can be exhaustively examined.

It is possible that there are rays of extremely
short wave length in the sun's interior that never
reach the photosphere, but are imprisoned far be-
neath, while the red, orange and green rays of the
various elements escape readily to the surface and
the higher atmosphere of the sun. As a result the
sun presents a decidedly yellowish hue to the eye.

The calcium flocculi representing highly heated
columns of calcium gas are bright flecks on a dark
background, for they are at a higher temperature
than the surrounding gases, which appear dark by
contrast, but still higher up, where hydrogen alone
persists, the hydrogen flocculi appear dark against
137

SPLENDORS OF THE SKY

a bright background of diffused gases, for at the
reduced temperature of the higher level the ex-
panded and cooled hydrogen shows its presence by
absorption.

Photographs of these upper regions taken with
the slit of the spectroscope set on the hydrogen line
characteristic of this elevation show most interest-
ingly the peculiar distribution of hydrogen gas
here. Irregular dark streaks projected upon the
sun's disk show the presence of eruptive or quies-
cent prominences. Above sun spots or sun spot
groups the hydrogen flocculi are curved either in
clockwise or counter-clockwise direction, showing
that a whirling motion of the hydrogen gas exists
and that it is being sucked downward with a cy-
clonic motion into the umbrae of the sun spots that
lie at the level of the solar surface.

The revelations of the spectroheliograph are,
therefore, rich in information concerning the dis-
tribution and behavior of the gases that are found
at the surface of the sun and in all the different
layers of its atmosphere.

It pictures a sun of explosions, eruptions and
ceaseless activity. Countless columns of highly
heated gases of many elements rise to the surface
138

SPLENDORS OF THE SKY

and penetrate in some instances even into the
higher solar atmosphere, the lightest elements at-
taining the greatest heights, later to descend in
cooler streams or cyclonic whirls to the photosphere
and the sun spot regions.

139

CHAPTER XIX

SOME RECENT TOTAL SOLAR ECLIPSES AND THEIR VALUE
TO ASTRONOMY

CLIPS ES as well as comets were always hailed
in ancient times with dire misgivings, and
even at the present day the uneducated and
ignorant of all lands are not entirely free from
fear and superstition regarding these celestial hap-
penings. Up to a few centuries ago it was firmly
believed that such phenomena heralded some
ominous change and there are instances in history
of abandonment of certain enterprises and even
cessation* of battles and a peace hastily concluded
due to the sudden darkening of the sun's face.
In modern times, on the contrary, we find scientists
bending every effort to observe all total eclipses
of the sun in whatever portion of the world they
may chance to fall that they may extend their
14Q

SPLENDORS OF THE SKY

knowledge of the wonderful physical constitution
of our sun and its mysterious coronal halo. To
obtain observations during a few fleeting moments
many hardships have been undergone by eclipse
expeditions. Many disappointments have also
been experienced in connection with this work.

The French astronomer Janssen escaped from
Paris in a balloon at the time of the siege of Paris
in 1870, carrying the essential parts of his instru-
ments with him for the purpose of observing the
total eclipse of the sun visible that year in Spain
and Africa, only to be defeated by clouds.

War as well as clouds has been the enemy of
many an eclipse expedition. At the beginning of
1914 elaborate plans were well advanced in many
lands for observation of the total eclipse of Aug. 21,
1914, visible in Europe from Norway and Sweden
through Russia to Persia, with a duration of about
two minutes. All the leading countries of Europe,
Argentina and the United States sent eclipse ex-
peditions to Russia in the neighborhood of Riga
and Kiev. Many expeditions were in the field set-
ting up complicated photographic and spectro-
scopic outfits and practising preliminary drills that
all might go smoothly during the critical moments,
141

SPLENDORS OF THE SKY

even as the armies of Europe were mobilizing for
the greatest war in the history of the world. A
few parties were successful in spite of war and
generally prevailing clouds, but the majority were
either turned back before reaching their destina-
tion or experienced extreme difficulty in returning
to their homes. Several German observers were
detained as prisoners of war in Russia. The Lick
Observatory expedition was compelled to return by
way of Moscow, Finland and Sweden instead of by
way of Berlin and Paris, as was originally planned,
while their instruments were kept in Russia for
nearly four years.

The first American eclipse expedition ever
formed was sent to Penobscot in the War of the
American Revolution. The first total eclipse to be
observed scientifically to any extent in North
America was the eclipse of July 18, 1860. Three
American observers, including Prof. Simon New-
comb, the noted American astronomer, penetrated
to the banks of the Saskatchewan to observe this
eclipse, while the astronomer, Gilliss traveled to
Washington Territory by way of Panama for the
same purpose, and was amply rewarded by ex-
cellent views of the solar prominences and the
142

SPLENDORS OF THE SKY

corona. Another American expedition sent to
Labrador was defeated by clouds. From that date
to the present time American eclipse expeditions
have been sent to the path of totality of every
important solar eclipse, whether in Europe, Asia,
Africa or South America.

The eclipse of the 8th of June, 1918, was a
return of the total eclipse of May 28, 1900, so suc-
cessfully observed by a large number of eclipse
expeditions in the Southern States from New
Orleans to Norfolk. After an interval of eighteen
years, eleven and one-third days, which is spoken
of as the eclipse Saros, the earth, sun and moon
returned to practically the same relative positions
in the heavens and all the circumstances of the
previous eclipse are repeated except for the
fact that the fraction of a day in the period
causes the eclipse to fall 120 degrees westward of
its former position, the amount of the earth's rota-
tion on its axis in this interval of time. In conse-
quence a different portion of the earth's surface is
visited by each returning eclipse of a given series.
The eclipse of May 17, 1882, lasting only one minute
and a half, but observed with great success by
many eclipse expeditions in Egypt on the banks
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SPLENDORS OF THE SKY

of the Nile, belongs to this same eclipse family.
The next return of the eclipse of June 8 will fall
upon June 19, 1936, and its path will extend from
the Mediterranean through southern Russia and
Asia to the Pacific coast.

Since the path of totality of the eclipse of June 8,
1918, passed diagonally across the United States
from Washington to Florida, eclipse expeditions
were sent to the central line from nearly all the
leading observatories in the country. No foreign
expeditions were in the field on account of the war
and many American astronomers were unable to
observe the eclipse for the same reason.

Since it has now become possible to study the
solar prominences without the aid of total eclipses
and since the search for intra-mercurial planets
appears to yield negative results, scientific interest
has centred of late years chiefly upon the elusive
coronal light, its nature and its cause and the
character of the peculiar unknown gas coronium
of which it is largely composed. Much is to be
expected from future investigations along this line,
but progress is necessarily slow, for so faint is
the coronal light that the least percentage of direct
sunlight completely masks it. So it is only when
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SPLENDORS OF THE SKY

the friendly moon interposes between the earth
and sun and completely hides the solar surface
that the beautiful pearly radiance of the corona
may be seen.

According to the reports of astronomers who
observed the eclipse highly satisfactory results were
obtained by many of the eclipse parties stationed
between Washington and Kansas despite the fact
that clouds gathered all along the path of totality
within the United States. The success of the ma-
jority of the expeditions is to be attributed to
breaks in the overhanging clouds occurring just at
the critical time.

According to the report of Prof. W. W. Camp-
bell, director of the Lick Observatory, who was in
charge of the Crocker eclipse expedition at Golden-
dale, Wash., observers at this station were pre-
paring to accept complete defeat from dense clouds
that overspread the sky from midnight of June 7
to past midnight of June 8, when within less than
one minute of total eclipse a sudden break in the
clouds uncovered an intensely blue strip of sky
and the thin solar crescent. The entire eclipse
programme was most unexpectedly carried out with
complete success.

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SPLENDORS OF THE SKY

Less than one minute after the end of totality
clouds once more covered the scene of the phe-
nomenon. The " seeing " at the critical time was
magnificent and the expedition became almost by a
miracle the most successful expedition ever sent
out from the Lick Observatory.

Twenty-six excellent photographs of the corona
were taken at Goldendale, ten with the forty-foot
camera on a large scale and eight each with a
forty-eight-inch coronal camera of three-inch aper-
ture and an eleven-inch coronal camera designed
for landscape work. The last two cameras were
suitable for showing the general outline and form
of the corona and the extent of the streamers. The
longest coronal streamers recorded at Goldendale
were approximately three solar diameters, or two
and one-half million miles, in length.

Six spectroscopic instruments mounted on a
single polar axis registered valuable spectra of the
corona and prominences, as well as of the chromo-
sphere or lower solar atmosphere.

The corona was particularly beautiful in form,

belonging to the variety known as a "petal-formed"

corona, a type occasionally noted in past eclipses.

The "petals" are the result of rifts in the coronal

146

SPLENDORS OF THE SKY

streamers and the crossing of curved rays. Seven
distinct petals were noted in the June eclipse.

Many observers described the corona as unusu-
ally brilliant and of an intense blue-white color.
In shape it was roughly triangular, the long
streamers to the east of the sun forming the apex
and the more evenly distributed streamers to the
west the base of the triangle.

The spectrum of the inner corona was "continu-
ous/* that is a continuous band of variegated color
with no dark absorption lines, showing that It
shone by its own inherent light and not by re-
flected sunlight. The outlying portions of tne
corona showed the faint absorption lines of the
solar atmosphere and therefore it was evident that
part of its brightness was due to reflected light
from the sun.

At least five unidentified bright lines were found
in the coronal spectrum and their wave-lengths
were measured, while the existence of seven other
bright coronal lines was suspected. The nature of
the element or elements connected with these lines
is undetermined, though several of the lines doubt-
less belong to the unknown element coronium.

The wave-length of the characteristic green line
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SPLENDORS OF THE SKY

of coronium was accurately measured from spec-
troscopic observations obtained during this eclipse,
which will aid greatly in its future identification.

The chromosphere, appearing as an extremely
narrow orange-colored rim of light surrounding the
sun and composed of incandescent gases of many
metallic elements, contrasted beautifully with the
pearly light of the corona tinged with the green
rays of the unknown coronium whose nature as-
tronomers are most anxious to discover from ob-
servations obtained during total eclipses of the sun.

Rising from the chromosphere are usually seen
during totality a number of "prominences," up-
shooting flames of incandescent hydrogen gas of a
deep scarlet hue. These outbursts of incandescent
gases from the dense lower strata of the solar at-
mosphere are at times very conspicuous and add
to the weird beauty of this unusual scene.

Even to the unaided eye the prominences of
June 8, 1918, were a most beautiful feature of
totality. Three huge blood red prominences, vary-
ing from 45,000 to 60,000 miles in height, were
visible 120 degrees apart. Though they were not
higher than the average, their structure was ex-
tremely interesting. One of these on the west edge
148

SPLENDORS OF THE SKY

of the sun was likened to the skeleton of some
prehistoric monster. A number of other minor
prominences were visible, and the north and south
poles of the sun chanced to be marked by two
bright prominences.

Several of the prominences were capped in a
most peculiar manner by curved coronal rays re-
sembling Gothic arches. The apexes of several of
these arches lay at a distance of fully 200,000 miles
above the solar surface. There appeared to be
some connection between the coronal arches and
the prominences. Doubtless the same force that
caused the upheaval of the gases composing the
prominences also produced the peculiar coronal
caps above them.

The coloring of the solar surroundings during
totality of the June eclipse has been described by
those who were privileged to observe it as gorgeous
beyond description. The deep orange tinge of the
chromosphere, contrasting with the intensely bril-
liant blue-white light of the coronal rays curved
mto beautiful petal-like formations, and the huge
blood red prominences presented a weird effect
never to be forgotten.

The great value of the next total solar eclipse,
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SPLENDORS OF THE SKY

that of May 29, 1919, lay both in its extraordinary
duration, amounting to nearly seven minutes at
maximum and far exceeding the average totality of
three minutes, and also in the fact that the eclipsed
sun was to be in a field particularly rich in stars,
midway between the Hyades and the Pleiades, a
position unusually favorable for testing the new
theories bearing on the nature of light and the
influence of the sun's gravitational and magnetic
field upon the path of a ray of light.

The belt of totality in this eclipse started on
the western coast of South America, the boundary
between Chile and Peru falling nearly on the cen-
tral line, and the northern limit of totality passing
only a few miles south of the Harvard College
observatory station at Arequipa, Peru.

Here the sun rose partially eclipsed, so it was
not expected that valuable observations would be
obtained with the sun so close to the horizon.
Passing over the towns of La Paz and Trinidad in
Bolivia, the path of totality entered Brazil, crossed
to the Atlantic Ocean at a point about three de-
grees south of the equator, passing almost centrally
over the towns of Caxias and Sobral, where the
duration was to be over five minutes, and then
150

SPLENDORS OF THE SKY

crossed the Atlantic Ocean to Cape Palmas, Liberia.

At St. Paul's Rocks in mid- Atlantic, at latitude
one degree north and longitude thirty degrees west,
the total phase was to last more than six minutes.
Bending southward from Liberia the path of total
eclipse passed over He Principe, or Prince's Island,
in the Gulf of Guinea, and Libreville in the French
Congo; thence across the African continent to the
Indian Ocean, the sun setting partially eclipsed
over the island of Madagascar.

British astronomers organized two eclipse expe-
ditions to observe this eclipse. Both expeditions
were equipped at the Eoyal Observatory at Green-
wich and left England about the middle of March,
one under Astronomers Crommelin and Davidson
for Sobral in northern Brazil, and the other, under
Prof. Eddington and Mr. Cottingham, for He Prin-
cipe in the Gulf of Guinea. At both stations the
total phase of the eclipse was to last more than five
minutes, and it was the plan of the observers to
concentrate all their efforts on testing the new
theories of light and the effect of gravitation upon
the course of a ray of light.

The Bureau of Terrestrial Magnetism of the
Carnegie Institute, under the directorship of
151

SPLENDORS OF THE SKY

Dr. L. A. Bauer, made extensive plans for mag-
netic and other allied observations of this eclipse.
Dr. Bauer left for England early in March, where
he organized an expedition to be stationed either
at He Principe or Libreville in the French Congo.
From there he proceeded to South America to
arrange for similar observations near Sobral, as
well as at a number of stations outside the belt of
totality. Various magnetic observatories, institu-
tions and individuals offered their co-operation for
this purpose.

Dr. C. G. Abbot, director of the astrophysical
observatory of the Smithsonian Institution, left
Washington the first of May for South America
to observe the eclipse near Sobral, which was the
chief station for observations on this continent.
The eclipse was to occur in the early morning at
this point, mid-totality coming shortly after 9
o'clock, while at Libreville, in the French Congo,
totality was to occur shortly before 3 o'clock in
the afternoon, local time.

The problem that the observers of this eclipse

were anxious to solve is whether or not light obeys

the laws of gravitation and is deflected from its

course upon entering the field of the sun's attrac-

152

SPLENDORS OF THE SKY

tion. Prof. Eddington, who was to observe the
eclipse in the French Congo, characterized it as the
problem of " weighing light."

According to the most recent theories light can
no longer be regarded as an elastic wave motion
of the universal ether that has been assumed to
pervade all space, but rather as consisting of widely
separated centres of energy whose particles vibrate
singly.

It is known that light exerts pressure and has
a finite velocity of 186,000 miles per second, and
therefore it is reasonable to assume that it pos-
sesses mass, momentum and, in the vicinity of a
strongly attractive body such as the sun, appre-
ciable weight, provided it obeys the laws of gravi-
tation. It was, therefore, to see if light is com-
posed of material particles obeying the Newtonian
law of gravitation that this eclipse was to be ob-
served.

It is possible to determine just how far particles
of matter coming from infinite space, in this in-
stance rays of light from distant stars moving with
a velocity of 186,000 miles per second, will be de-
flected from their course upon entering the field
of the sun's attraction, just as one can trace the
153

SPLENDORS OF THE SKY

path of a comet or meteor under the same con-
ditions.

It can be shown that the path of any such par-
ticle will have the form of a hyperbola con-
cave toward the sun and that the nearer the par-
ticles or light rays come to the sun's edge the
greater will be the curvature of the paths and the
greater the apparent displacement of the stars
away from the sun. For a ray of star light just
grazing the eclge of the sun it has been found that
a displacement of nearly one second of arc in the
star's position Is to be looked for if light obeys
the law of gravitation. This would be the greatest
displacement, for the nearer the rays pass to the
sun the more strongly they are attracted and the
more they are deflected from their course.

Obviously stars near the sun are invisible ordi-
narily. It is only during a total eclipse of the sun
when the stars shine forth as on a moonlight night
that it becomes possible to " weigh light" from
observations of the stars in the vicinity of the sun.

During this eclipse, it was expected at least thir-
teen stars would be visible close to the sun's posi-
tion. If displacements in the normal positions of
all of these stars were observed and if the displace-
154

SPLENDORS OF THE SKY

merits were greater the nearer the star came to the
sun by the amount required by the theory it would
be strong evidence in favor of the new theory that
light possesses* mass and weight and obeys the law
of gravitation.

The uncertainties attending observations of such
a nature are necessarily great. Aside from uncer-
tainties as to weather conditions there is the pos-
sibility that the solar corona might affect the star
positions, possibly refracting or blurring the images
of the stars and thereby introducing errors in the
measurements.

Errors of instruments must also be reduced to a
minimum to make possible accurate measurements
of these angles of displacement that, if existent,
scarcely exceed the parallaxes of the nearest stars.

The expeditions fitted at the Royal Observatory
of England expected to use the astrographic tele-
scope employed for cataloguing the positions of
the stars by photography, and it planned to make
the exposures of the photographic plates of ten
seconds duration. Comparisons of the positions of
the thirteen stars obtained during the eclipse with
the normal positions of these stars obtained when
the sun is in another part of the heavens should
155

SPLENDORS OF THE SKY

show the displacement due to the sun's influence
on the path of a ray of light, if it exists.

It is also possible to test at the same time the
noted Einstein theory of relativity that is the
subject of so much discussion at the present time.
According to this theory the velocity of light is
less in a strong gravitational field than it is in a
vacuum, and the displacement of the light from the
stars that passed through the field of the sun's influ-
ence comes out twice-that indicated by the first
theory.

It was difficult to obtain any information bear-
ing on these problems of light and gravitation
during the United States eclipse of June 8, 1918,
owing to the fact that the sun was at that time in
a field of very few stars.

The results of the observations of this eclipse are
not yet available but it is hoped that some of the
expeditions were successful in obtaining photo-
graphs that will be of value in solving this unique
problem of weighing light.

156

CHAPTER XX

ARE THERE OTHER PLANET WORLDS?

TF IT were possible for man to view the solar sys-
••• tern from the distance of the nearest star, our
glorious orb of day would appear as a first magni-
tude star, very similar to beautiful Capella, the
star of yellow hue that shines so conspicuously
near the meridian in northern skies in the early
evening hours of February.

If our greatest telescopes could be turned upon
the sun at this distance, the existence of his planet
family would never be suspected. Jupiter, the
greatest of the satellites, would be a star of the
twenty-first magnitude, shining by reflected light
only and situated but five seconds of arc distant
from the sun. When we consider that the most
powerful telescope in existence cannot show stars
below the twenty-first magnitude, even under the

157

SPLENDORS OF THE SKY

most favorable circumstances, the impossibility of
detecting even the greatest of the sun's family at
this distance is clearly evident.

The least distance that the unaided eye is able
to distinguish between two stellar objects is more
than 200 seconds of arc, so even if Jupiter shone
with a lustre equal to that of the sun the two would
appear as one star to the naked eye at the distance
of the nearest star. As,to the other planets: be-
fore the bounds of the solar system are passed,
Mercury, Venus, Earth and Mars sink into invisi-
bility, mere cosmic specks lost in the rays of a sun
that is rapidly assuming a starlike appearance
even at this distance.

We have likened the aspect of our sun at the dis-
tance of the nearest star, that is, at a distance of
only four light years, to the brilliant Capella, and
spoken of the total invisibility of its greatest satel-
lite, the mighty Jupiter, at this distance. How
would our glorious sun appear if it were situated
at the same distance from us as this conspicuous
star of winter skies forty light years away?

Instead of a brilliant first magnitude star we
would barely see an insignificant point of light of
the fifth magnitude, one-seventieth as bright as
158

SPLENDORS OF THE SKY

Capella and near the limit of visibility for the un-
aided eye. And yet Capella is not very far away
as star distances go in a sidereal universe some
300,000 light years in extent. Ten thousand light
years away great telescopes could not pick up the
tiny speck of light representing our sun among
the innumerable hosts of the universe.

The inconceivably great distances separating the
various suns that compose our universe render ab-
solutely hopeless any attempt to investigate the
planet families of other suns, if such exist, and we
very reasonably suspect that other planet worlds
do exist.

There are many stars in the stellar system that
closely resemble our own. So the spectroscope tells
us. Our sun is but one of the yellow stars. Line
by line its spectrum is reproduced in many a star
that is evidently composed of the same elements at
practically the same stage of stellar evolution. If
one member of this group is, to our knowledge, at-
tended by a planet family, we can hardly assume
that the reverse is true of all other stars of the
same type. Inability to detect the presence of
such worlds does not disprove their existence.

Possibly the day may come when some device at
159

SPLENDORS OF THE SKY

present unknown, as the spectroscope was less than
one hundred years ago, may accomplish as wonder-
ful results in the detection of dark bodies in the
universe, whether sun-like or planetary in size, as
the spectroscope has in the detection of dark and
light suns physically associated in double or mul-
tiple systems.

It is the spectroscope that tells us that beautiful
Capella is not a single star, such as our own sun,
but belongs to a star system composed of two bright
stars, each approximately equal in mass to our own
sun, that revolve around a common centre of grav-
ity in about one hundred days and are separated
from each other by a distance of about fifty million
miles.

It is now well known that a large proportion of
the stars are not single suns, but belong to systems
of two, three or more suns in revolution around a
common centre of gravity. The spectroscope tells
us that some of these bodies are dark. They make
known their presence only by the disturbance they
produce in the motion of the bright stars with
which they are associated. The fact that they can
produce such disturbances proves that they are of
sun-like dimensions and not planets. They are
160

SPLENDORS OF THE SKY

dark either because they are extinct through old
age or because they are, for some mysterious rea-
son, imperfect radiators of light.

A satellite such as Jupiter that possesses only
about one-thousandth of the mass of the sun it en-
circles could never appreciably affect the motion
of its ruler. The spectroscope would not reveal the
presence of such a modest attendant, though it
possesses more than 300 times the mass and 1,300
times the volume of our planet Earth. Yet small
planetary bodies may, for all we know, be members
of double and multiple star systems. There may
be all gradations in such systems from dark bodies
of sun-like mass, capable of revealing their pres-
ence to observers hundreds or even thousands of
light years distant, down to hopelessly obscure
planets or planetoids such as our ringed Saturn,
mighty Jupiter, modest planet Earth, or the num-
berless asteroids of the sun's family. The masses
of celestial bodies can only be found through their
attraction for other bodies. It is impossible to
know anything definite about the masses of solitary
stars since they lie so far apart.

Systems of connected stars, on the other hand,
through the attraction of the various members for
161

SPLENDORS OF THE SKY

each other, furnish a method for determining the
combined masses of the stars in terms of our sun's
mass when their distance from the earth is known.
One of the interesting results of the investigations
of the masses of these binary systems is to show that
our sun is an average star. Though there are
giants in the universe such #s Arcturus or Cano-
pus or Rigel that dwarf our sun into insignificance,
and though nearly all the stars visible to the naked
eye are far more brilliant than our luminary, they
represent the exceptional stars. Among the tele-
scopic stars, the countless hosts that go to form the
sidereal universe, our sun is about the average in
size and importance and in no respect remarkable
unless we assume that, for some mysterious reason,
the rays of this one alone are capable of fostering
varied and multiple forms of life upon attendant
planets.

Binary star systems often present strange and
unexplained variations of light. In some instances
light variations are due to the temporary eclipse of
one member of the system by the other, as in the
noted Algol system. There are, on the other hand,
light changes in other binary stars not so easily
explainable. The Cepheid variables, as they are
162

SPLENDORS OF THE rSKY

called, have so far defied all attempts at a satis-
factory explanation of their peculiar behavior.
They are characterized by a periodic variation of
light of short duration. The entire cycle of change
is usually accomplished in a few days, in some stars
in a few hours. A very rapid rise to maximum
brightness is followed by a prolonged drop to mini-
mum that is sometimes interrupted by a weak at-
tempt at an increase of brightness. This cycle of
change is repeated continuously with clock-like pre-
cision.

Many explanations of the peculiar behavior of
these stars have been suggested, though none fit all
the requirements. According to one theory the
peculiar light variations are due to internal oscil-
lations of the stars resulting from collisions with
planetary masses.

There are also the remarkable cluster variables
found in some of the noted globular clusters com-
posed of thousands of stars. They resemble the
Cepheids in the nature of their light variations,
though the periods are extremely short. The cycle
of change is usually accomplished in less than
twenty-four hours. Some stars wax while others
wane, each star keeping strictly to its own period,
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SPLENDORS OF THE SKY

entirely independent of other stars in the same
cluster.
This independence of each other is not so strange

when we consider that the individual stars in the

\

globular clusters are separated by distances com-
parable to the distance that separates our solar
system from the nearest stars and that ample room
is furnished each star for the possession of exten-
sive satellite families without being crowded by too
close stellar neighbors. Why some few stars in a
globular cluster should show this unaccountable
periodic flickering of light while the majority shine
with clear and steady rays is another of the unex-
plained mysteries of this wonderful universe of
which we form such a humble part.

164

CHAPTER XXI

DRIFT OP THE STAR STREAMS

THE sun, as is now well known, travels through
the universe at the rate of twelve miles a
second, or more than 1,000,000 miles a day. In a
year it passes over four times the distance from the
earth to the sun and after an interval of nearly
16,000 years has journeyed the same distance
through space that light travels in one year.

The earth and other planets, of course, share this
motion of their ruler, since the solar system moves
as a unit with the relative motions and positions of
its various members unaffected by the translation
of the whole system through space. The revolu-
tion of the planets around the sun, combined with
the motion of the system as a whole, causes their
paths through space to assume the form of cork-
screw spirals.

165

SPLENDORS OF THE SKY

In the past five thousand years practically no
changes appreciable to the naked eye have taken
place in the forms of the constellations or the
brightness of the stajs due to this motion of the
sun. After an interval of one hundred thousand
years, however, which is less than the period man
has been known to exist upon this planet, the in-
dividual motions of the stars combined with the
sun's advance through the universe begins to no-
ticeably alter the appearance of the constellations
and the brightness of the nearer stars.

[n this time the sun travels between six and seven
light years, which is more than the distance that
separates us from a few of the nearer stars. From
the birth of a star to its extinction many journeys
to and fro from one end to the other of the stellar
system may be possible if the extent of the system
of the stars to which we belong is limited in diam-
eter.

In four hundred million years, a less time than
has elapsed since the formation of the earth's sur-
face crust, according to some geologists, the sun
has journeyed so far through our stellar system
that its light will take 25,000 years to retrace the
path. In other words the sun has travelled in this
16S

SPLENDORS OF THE SKY

period 25,000 light years, which is sufficient to have
brought it from far-distant star clouds of the Milky
Way to its present position.

During this tremendous interval of time what
portions of the heavens has our sun passed
through? Has it moved in a straight line or in a
closed orbit as do its own satellites?

How far, moreover, has it advanced in its evolu-
tion after pouring forth its rays of light and heat
during this journey at a most extravagant rate
with no sign of diminishing force? Unanswerable
questions as yet. One fact is reasonably certain,
however. No serious catastrophe, such as a col-
lision with or close approach to a neighboring sun
either dark or light, has occurred during this vast
period. Wherever our sun has journeyed it has
been allowed to trace its path undisturbed by out-
side influences.

The life process nas slowly and steadily ad-
vanced upon the earth and possibly upon other
planets of the solar system as well during this pe-
riod. As far as our own planet is concerned, evi-
dence of this undisturbed development is stored
away in geological formations.

Collisions or close approaches of stars are such
167

SPLENDORS OF THE SKY

rare phenomena, occurring so far only in the more
congested regions^ of the Milky Way, that it is
stated as one of the fundamental laws of the uni-
verse that "the stars describe paths under the gen-
eral attraction of the stellar system without inter-
fering with one another. ' '

One of the most interesting and important prob-
lems of modern astrophysics is to determine the
form and extent of the system of stars to which
we belong. A beginning at least has been made
toward the solution of this problem. Material is
being collected continually, day by day and year
by year, bearing upon the number of the stars,
their velocities both in the line of sight and across
the line of sight, their distribution with reference
to the plane of the Milky Way, which is recognized
as the foundation of the system, and their physical
characteristics as well, including relative masses,
densities and luminosities.

One of the most important discoveries in astro-
physics was made through painstaking examina-
tions of the motions of a great number of stars.
It was in 1904 that the noted astrophysicist
Kapteyn first proved in this way the existence of
two intermingling star streams and showed that
168

SPLENDORS OF THE SKY

the motions of the stars were according to law and
order and not at random.

More and more facts are gradually being gath-
ered as to the nature of these two star streams.
It has been established by this time that the great
majority of the stars belong to one or the other
of these two great streams. Also that the number
of stars in the two streams are in the ratio of three
to two and their velocities in the ratio of 1.52 to
0.86; that is, the stars in one stream are more
numerous and move more rapidly than the stars
of the other stream in the above proportions. It
has been found, moreover, that the motion of one
stream relative to the other is parallel to the plane
of the Milky Way, emphasizing the importance of
this formation in the stellar system.

It is a peculiar fact that the Orion or Helium
stars scarcely partake of this star streaming tend-
ency, though they show a decided inclination to
drift in groups, all the members of a group moving
in the same general direction and with the same
speed.

The Pleiades and the chief stars in the constella-
tion Orion are notable among these moving clus-
ters. This gregarious habit is not entirely confined

169

SPLENDORS OF THE SKY

to the Helium stars, for some stars as far advanced
as the sun in evolution show the same trait.

The stars that most closely follow the directions
of the two interpenetrating star streams are the
Hydrogen stars. Their preference for these two
streams is most marked. The older stars, espe-
cially the red stars, show a tendency to diverge
from the directions of the two streams. The aver-
age rate of motion of the red stars of advanced
age is three times as great as the extremely slug-
gish rate of the Orion stars and their independ-
ence of motion is much more marked, for they
show no inclination to remain in or near the plane
of the Milky Way, as do the earlier type stars.

Though the two star streams to which the major-
ity of all the stars belong represent a fundamental
feature of the stellar system, it is believed that
they are but a first approximation to the motions
of the stellar system. The more recent investiga-
tions in astrophysics, especially those connected
with the spiral nebulae and globular star clusters
as external systems of stars, seem to indicate the
possibility of a spiral form for the sidereal system
to which we belong.

Nothing is known that contradicts this belief,
170

SPLENDORS OF THE SKY

while the star streaming characteristic mentioned
above is in line with the theory. It has been sug-
gested by some astronomers that the dense star
clouds of Cygnus or of Sagittarius may be the
strongly condensed centre or nucleus of our stellar
system and that the spiral arms lie along the plane
of the Milky Way. Whether matter is flowing
along the spiral arms toward the nucleus or from
the nucleus outward along the spiral arms, streams
of matter will flow in opposite directions where
the arms merge into the central nucleus.

What would be the nature of stellar movements
in a system possessing a double armed spiral
formation cannot be stated until the dynamics of
motion in spirals is known. At present there is
no clue to the law that governs such motion.

Tf the stellar system is indeed a spiral forma-
tion, more extended study of the relative motions
of the stars will eventually reveal the law that
governs their motion. It might then be possible
to trace the path of our sun through the system of
the stars just as it is now possible to trace the
paths followed by his satellites within the solar
system.

171

CHAPTER XXII

THE MILKY WAY

TO THE people of all ages and nations the Milky
Way or Galaxy has ever been an object of awe
and admiration. Many beautiful though fanciful
stories exist concerning it. It has been called both
the Sky River and the Path of Souls. In Scandi-
navia, where it arches magnificently through the
zenith in winter months, it is the Winter Street,
and another favorite name for it is Jacob's Road.

The true immensity and grandeur of this girdle
of the universe the human mind can hardly grasp.
It is, as it were, the equatorial belt of the sidereal
system and marks the outermost confines of the
universe. The distances of the stars that belong to
it must be measured by the thousands of light
years.

Suns heaped upon suns occur here in such pro-
172

SPLENDORS OF THE SKY

fusion that in certain of the denser portions it is
impossible to form any estimate of their true
number. Nebulae and star clusters as well as stars
surrounded by nebulosity are intermingled with
the dark lanes and stretches of inky blackness. An
example of the latter is the Coal Sack in the South-
ern Cross, not visible in our latitudes. These
darker portions are as characteristic of the Milky
Way as the bright knots and streamers of light
so frequently met with. Many of them are truly
rifts in the star clouds through which we see into
space beyond, but dark nebulous matter is also
abundant in the Galaxy, in fact nebulosity both
light and dark is a strong characteristic of galactic
regions.

Here, too, tend to collect the younger members
of the stellar system, the Wolf-Eayet or bright
line stars, with a type of spectrum bordering upon
that of gaseous nebulas, and the helium stars.
Both groups come early in stellar evolution. The
Wolf-Rayet stars are never found anywhere except
in the Milky Way and in the Greater and Lesser
Magellanic Clouds, two small, somewhat circular
regions in southern circumpolar skies very similar
in nature to the Galaxy. The bluish-white helium

173

SPLENDORS OF THE SKY

stars show a decided preference for the plane of
the Milky Way and so also do the green or gaseous
nebulas and the temporary stars or Novae. With
hardly an exception the latter have flashed out in
the regions of the Milky Way. On the other hand,
the white or spiral nebulae conspicuously avoid
galactic regions and seek the neighborhood of the
galactic poles, particularly in Virgo and Canes
Venatici, in northern latitudes. It is believed by
many astronomers that these spirals are not nebulae
at all but " island universes," as they are called,
lying beyond our stellar universe and so distant
that we cannot distinguish their true stellar na-
ture. There is also the attendant theory that our
own universe is of spiral form with its nucleus in
some galactic region and its spiral arms in the
plane of the Milky Way. If spiral nebulae shall
be found on future investigation to be, in truth,
exterior universes it will be reasonable to assume
by analogy that our universe also has a spiral
form.

Counts of stars in various parts of the heavens
have established the fact that the great majority
of the stars in the universe crowd toward the ga-
lactic plane, and by far the greater number of
174

DARK MARKINGS IN THE MILKY WAY

(Photographed by Barnard on Mt. Wilson with the Bruce telescope)

SPLENDORS OF THE SKY

these are actually within the bounds of the Milky
"Way. There is a noticeable thinning out of stars
as we approach the galactic poles and an increase
in the number of spiral nebulae. This has led to
the belief that the shape of our stellar universe is
decidedly flattened in the direction of the galactic
plane. It has been likened to a disk in shape, the
most distant regions of the Milky Way marking
the confines of our visible universe. It has been
judged that our particular solar system at present
occupies a position well within the Milky Way a
little above the galactic plane and part way from
its centre to its edge, far from the central aggrega-
tions of the Galaxy. This belief is based partly
upon the form of the Milky Way as seen from our
viewpoint. To us it appears as a great circle en-
compassing the heavens.

In northern latitudes the Milky Way is never
seen to run due north and south or east and west,
but crosses the sky diagonally and is best seen in
fall or late summer. In spring it lies too near
the horizon to be well observed. From circum-
polar regions through Cassiopeia to Cepheus and
into Cygnus it runs. Here it divides into two
parallel branches for nearly one-third of its entire

175

SPLENDORS OF THE SKY

length, running through Aquila, Ophiuchus and
Sagittarius to Scorpio. There the two branches
join once more and it passes beyond our vision into
southern skies, where it enters Centaurus and Crux,
the Southern Cross, and traverses the magnificent
and extensive constellation of Argo Navis, which
contains Canopus, the second brightest star in the
heavens. From Argo Navis it curves northward
once more, passing close by Canis Major, which
contains Sirius, the brightest of the stars, and
running through Monoceros, where it is extremely
brilliant, to Gemini and Taurus, then through
Auriga and Perseus to circumpolar regions in the
neighborhood of Cassiopeia once more. Through-
out this entire course it exhibits a wonderful diver-
sity of form and structure. We note that it in-
cludes in its midst or passes near many of the
brightest of the stars, while it includes an over-
whelming majority of the fainter stars. The
brilliancy of the Milky Way and its immediate
neighborhood is in striking contrast to the dearth
of stars near its poles.

Since the stellar system is undoubtedly condensed
toward the plane of the Milky Way and we are
situated between the centre and the edge of this
176

SPLENDORS OF THE SKY

plane, it is evident that we look through a dense
layer or stratum of stars in the direction of the
Milky Way. All the stars that lie in the direction
of the Galaxy do not belong in its midst, but are at
varying distances from us. The true aggregations
of the Galaxy are at excessive distances and are
for this reason extremely faint, on the average
between the fourteenth and sixteenth magnitude,
and probably only in a few rare cases brighter
than the eighth magnitude. As distinct points of
light they are beyond the reach of the unaided eye
and give us only the impression of hazy light.

Successful attempts have been made to portray
various regions in the Milky Way, especially in
Sagittarius and Cygnus, and we cannot fail to be
impressed with the impossibility of making any
estimate of the number of suns represented in some
of these views. Such, moreover, is the diversity
of form of its various parts that it has been said
no one region can be regarded as typical of the
entire Milky Way. The stupendous scale of this
wonderful structure fills us with awe. Suns are
here crowded together until they seem as countless
as the grains of sand upon the seashore, and yet
there is no doubt that they include among their
177

SPLENDORS OF THE SKY

number some of the giants of the universe only
dimmed to our eyes by immeasurable distances.

We cannot fail to recognize the fact that there
is some definite plan or purpose in this structure
in its relation to the remaining portions of our
universe. It is not unmeaning chaos that we look
upon, for certain types of stars crowd toward the
Galaxy while others avoid it, and certain physical
characteristics are shared by all of its members.

We can only stand awestruck before the plan
of the universe that our minds cannot grasp or
comprehend.

178

CHAPTER XXIII

DO DARK STARS EXIST IN THE HEAVENS?

DARK stars abound throughout the universe
either in a solitary state or associated with
brilliant companions. Though invisible, they have
disclosed their presence to us in a variety of ways.
It may never be possible to form any estimate of
their true numbers, but we cannot doubt their
existence.

Many a dark or feebly luminous body of sun-
like dimensions has been detected by the perturbed
motion of some bright star with which it is phys-
ically connected. Sirius and Procyon were ob-
served to describe little ellipses under the influence
of some unseen force long before their companions
were discovered. The companion of Sirius, though
not absolutely dark, is one of the most feebly lumi-
nous bodies known. Its mass, however, is nearly

179

SPLENDORS OF THE SKY

one-half that of Sirius and it has a powerful
attractive force.

It is now conservatively estimated that one star
in every three is either double or multiple ; that is,
belongs to a system of two or more stars in revo-
lution around a common centre of gravity, and
in numberless cases dark stars are included in
these systems. Sometimes the components of these
systems are so close that in the most powerful
telescopes they appear as a single star, but their
composite nature is revealed by the spectroscope,
which shows a doubling or shifting of the lines
of the spectrum. These are called spectroscopic
binary systems. The doubling of the spectral
lines shows a second luminous body to be present,
but the shifting of the lines without doubling
shows that the bright star has a companion giving
little or no light. As the bright body recedes in
its orbit under the sway of its dark attendant the
lines shift toward the red end of the spectrum,
and as it turns in its orbit so as to approach the
earth the lines shift toward the violet end of its
spectrum, and the amount of the shift shows the
velocity with which it moves in its orbit. In some
cases it is possible to determine not only the time
180

SPLENDORS OF THE SKY

it takes for the star to describe its orbit and the
velocity with which it is moving, but also the dis-
tance between the two components in miles, their
relative mass and brightness, and their mass and
brightness as compared with that of our own sun.
All this is possible, however, only in case the dis-
tance of the system from the solar system is known.

Stars are often variable in light due to periodical
eclipse by dusky satellites. Such is Algol, the
Demon Star, whose wink every three days means
that a dark body passes before his face and shuts
off fully five-sixths of his light. Stars that are
regularly occulted or eclipsed by dark attendants
form a large class of stars known as eclipsing
variables. They furnish another proof of the ex-
istence of dark bodies.

It is of peculiar interest that dark stars are
often associated with stars known to be young;
that is, with Helium or Sirian stars. Since mem-
bers of double star systems have presumably at
one time formed a single mass, gradually separat-
ing into two or more components and drawing
further and further apart as time goes on, we
would expect the components to show signs of
equal age. "Why should they be in so many cases
181

SPLENDORS OF THE SKY

of nearly equal mass, but widely different light
giving power? We must conclude that there are
two classes of dark stars, those dark through old
age coming at the end of the evolutionary stage,
and those dark because they are imperfect ra-
diators and have not the necessary physical prop-
erties for keeping up long continued radiation
without appreciable loss of light and heat. Pos-
sibly at the time of their separation from the orig-
inal mass there was unequal distribution of the
materials possessing the light and heat giving prop-
erties needed for long continued radiation. We
can only conjecture as to the cause, but the fact
remains that intensely brilliant stars with every
sign of youth are physically connected with stars
necessarily of equal age but emitting no appre-
ciable light. Such well known bright stars as
Sirius, Spica, Procyon and Castor are attended
by faint or invisible companions.

Whether there exist in space systems in which
all the members are dark we have no means of
knowing, but we can reasonably assume that as old
age overtakes the brighter members of these systems
they too will become dark. The systems of 61
Cygni, one of our nearer neighbors, includes one
182

SPLENDORS OF THE SKY

or more invisible members, and the entire system
shows signs of great age. There seems no escape
from the conclusion that in far distant ages the
entire system will be devoid of light. Investiga-
tions are also establishing the fact that the velocity
through space of stars and star systems increases
with age. If so, with what tremendous velocity
extinct stars must be rushing on their mysterious
journeys to unknown fates!

We have been considering so far dark stars that
are associated with bright companions. The sud-
den blazing forth of temporary stars has led to
the belief that dark stars occur in an isolated state
as well. It is only when collisions between dark
stars occur or when dark bodies pass through
resisting nebulous matter with the attendant burst-
ing forth of light that we can know of their exist-
ence.

Our own sun in his old age would be a star of
this class. For the ruler of our solar system is
supreme and shares his glory with no other body
of sunlike dimensions. Our own system may be
but one of many that have dark attendant satellites
vastly inferior in mass to the ruling body around
which they circulate. And when old age falls upon

183

SPLENDORS OF THE SKY

the ruler of such a system and his light and heat
have disappeared he has no choice but to join
the host of dark stars, as cold and inert as his
lifeless attendants that still circle ceaselessly
around their ruler as he journeys onward to ex-
tinction. We can only reason about the existence
of such dark and lifeless systems through analogy.
We see in the heavens the nebulae that give birth
to stars. We see also young stars, and stars in
the zenith of their splendor, such as our own sun,
and again stars failing in light and heat with
advancing old age; and why not cold, rayless
stars?

It is known that stars exist in a non-luminous
condition in mixed systems of light and dark stars.
The telescope and spectroscope prove this to us.
So it is reasonable to assume that dark bodies exist
among the single stars.

Dark bodies of planetary size attendant upon
bright stars could never be detected by any means
at our disposal, for bodies shining only by reflected
light from a central sun and of such minute pro-
portions compared with their luminary would be
hopelessly lost in his rays. It is only when a
satellite has sunlike dimensions that it can influ-
184

SPLENDORS OF THE SKY

ence the ruler of the system and reveal its pres-
ence by the perturbations it produces. If our most
powerful telescopes were placed at the distance of
Alpha Centauri, the nearest star, and pointed at
our solar system, it would never disclose the fact
that our sun had a single attendant planet.

It is doubtful if we can ever fulfil our very
natural desire to know whether other stars are
attended by worlds of planetary size.

As regards dark suns, however, Bessel, one of
the greatest of mathematicians, said we had reason
to believe there may be as many dark stars as
bright ones.

185

CHAPTER XXIV

THE BRILLIANT NOVA OF 1918, NOVA AQUILJE NO. 3

SHORTLY after the moon's shadow had swept
across the United States on the 8th of June,
1918, and while, in fact, members of many success-
ful eclipse expeditions were busily engaged in de-
veloping plates and packing up eclipse apparatus,
there suddenly appeared in the heavens, in the
constellation Aquila, the Eagle, the most brilliant
temporary star or nova that has been seen since
Kepler 's star suddenly flashed into view in 1604,
more than three hundred years ago.

According to a Harvard College Observatory
bulletin numerous telegrams were received at the
Harvard Observatory during the night of June 8
from all parts of the United States and Europe
announcing the independent discovery of the nova
by many amateur and professional astronomers.
186

SPLENDORS OF THE SKY

The first person to report the discovery was Mr.
W. H. Cudworth, who sent a telephone message
from Norwood, Mass. Due to differences in longi-
tude the star was probably first seen in Europe.
Harvard observers immediately proceeded to photo-
graph the visitor and look up its past history.

Photographic plates dating back as far as May
22, 1888, showed a faint star of the eleventh mag-
nitude whose position in the heavens was identical
with that of the nova. Several hundred plates
were examined at the Harvard Observatory in
order to trace the light variations of this star in
the past thirty years. There appear to have been
slight fluctuations in the brightness of the star
during that period that have a range of about
half a magnitude.

The following facts were established from
examination of photographs. On June 3 this
wonderful star possessed its normal brightness for
the past thirty years, that of a faint star of the
eleventh magnitude. Because of clouds no plates
were exposed on June 4, 5 and 6. On June 7 the
star appeared as a sixth magnitude star just at the
limit of visibility to the unaided eye. Its bright-
ness had therefore increased one hundred fold in

187

SPLENDORS OF THE SKY

less than four days. On June 8, the memorable
day of its discovery, it had become a star of the
0.5 magnitude and was a magnificent blue-white
star nearly as bright as Vega, shining all the more
resplendently since it appeared in a part of the
heavens where few first magnitude stars appear.

Upon June 9 Nova Aquilae No. 3, as it has been
labelled astronomically, attained what appears now
to have been its maximum brightness, when it
outshone the famous Nova Persei of 1901 and prac-
tically equalled Sirius in brilliancy. According to
observations of Prof. E. E. Barnard, made June 9,
its magnitude was minus 1.4, while the magnitude
of Sirius is given as minus 1.6.

How long it will remain visible to the naked eye
is doubtful. Nova Persei faded from view within
a month and was conspicuous for only a few days.
It was unlike the present nova in being distinctly
ruddy at maximum brightness. It is customary
for temporary stars to fade rapidly but fitfully
away. Kepler's star, which was nearly as bright
as Venus at maximum brightness, was unusual
among temporary stars in remaining visible for
fully two years.

The nova is situated in one of the two branches
188

SPLENDORS OF THE SKY

of the Milky Way, that lie between Aquila and
Scorpio, and it was all the more conspicuous for
appearing in a portion of the heavens where few
bright stars are seen.

On June 8 the spectrum of the nova was found
to be that of an early type star, with dark lines
due to absorption of the light of the stellar core
by cooler hydrogen gas surrounding the star. A
spectrum taken at Harvard on June 9 confirmed
the first observation and showed narrow, dark
hydrogen lines on a nearly continuous background.

All astronomers agree that the sudden outburst
of novae, a rare phenomenon, is evidence of some
sort of a celestial catastrophe, but the exact cause
of the sudden and tremendous increase in the light
giving powers of the star is still in doubt. The
latest theory assumes that a dark or light star
encounters a stream of nebulous matter, and its
heat and light are enormously increased by the
friction created by its passage through the nebula.
Considerable weight is given to this theory by the
fact that Nova Persei was observed to be sur-
rounded by nebulous matter soon after its sudden
appearance. Nebular conditions still exist around
this star, which is still visible in large telescopes.

189

SPLENDORS OF THE SKY

At first it was thought that matter was travelling
outward from the star with the velocity of thou-
sands of miles per second, but this appeared most
unlikely, and it was finally shown that the phe-
nomenon could be explained by assuming that the
surrounding nebula was illuminated by the waves
of light proceeding outward from the star. Light
was being reflected to us from the dark nebula
just as the planets and moon reflect the light of
the sun. The theory of the origin of novae by
encounters between stars and nebulous matter does
not satisfactorily explain all that has been observed
in connection with the appearance of these stars,
and the origin of novas is still a subject open to
discussion.

The novae show no measurable parallax and
therefore their distance is unknown, but it is as-
sumed to be very great, certainly not less than
300 light years, possibly in some instances, several
thousand light years.

The great value of preserving photographic
records of the heavens appears in connection with
the discovery of this star. It is possible to prove
by reference to the photographs of this portion
of the sky taken at the Harvard College Observa-
190

SPLENDORS OF THE SKY

tory that the present nova was not a dark star
previous to its present outburst, but a faint star
of the eleventh magnitude, and all its past history
for thirty years is now available. The sudden rise
of this star to the minus one and four-tenths mag-
nitude represents an increase in light giving power
of about ninety thousand fold. In other words,
when this star attained its greatest brilliancy on
June 9 it would have taken the combined light of
90,000 stars of its former brightness to equal it.

Since Nova Aquilae has no measurable parallax
it must have been before its outburst at least equal
in brightness to our own sun. At the time of its
outburst its light was therefore equal to the light
of many thousand such suns as our own. It is
possible that Nova Aquila& is situated in distant
regions of the Milky Way where lie vast nebulous
tracts of matter, and that even before its outburst
it was superior to our own sun in brilliancy.

Possibly at the time of its outburst a catastrophe
became visible that took place several thousand
years ago, for if the star is several thousand light
years distant the light that now reaches us started
on its journey many centuries ago.

Since the date of its discovery astronomers have
191

SPLENDORS OF THE SKY

obtained many spectroscopic records of the changes
that have taken place in this brilliant nova. Fol-
lowing the usual course of temporary stars Nova
Aquilae No. 3 decreased fitfully but rapidly in
brightness and in a few months became a faint
fifth magnitude star, just perceptible to the naked
eye.

192

CHAPTER XXV

CALCIUM GAS IN THE MILKY WAY

NOVA AQUIL^J No. 3, the brilliant temporary
star that suddenly burst forth June 8, 1918,
and then rapidly decreased in brightness until it is
now scarcely visible to the eye, has been under
continual observation by astronomers since the date
of its first appearance.

A most unusual and unexpected result of the
spectroscopic study of this star has been the de-
tection of clouds of calcium vapor lying in the
Milky Way between us and the new star.

This discovery has been announced in a com-
munication to the Observatory, a British publica-
tion, by the prominent British astronomer Ever-
shed, stationed at Hodaikanal, India, who reports
the existence of fine dark lines of calcium in the
spectrum of the nova in a normal position. Since

193

SPLENDORS OF THE SKY

all the spectral lines of a nova are always greatly
displaced and distorted, due to the abnormal con-
ditions existing in such stars, the presence of the
lines of any element in a normal position points
to an origin of these lines external to the scene
of the outburst.

According to one of the first laws of spectrum
analysis, upon which depends our knowledge of
the physical condition of the stars, if light from
a certain source, such as an incandescent solid,
or liquid, or gas, under extremely high pressure
(in this case the nova), passes through a cooler
intervening gas, the latter will absorb from the
source of light beyond the particular elements
of which the cooler gas consists and as a result
the spectrum of the hotter body (the nova) will
be crossed by dark absorption lines of the cooler
intervening gas.

It is upon this same principle that the elements
that enter into the composition of the cooler en-
veloping gases of a stellar body can be determined.
Upon the continuous band of color emanating
from the star's interior appear the dark absorp-
tion lines originating in the cooler atmosphere of
the star.

194

SPLENDORS OF THE SKY

Were the outer gaseous envelope of Nova
Aquilse in a normal condition of temperature and
pressure its absorption lines would be in their
normal position in the spectrum, and the existence
of these clouds of calcium vapor lying in the Milky
Way between us and the nova would not have
been suspected, since in that case the lines of
calcium in the star's atmosphere and in the ex-
terior clouds of calcium would have been coincident
and would have been attributed entirely to a stellar
origin. In the atmosphere of a nova, however,
conditions are far from normal.

A celestial catastrophe has occurred and ab-
normal conditions of temperature and pressure
existing in the star's outer gaseous envelope are
registered in the form of distorted and displaced
lines and bands both bright and dark in the star's
spectrum. Only the lines of calcium vapor far
exterior to the scene of the catastrophe remain
uninfluenced by these conditions and appear fine
and dark with the distorted, abnormal spectrum
of the nova for a background. Remove the nova,
or place in its stead a normal star, and the pres-
ence of the calcium clouds would remain unknown.

Continuing his investigation of the calcium lines
195

SPLENDORS OF THE SKY

in Nova Aquilse and looking up the records of
past novae and a number of binary stars, which
also show displaced lines due to the mutual revo-
lution of the components of each system, Evershed
made some additional discoveries of great interest.
Observations had been recorded in the past of the
existence of the dark absorption lines of calcium
in the spectrum of Nova Persei, which appeared
in 1901 and closely rivalled Nova Aquilae in
splendor.

The lines of calcium also appeared in their nor-
mal position in this nova, though all the other
lines of its spectrum were displaced. A few binary
stars also showed the calcium lines in a normal
position, though all lines originating in the atmos-
phere of these stars were displaced owing to
mutual revolution of the components of these star
systems which produces periodic displacements of
all their spectral lines. Evershed concluded as a
result of his observations of all these stars, ten
or twelve in number scattered over widely sepa-
rated regions, that there exists in the Milky Way
vast clouds of calcium vapor through which the
light of these stars passes before it reaches our
eyes, and he also concluded as a result of further
196

SPLENDORS OF THE SKY

investigations that these clonds lie virtually sta-
tionary in space. So immovable do they appear
that he considers they would furnish a valuable
method for a new determination of the motion of
our own sun through space.

It has long been known that vast clouds of
nebulous matter exist in the Milky Way, but this
is the first time that the presence of a gaseous
tract of matter has been detected by absorption
lines produced in the spectrum of a star far
exterior. It is a most unique and unusual dis-
covery, and shows what valuable and unexpected
results may be obtained from spectroscopic observa-
tions of the stars. Under ordinary circumstances,
the existence of these vast clouds of calcium vapor
would be unknown and unsuspected.

A normal stellar spectrum would not reveal
their presence. Yet the rays of light from Nova
Aquilse and Nova Persei, as well as certain binary
star systems, have not only told the secret of the
physical condition of these stars but have also
brought us the proof of encounters with interven-
ing gases on their long journey through space to
the solar system and our own planet.

An interesting and valuable field for future
197

SPLENDORS OF THE SKY

study has thus been indicated. Observations of
other stars with displaced spectral lines may
enable astronomers to detect the presence of clouds
of gas lying between us and such stars and to
determine in addition whether these clouds of
vapor are at rest or drifting through space.

Why calcium vapor should exist in such pro-
fusion in space is a mystery. As is well known to
astronomers, there is a certain type of stars known
as calcium stars, whose spectra are characterized
by the presence of strong absorption lines of cal-
cium, indicating that calcium vapor occurs in great
abundance in the atmosphere of such stars. To
this class of stars belongs Canopus, one of the
greatest suns of the universe, and Procyon, a near
neighbor of the solar system, which is about ten
times more luminous than the sun.

In addition to dominating the spectra of stars
of this class calcium is found in great quantities
in the solar type stars, to which our own sun be-
longs, and less conspicuously in later type stars.
It is only in the helium and hydrogen stars that
this element appears to be absent. The distribu-
tion of this element in the atmosphere of the sun
can be studied by means of the spectro-heliograph,
198

SPLENDORS OF THE SKY

which makes it possible to photograph the sun in
the light of a single spectral line.

The circulation of calcium vapor in the sun's
atmosphere has been extensively studied by this
method, and it has been noted as a singular and
puzzling fact by astronomers interested in solar
research that the vapors of this comparatively
heavy element are frequently found at very high
levels in the sun's atmosphere.

It is, moreover, a noteworthy fact that this ele-
Jnent, which apparently occurs in the greatest
abundance in stars of many types, and, as is now
known, exists in different portions of the universe
in the form of vast clouds, is also of the greatest
importance upon our own planet, earth.

It is this element that enters into the structure
of the bones and is so essential to virtually all
forms of animal life. Though its particular impor-
tance in the fashioning of the stars and in the
universe as a whole is unknown, it is certain that
without it animal life as it now exists on our
planet would be impossible.

199

CHAPTER XXVI

THE SPIRAL NEBULAE AND THE GREAT NEBULA IN
ANDROMEDA

^TT^HE discovery in recent years of a number of
-•• novae, or temporary stars, in spiral nebulas is
regarded by astronomers as a matter of unusual
importance since it may have a direct bearing
upon the baffling problem of the nature, size and
distance of these peculiar spiral formations now
known to exist in the heavens in numbers running
into the hundreds of thousands, if not millions.

It would in no wise lessen our interest in the
most famous of all spirals, the Great Andromeda
Nebula, to discover that it is an " island universe"
consisting of millions of suns as well as vast nebu-
lous formations and star clusters similar to those
found in the Milky Way of our own system.

According to astronomers who have made a spe-
200

SPLENDORS OF THE SKY

cial study of these spiral formations, dimensions
and distances of a higher order than that of the
stars are to be expected for the spiral .nebulae if
they are remote universes

The marked distribution of all stars, star clus-
ters and gaseous nebulas within our own universe
with reference to the Milky Way, or Galaxy, has
long been known. In or near this plane are to be
found the majority of all stars, bright as well as
faint — though the condensation is more marked
for faint stars — showing that our system is de-
cidedly flattened toward the plane of the Galaxy.
The tendency of the gaseous nebulae and the plan-
etary nebulae, as well as the vast star clouds and
tracts of irregular nebulous formations, dark as
well as light, to adhere closely to the neighbor-
hood of the Galaxy is well known.

In marked contrast to this we find that the spiral
nebulae actually avoid the regions of the Milky
Way and are found in greatest abundance in parts
of the heavens farthest removed from galactic re-
gions; and, what is of special interest in this con-
nection, all temporary stars discovered up to the
present time, about thirty in number, have been
closely confined to the Milky Way, with but three
201

SPLENDORS OF THE SKY

exceptions. One of these, T Coronae, was not a
typical nova. The other two were found in spiral
nebulae and were the only temporary stars known
to exist in spirals until quite recently, when Prof.
Kitchey at Mount Wilson discovered a nova in the
spiral nebula N. G. C. 6946.

The discovery of this nova, the third to be
found in a spiral, caused a suspicion that there
might be an actual physical connection between
the spiral formation and the star. The probability
that three temporary stars should chance to be in
line with spiral nebulae was very small. The dis-
covery of this nova led to a reexamination of
former photographs of spiral nebulae with the
result that eleven temporary stars were found
in spiral nebulae as against twenty-six previ-
ously found in the Milky "Way. Throughout the
remainder of the heavens temporary stars are non-
existent.

Another extremely important point brought out
by astronomers in connection with the discovery
of these temporary stars in spirals is the great
difference in the brightness of the novae in spirals
and the novae in the Milky Way. Temporary stars
that have appeared in the Milky Way have usually
202

THE GREAT SPIRAL NEBULA IN ANDROMEDA

(Photographed by Ritchey with the 2-ft. reflector of the Yerkes Observatory)

SPLENDORS OF THE SKY

teen somewhat sensational objects, in some cases
appearing at their maximum fully as brilliant as
the brightest of the stars or even the planets
Jupiter or Venus. The novae in spiral nebulas, on
the contrary, are excessively faint objects, averag-
ing about the fifteenth magnitude, entirely invisible
at their maximum brightness except in the most
powerful telescopes.

Between the average brightness of the temporary
slars appearing in the Milky Way and those de-
tected in spirals there is a difference of fully ten
magnitudes. If we assume that the two classes of
novae are about the same in actual luminosity this
great difference in apparent brightness is due to
differences in distance. A difference of ten mag-
nitudes in apparent brightness of two stars that
are in reality of equal light giving power means
that the fainter star is one hundred times more
distant than the brighter. We have no knowledge
of the actual distance from us of the temporary
stars situated in or near the Milky Way, but it is
believed to be very great, probably in many cases
as high as several thousand light years. This
would place the spirals at distances to be measured
by hundreds of thousands of light years and give

SPLENDORS OF THE SKY

support to the theory that they are "island uni-
verses " of millions of suns.

Even with the sixty-inch reflector of the Mount
Wilson Observatory no star in the heavens fainter
than the twentieth magnitude can be detected.
Photographs of spirals taken with this instrument
?$how no individual stars, but nebulous, starlike
condensations analogous probably to the nebulous
star clouds of our own Galaxy, its star clusters
and its nebulous formations. The appearance of
a temporary star of the fifteenth magnitude in a
spiral nebula would therefore mean the appear-
ance of a star that is at least several hundred
times brighter than the brightest individual star
in the nebula, while the nova of 1885 in the Great
Andromeda Nebula, which was of the seventh mag-
nitude at maximum and therefore almost visible
to the naked eye, must have attained an actual
luminosity hardly to be equaled by the combined
light of a million of the brightest stars in the
heavens.

Dr. Shapley has pointed out that this unusual

case would have a parallel in our own Galaxy,

however, if we make the assumption that Nova

Persei, the famous temporary star of 1901, is situ-

204

SPLENDORS OF THE SKY

ated in some one of our most distant galactic clouds.
The noted temporary stars of Hipparchus and
Tycho Brahe may have originated in far distant
galactic regions for all we know to the contrary.
If so they burst forth with a temporary splendor
equal to several million such suns as our own.

Though the question of the true nature of spiral
nebulae is still an open one, the appearance of
extremely faint novae in their midst must be con-
ceded to be a strong argument in favor of the view
that they are far distant external universes of the
order of magnitude of our own stellar system and
of the attendant theory that our own universe,
composed of some hundreds of millions of stars
and nebulous formations, luminous as well as non-
luminous, has a spiral formation with the double
branching spiral arms to be traced among the
star clouds of the Galaxy. Upon the assumption
that the spirals are far distant universes, the fact
that they so conspicuously avoid galactic regions in
strong contradistinction to nearly all other classes
of objects in the heavens is explainable. If they
are situated at distances more remote than other
celestial objects the vast tracts of nebulous matter,
dark and light, in galactic regions and the dense
205

SPLENDORS OF THE SKY

star clouds that abound in this plane would hide
from view spirals lying near the Milky Way.

Were our own system of stars as far away as
the Great Nebula in Andromeda it would appear
very much as the Great Nebula in Andromeda
does to us. Without telescopic aid it would be
seen as a faint patch of light about the size of the
full moon. When viewed with the most powerful
telescopes its most brilliant individual stars would
still remain hopelessly invisible, but various nebu-
lous condensations of light would appear, suggest-
ing conglomerations of many stars and nebulae.
Our own little sun at this distance would be
beyond the range of all telescopes. There would
be little reason to suspect we were viewing a uni-
verse of hundreds of millions of suns or that all
these suns were in unceasing motion in obedience
to the mysterious laws governing their formation
and that of the universe to which they belong.

Since the Andromeda Nebula is exceptionally
large, it is either comparatively near or an unusu-
ally large formation. Many of the spiral nebulae
are extremely faint. They appear in the greatest
abundance in the heavens. Of the fainter nebulae
virtually nothing is known. The thought that these
206

SPLENDORS OF THE SKY

faint spirals may be aggregations of suns at dis-
tances to be measured by hundreds of thousands
of light years is staggering to the imagination of
man.

207

CHAPTER XXVII

GASEOUS NEBULJE AND THE ORIGIN OF THE STARS

^TT^HE gaseous or green nebula*, so named from
•"* the greenish tinge imparted to them by the
presence of the unknown gas nebulium, present
problems to the astronomer as interesting and im-
portant as those connected with the noted spiral
nebulae. These two types of nebulas are radically
different in their composition and in their distri-
bution in the heavens.

Gaseous nebulas are beyond a doubt members of
our own system of stars. They crowd densely
toward the Milky Way, the groundwork of our
universe. The spirals as conspicuously avoid it.
The latter, it is suspected, may be systems of
stars independent of and external to our own.
The gaseous nebulas we think of as the material
from which the stars are fashioned.
208

SPLENDORS OF THE SKY

Their extent is enormous. We have as yet no
definite idea of their distance, but it must be as
great as that of the nearer stars. Most probably
they occur in greatest profusion among the more
dense star clouds of the Milky Way at distances
to be measured by thousands of light years. In
many cases they must occupy an interval of space
so great that light would require many years to
cross it.

Vast gaseous nebulae enwrap, in some instances,
moving clusters composed of many stars such as
the Pleiades and the stars of Orion. The Great
Orion nebula is the finest of all the gaseous nebulas.
Double, triple and multiple stars are enmeshed in
its extensive folds.

The extreme tenuity of the gaseous nebulae is
as astonishing as their vast extent. One ten thou-
sand millionth of the density of our own atmos-
phere at standard pressure is one of the estimates
of the density of the denser portions of the Great
Nebula in Orion.

It is difficult to imagine the condition of matter

in such an extreme state of rarefaction. Yet these

nebulae assume an infinite variety of form and

structure. In addition to the vast nebulae of

209

SPLENDORS OF THE SKY

irregular form there are the ring or annular nebulae,
peculiar formations probably spheroidal in form,
with a star of variable luster often shining with-
in the ring. There are the Saturn nebula,
the Owl, Crab, Dumb-bell, North America and
many other odd shaped gaseous nebulae frequently
named from their fancied resemblance to objects
familiar to terrestrial inhabitants.

There are also the planetary nebulae, a species
of gaseous nebulae named from their resemblance
to faint planetary disks, that are receiving consid-
erable attention at the present time. Astronomers
find their extremely high velocities of motion in
the line of sight which average twenty-four miles
a second surprising and extremely puzzling.

In the scheme of stellar evolution the first type
stars, on the border between nebulous and stellar
conditions, are supposed to follow the planetary
nebulas in order of development, but the very high
velocity of the planetary nebulae would hardly
connect them with the slowly moving new stars.
It has been found that the stars move more rapidly
with increasing age and we should therefore have
to place the planetary nebulae at the end of the
evolutionary chain instead of the beginning, if we
210

SPLENDORS OF THE SKY

<t

consider simply the very high, speed with whloii
they are moving through space.

Some recent investigations of these same planet-
ary nebulae show that they are rotating as well and
that in two special cases the periods of rotation
lie between 600 and 14,000 years and the masses
of the rotating nebulae between three and 100 times
that of the sun.

The planetary nebulae are usually strongly con-
densed toward their centres. Here are found the
denser helium and nebulium gases, while hydro-
gen .occurs chiefly near the outlying portions.

These three gases, hydrogen, helium and nebu-
lium, are the elements always to be found in the
gaseous nebulae, whether irregular or planetary.
They enter into the composition of all nebulae ex-
cept the spirals, which shine on the other hand
with " white " light and give the continuous spec-
trum of incandescent solids or liquids or gases
under high pressure. They are for this reason
often referred to as the white nebulae, as opposed
to the green or gaseous nebulae. The latter show
the typical nebular spectrum consisting of bright
lines of the three gases mentioned.

A bright line spectrum indicates that the source
211

SPLENDORS OF THE SKY

of the illumination is gaseous matter at low pres-
sure. The green nebulas are very feebly luminous
and the nature of their luminosity is one of their
most puzzling features. According to a recent
theory the mysterious element nebulium is some
familiar element electrically excited. Some
astronomers believe that the luminosity of the
gaseous nebulae is chiefly due to electrical excite-
ment of certain portions. In all these nebulas
occur dark portions as well as light. The illumi-
nation is locally condensed and certain portions
seem for some inexplicable reason to have lost their
illuminative power. This would hardly be ex-
pected if the luminosity of the gaseous nebulas
were due to light of incandescence alone. A more
uniform distribution of light would be expected.
It is generally believed that the temperature of
the gaseous nebulas is extremely low and if due
to electrical discharges their average temperature
might approximate to absolute zero.

Tremendous extent, extremely low density and
marked feebleness of light are the three peculiar
characteristics of the gaseous nebulas.

Evidently plan and purpose control the nebulas
as well as the stars. They do not represent mean-
212

SPLENDORS OF THE SKY

ingless chaos, but form one of the links in the chain
of evolution.

It is not by chance that stars, both single and
multiple, are found in the midst of the vast irreg-
ular nebulae, while even the small planetary
nebulae, the annular nebulae and the nondescript
nebulae have in nearly all instances stars closely
associated with them.

It has been pointed out by some astronomers
who are inclined to question the transformation
from nebulae to stars that the nebulosity connected
with these stars may rather result from gradual
change of stars into nebulae, and that the nebu-
losity surrounding the Pleiades and the stars of
Orion are rather emanations of gaseous matter
from these stars and that eventually they will all
be dissipated into nebular form. It has been
pointed out also in this connection that flames of
hydrogen and helium often burst forth from the
solar surface at the rate of 200 miles per second
even under present conditions, while a velocity of
ejection of 380 miles per second would permit
them to leave the surface of the sun never to
return.

The nebulous matter now to be found surround-
213

SPLENDORS OF THE SKY

ing the famous temporary star, Nova Persei, is
instanced in support of the view that stars may be
dissipated gradually or suddenly into a nebulous
state.

Although the existence of dark nebulae closely
resembling the luminous variety in form seems to
show that some nebula at least may become extinct
without passing through the usually accepted or-
der of evolution from nebulae to star, the theory
that gaseous nebulae do not condense into stars
would leave the question of the origin of stars en-
tirely unsettled. That there is a continual cycle
of change from nebulae to star and possibly also
from star back to nebulae by chance encounter of
one star with another or close approach of two
stars seems more in accord with observed condi-
tions. The passage of a star through a stream of
dark nebulous matter would doubtless result in
such nebular conditions as are observed in the case
of the temporary stars, Nova Persei, Nova Aquilse
and others.

Man is handicapped in his observations of the

nebulae by the fact that changes in the form and

structure of these objects are so extremely slow.

A hundred or a thousand years is but a moment iu

214

SPLENDORS OF THE SKY

the life of a nebula. It is, therefore, next to im-
possible to detect a progressive change in any one
nebula that would show whether condensation or
expansion is taking place.

The spectroscope has furnished much valuable
information concerning the gaseous nebulae. In
fact, practically all we know about these objects
has been obtained with the aid of the spectroscope.
We trust also that it will eventually solve the mys-
tery of the strange gas nebulium that is the most
characteristic element of the gaseous nebulae. The
fact that it is unknown elsewhere but adds to the
mystery. The condensation of the gaseous nebulas
into stars and the final transformation of stars
back to nebulae through chance encounters and col-
lisions pictures a state of universal and continual
change, a universe without beginning or end, and
in absence of proof to the contrary this is generally
believed to be the true cycle of change that is tak-
ing place among the stars.

215

CHAPTER XXVIII

THE GREAT STAR CLUSTER IN HERCULES

\ N extensive study of the great star cluster in
<* *• Hercules, in connection with other globular
star clusters, has been made at the Mount Wilson
observatory and results seem to indicate that the
parallax of this noted cluster is less thain one-ten-
thousandth of a second of arc, and that it is at a
distance of 37,000 light years, with a diameter of
several hundred light years.

This faint wisp of light, barely visible to the un-
aided eye on clear, dark, summer nights, thus takes
on the dimensions of a sidereal universe sepa-
rated from us by immensities of space so vast that
our minds utterly fail to grasp them. Thirty-
seven thousand years ago then, if the above esti-
mates are correct, the light that now comes to us
from this gorgeous assemblage of suns started forth
216

SPLENDORS OF THE SKY

on its journey at the rate of 186,000 miles a sec-
ond, and if the cluster were suddenly blotted out
of existence another 37,000 years would elapse
before our solar system would fail to receive its
light.

Only the mos* powerful telescopes are capable
of completely resolving the Hercules cluster into
its stellar components. Of more than 5,000 stars
counted upon one photograph fully 4,000 were
fainter than the thirteen and one-half magnitude
and, therefore, invisible as separate stars in small
telescopes. Long photographic exposures made
with the largest reflecting telescopes bring out
great numbers of extremely faint stars in this clus-
ter lying near the limit of visibility of these great
instruments.

When we consider that the entire space covered
by the Hercules cluster is only about one-sixteenth
of the area of the full moon, it seems almost in-
conceivable that this insignificant little patch of
light represents a mighty assemblage of suns.

A peculiar distribution of stars has been noted

in the Hercules cluster. The brighter stars extend

outward from the centre in curved lines, while the

extremely faint stars show a uniformly globular

217

SPLENDORS OF THE SKY

distribution. Three dark lanes making an equian-
gular juncture near the centre of the cluster were
detected many years ago and later photographs
show a similar formation repeated at other points,
which implies the existence of some definite law of
formation.

The Hercules cluster is considered the finest
globular cluster in the northern heavens, though it
is surpassed in splendor by two clusters in the
southern hemisphere in the constellations Centau-
rus and Tucana. Over 6,000 stars have been
counted in the Centaurus cluster within a space
about as large as that filled by the full moon, and
they average about twelve and one-half magnitude,
a magnitude brighter than those in the Hercules
cluster. In this cluster, also, many extremely faint
stars are present. The globular cluster in Tucana
is somewhat smaller than the Centaurus cluster and
contains about 2,000 bright members that are, how-
ever, more closely crowded together than are the
members of the cluster in Centaurus. The globu-
lar cluster in Tucana, which is a constellation near
the South Pole, is regarded by some as the finest
object in the heavens. The dark lanes noticeable
in the Hercules cluster are entirely absent in the
218

SPLENDORS OF THE SKY

two southern clusters, which, show a decided cen-
tral crowding of the brighter stars as well as of
the extremely faint members.

The distance of the Lesser Magellanic Cloud,
which appears very much like a star cloud de-
tached from the Milky Way, but which lies too far
from the plane of the galaxy to be considered a
portion of this girdle of the heavens, has been es-
timated at 30,000 light years. The Milky Way,
which defines the outer limits of our own sidereal
system, is generally believed to consist of several
branches lying one beyond the other. The nearer
portions, it is estimated, lie somewhere between
3,000 and 15,000 light years distant. Estimates
of the distance vary, according to whether or not
we include stars as bright as the sixth magnitude
among the hosts of stars that crowd these regions.
The vast majority of stars that form the star dust
of the galaxy range from the fourteenth to the six-
teenth magnitude. It is interesting to consider in
this connection that a star 10,000 times as luminous
as the sun would appear as a ninth magnitude
star at a distance of 20,000 light years. If we ad-
mit the presence of stars brighter than the ninth
magnitude in the nearer portions of the Milky
219

SPLENDORS OF THE SKY

Way we must either admit the presence of veri-
table giants in our sidereal system, stars that are
even more than 10,000 times as great as our own
sun in brilliancy, or we must limit the extent of
our stellar system and assume that the nearer star
clouds in the galaxy are but 2,000 or 3,000 light
years distant.

A class of objects far more numerous than the
globular star clusters that lie at immeasurable dis-
tances are the spiral nebulae, often spoken of as
the white nebulae, to distinguish them from the
green or gaseous nebulae. The idea that these are
external sidereal systems or "island universes" has
recently been revived. Many years ago, before
the day of large telescopes and of the spectroscope,
it was believed that all nebulae were star clusters
that could be resolved into separate stars by tele-
scopes of sufficient power, but when the larger tele-
scopes were obtained it was found that they could
not resolve some of the nebulae into star clusters,
and finally along came the spectroscope to prove
the truly gaseous nature of the green nebulae. As
to the nature of the spiral nebulae, however, we are
still in doubt. The spectroscope simply tells us
that they have a type of spectrum known as "con-
220

SPLENDORS OF THE SKY

tinuous," which, may belong to a solid or
liquid substance at high temperature or to an in-
candescent gas under high pressure. In this case
the spectroscope refuses to give us any informa-
tion.

We are familiar with the idea that our solar
system is evolved from a nebula, but the spiral
nebulae to which we refer are far too vast to give
birth to anything as simple as a single sun and its
satellites or even to arise, on the other hand, from
the close approach of two stars. Nothing less than
clusters of suns could be evolved from nebulas as
extensive as these. The evolution of groups of
stars from irregular gaseous nebulse, such as the
Orion nebula and the nebula surrounding the
Pleiades, is a process now going on before our
eyes. There are also moving clusters of stars, such
as the Taurus cluster, which is known to include
thirty-nine stars far exceeding our own sun in size
and splendor, that may have evolved from one
nebula. The latter star cluster has been very ex-
tensively studied and it has been estimated that in
something like 65,000,000 years it will appear as an
ordinary globular star cluster about twenty min-
utes in diameter, or two-thirds the diameter of the
221

SPLENDORS OF THE SKY

full moon, if it keeps up its present rate and di-
rection of motion.

If future investigations of spiral nebulae shall
disclose the fact that these formations that occur
in such great numbers are indeed far beyond the
limits of our own universe and form isolated stellar
systems, as now appears to be the case with the
Hercules star cluster, light may be thrown upon
some perplexing questions that arise concerning the
form and extent of our own sidereal system. Ac-
cording to some astronomers a spiral form for our
own stellar system fits in better than any other
with all the known facts concerning it.

222

CHAPTER XXIX

WONDERS OF THE GLOBULAR STAR CLUSTERS

INVESTIGATIONS made in the past few years
by Dr. Harlow Shapley at the Mount Wilson
Solar Observatory in regard to the distances and
distribution of about seventy globular star clusters
have brought results amazing even to the astrono-
mers themselves, accustomed though they are to
dealing with inconceivably great intervals of space
and time, and have greatly broadened our ideas of
the form and extent of the visible universe.

The following facts respecting these wonderful
star systems have been gleaned from several ex-
tremely interesting articles by Dr. Shapley, ap-
pearing in recent publications of the Astronomical
Society of the Pacific, which are preliminary to
complete discussions of the observations and re-
sults now in process of publication.
223

SPLENDORS OF THE SKY

Globular star clusters are, as the name implies,
symmetrically shaped, globular, in some cases ellip-
soidal, systems composed of thousands, possibly
hundreds of thousands, of individual stars strongly
condensed toward the centre. A few of these clus-
ters are visible to the naked eye as faint patches of
light, and the largest of them appear to fill a space
in the heavens less than that occupied by the full
moon.

The most noted of these are the great cluster in
Hercules in the Northern Hemisphere and Omega
Centauri and 47 Tucanse in the Southern Hemi-
sphere. The last named cluster is, in fact,
considered by some to be the finest telescopic object
in the heavens.

Indeed, the telescope makes a most striking
transformation in the appearance of these hazy
patches that we strain our eyes to see on a clear
night. A most brilliant assemblage of thousands
of suns, some deep red, others blue-white, gleam
and flicker, some with steady intensity, others with
the periodic pulsation of light that is characteristic
of the cluster variables.

It is the periodic waxing and waning of the light
of the cluster variables that has furnished the clue
224

SPLENDORS OF THE SKY

to the distances of the globular star clusters, though
the results have been checked by comparing the
apparent luminosities of other stars in the clusters
of the type of the red giant stars, such as Antares
and Betelgeux, and of the blue-white type of Vega
and Rigel with the known luminosity of these stars
at a standard distance from the sun.

The brightest stars in the globular clusters have
been found to have a surface temperature two or
three thousand degrees less than that of our sun,
and to be much redder in color. Emitting as much
light as they do, their volume must be very great.
They correspond to the red giants of the Galaxy.

The blue-white stars of the clusters are two or
three magnitudes fainter than the brightest red
stars, and among the bluer of these stars are found
the cluster variables which are similar in their
light variations to the noted Cepheid variables of
the Galactic system. Their light, color, spectrum
and velocity in the line of sight all pass through
a marked periodic variation in less than a day.

The maximum brightness is more than twice the

minimum, but the average brightness for a star of

this short period type has been found to be almost

exactly one hundred times the luminosity of our

225

SPLENDORS OF THE SKY

own sun. Between two and three hundred typical
variables whose periods range from a few hours to
one hundred days have been chosen from five glob-
ular clusters, the small Magellanic cloud, and the
Galaxy to form a curve which shows that the lum-
inosity of a variable star of this class bears a simple
relation to the period of its variation of light.

It has been found that the variables with periods
less than one day average one hundred times the
brightness of the sun, while those with the longest
periods average nearly ten thousand times the lum-
inosity of the sun and are rarely surpassed in
brightness by other stars.

The important result of this relationship is that
it gives immediately the distance of stars of this
type as soon as their apparent brightness and the
period of their fluctuations of brightness are known
and if the variables are located in globular clusters
it gives the distances of the clusters.

Investigations of the light variations of the Ce-
pheid variables in the small Magellanic cloud a
few years ago gave a distance of about 33,000 light
years for this object, which was about the greatest
distance the mind of man was asked to grasp until
the measurement of the distances of the globular
226

SPLENDORS OF THE SKY

clusters was undertaken by the same methods.

An apparently hopeless task has at last been ac-
complished and within the short period of two
years the distances of sixty-nine globular star clus-
ters have been measured with a probable error not
exceeding twenty per cent, of the values given,
which compares favorably with the degree of ac-
curacy obtainable in measuring by direct methods
the parallax of our nearer stellar neighbors within
a distance of one or two hundred light years.

One-fourth of the globular star clusters meas-
ured are more distant than one hundred thousand
light years. The two nearest, Omega Centauri and
47 Tucanae, are a little less than 23,000 light years
away.

The most distant so far known has a parallax
found by one method to be .000015 seconds, and
by another method .000014 seconds. Either value
would place it at a distance from us of considerably
more than 200,000 light years.

Possibly before the human race appeared upon
this planet the light that now reaches our eyes from
the most distant globular clusters had started on
its journey.

The individual stars visible in the globular clus-
227

SPLENDORS OF THE SKY

ters, though actually from 100 to 10,000 times more
brilliant than our sun, appear extremely .faint be-
cause of their great distance. Their apparent mag-
nitudes usually average from the twelfth to the
seventeenth, while the twenty-first is the limit of
visibility of the greatest telescope. Were our sun
in the nearest of the globular clusters it would be
too faint to be visible. The stars that gleam faintly
in these clusters are the giant suns of their sys-
tems.

How many more there are too faint to be seen
is unknown. The diameters of the globular clus-
ters average several hundred light years. There is
nothing in the neighborhood of our sun to compare
with this dense crowding of huge suns into a com-
paratively small space. Within a distance of
thirty-three light years of the centre of one typical
globular cluster there are to be found 15,000 stars
one hundred or more times brighter than our own
sun.

Within, the same distance of the solar system
there are known to be but four or five such stars.
Yet these individual stars in clusters are sepa-
rated by distances comparable to the distance that
separates our own sun from Alpha Centauri, more
228

SPLENDORS OF THE SKY

than four light years away, and no collisions be-
tween stars in globular clusters have yet been re-
corded, though, of course, all individual members
of the system are in motion.

The distribution of the globular clusters with
reference to the plane of the Galaxy or Milky Way
is most striking. Of the sixty-nine clusters exam-
ined (and the survey is considered complete within
one hundred thousand light years of the sun),
thirty-two are north of this plane and thirty-seven
south of it, and the average distance of the clusters
from the plane is about twenty-two thousand light
years. The centre of the system of clusters lies in
the Galaxy in the region of the dense star clouds
of Sagittarius and the diameter of the system is
at least three hundred and twenty-five thousand
light years, since two known clusters are separated
by this distance. The distance of our local group
of stars from the centre of this enormous system is
about sixty-five thousand light years.

A significant characteristic of the system of
globular clusters, Dr. Shapley points out, is the
equatorial belt between 10,000 and 12,000 light
years wide within which no globular clusters are
to be found. Within this belt are nearly all the
229

SPLENDORS OF THE SKY

stars listed in our catalogues, including the stars
visible to the naked eye as well as the gaseous nebu-
lae, diffuse nebulosities and open star clusters.
Outside the belt are the globular star clusters, the
Magellanic clouds, a few isolated stars and prob-
ably the spiral nebulae.

The explanation offered for the avoidance of the
equatorial belt by the globular clusters is their in-
ability to form and exist as compact organizations
in such an intense gravitational field.

The conclusions drawn from the facts so far dis-
covered are that all known objects in the heavens
belong to one enormous unit. The globular clus-
ters, Magellanic clouds and probably spiral nebu-
lae as well, though vast systems composed of thou-
sands, possibly hundred of thousands, of stars,
and moving through space with velocities of a
higher order than the average stellar velocity, are,
nevertheless, subordinate members of an organized
system whose form and extent the globular clusters
roughly outline.

The volume of this vast organized system is more
than 100,000 times that formerly assigned to the
stellar system.

The present location of our solar system in the
230

SPLENDORS OF THE SKY

universe is about three hundred light years from
the centre of a loosely formed moving star cluster
which lies just north of the plane of the Milky
Way and about half way from its centre to its
edge.

Man no longer places himself at the centre of the
universe, but finds it 65,000 light years away.

231

CHAPTER XXX

THE LIFE OF A STAR

^T^HE discovery of radioactive substances has
•*• radically affected many astronomical theories
bearing not only upon the age of the sun and its
planet family, but also upon the evolution of the
stars in general and the periods of time required
for the various stages of their development.

It is believed, moreover, that there are certain
properties of matter, as yet unknown as the revo-
lutionizing properties of radium were unknown
until the end of the nineteenth century, that will
solve the great problem of the source of the radiant
energy of the stars and explain why these bodies
pour forth into space light and heat and life-giving
energy at a lavish rate that has shown no signs of
abatement during hundreds of millions of years.
It is now known, thanks to the irrefutable cvi-
232

SPLENDORS OF THE SKY

dence furnished by radio-active substances, that
certain rocks containing uranium and the products
of its disintegration, helium and lead, have been
in existence for at least 1,500,000,000 years. How
long prior to this date our planet earth possessed
a surface crust is not known.

According to the testimony of geologists based
upon examination of the oldest fossil-bearing rocks,
well differentiated forms of life were in existence
on our planet a billion years ago.

During this inconceivably long interval of time,
according to astronomers, our sun must have main-
tained its energy of radiation virtually constant
though possibly varying cyclically within narrow
limits, for any marked increase or decrease in the
radiant energy of the sun would have made impos-
sible the continuous development of the various
forms of life that we know has taken place during
this period.

This fact has a direct bearing on the evolution
of the stars or their transition from one type to the
next. It is generally assumed that the helium or
bluish-white stars are the youngest and that they
change gradually to the next type, the hydrogen
or white stars, then to the yellow or solar type and
233

SPLENDORS OF THE SKY

finally to the orange and red stars that are ap-
proaching extinction.

The transition from one type to the next in
order is supposed to be attended by a decided
though gradual decrease in the light and heat-giv-
ing power of the star that amounts to several
hundred per cent, and would be fatal to life upon
any possible planet system of the star.

Astronomers have found from a consideration of
all known sources of energy, including radio-activ-
ity, that twenty-five million years is all that can
be allowed for the evolution of our sun from a
nebular state through the various spectral types to
its present condition, that of a star in the zenith
of its development.

This conclusion is, of course, not at all in accord
with any of the observed facts either of astronomy
or geology and simply shows that the true source
of the energy of the stars has not yet been dis-
covered.

Whatever the source of the solar energy may
prove to be, it has been sufficient to keep the spec-
tral type of our sun and its light and heat unvary-
ing, except within comparatively narrow limits,
for at least one billion years.
234

SPLENDORS OF THE SKY

For this reason astronomers are inclined to be-
lieve that the gradual transition from one star type
to another, granted such a transition does take
place, is a matter of hundreds of millions rather
than millions of years.

Since primitive forms of life first appeared upon
earth, our sun and its satellites have travelled more
than 100,000 light years, that is, as far as light
would travel in 100,000 years with its unimag-
inable velocity of 186,000 miles in a second, and
has experienced no catastrophe, though it has
doubtless journeyed far and wide through the star
streams of the Milky Way and seen the apparently
immovable constellations fade away in the distance
and new groupings take their place.

Though our own particular sun has so far es-
caped catastrophe the sudden appearance of Novae
is proof that all stars do not pursue the normal
course of evolution. As measured by man's stand-
ards of time temporary stars or Novae appear in-
frequently.

Novae of startling splendor such as Nova Aquilae
of the year 1918 are to be looked for only at inter-
vals of many years, running at times into centuries,
but less conspicuous temporary stars appear on
235

SPLENDORS OF THE SKY

an average of one in every three or four years.

Many of these do not even attain visibility to the
unaided eye at their best, but this is probably due
rather to their comparatively great distance than
to marked deficiency in actual luminosity at the
time of their outburst.

Since a year is but a moment in the life of a uni-
verse, Novae are by no means rare phenomena aside
from man's point of view. Since the time when
life on our planet was in its early infancy, possibly
1,500,000,000 years ago, 400,000,000 temporary
stars have burst forth, if the present rate of their
appearance was maintained in the past.

Four hundred million celestial catastrophes have
been enacted during this period. Nova Aquilae No.
3, the famous temporary star of 1918, has under-
gone in a few short months rapid and irregular
transitions of type such as normally would require
hundreds of millions of years if we judge by the
apparent permanency of type of our own sun dur-
ing the past 1,500,000,000 years.

At first appearance a brilliant blue-white star of

helium type, Nova Aquilae later appeared as yellow

as Capella and at another time more reddish than

Aldebaran, a late type star, though no regular pro-

236

SPLENDORS OF THE SKY

gression of type occurred, the changes being fitful
and irregular. Little is known yet concerning the
origin of Novae.

According to a suggestion of Prof. William H.
Pickering, Novse may arise from the impact of a
body of planetoidal dimensions with a star, assum-
ing that groups of such bodies are possibly drift-
ing through space in great profusion and the va-
rious members are separated by many millions of
miles. In the regions of the Milky Way, where the
star material occurs in greatest profusion, encoun-
ters would be most apt to occur.

There is the possibility, according to certain as-
tronomers, that our sun may have acquired part
of his planet family by capture. Our planet must
have possessed a surface crust for nearly two bil-
lion years at least. It has been proven that its in-
terior is not viscous, but as rigid as steel, and is
probably composed of material very closely resemb-
ling meteorites in composition.

The discovery of radio-active substances has ex-
ploded the idea that the only source of the inherent
heat of the earth is its originally high temperature
and that it is simply cooling off from a molten be-
ginning.

237

SPLENDORS OF THE SKY

The earth's temperature increases about one de-
gree in temperature for every 100 feet in depth.
This was formerly believed to indicate that the
earth was cooling off gradually. It is now
known that this heat arises from the disinte-
gration of radio-active substances in the earth's
crust, which sets free an enormous quantity of
heat.

It has been estimated also from the amount of
heat generated by these radio-active minerals at
the surface that the radio-active layer of rocks
probably extends only to a depth of thirty miles.
Beneath this crust, it is believed, there lies to a
depth of several hundred miles material similar to
the stony meteorites in composition, while the
earth's central core is of metallic composition, re-
sembling that of iron meteorites and is entirely free
from radium.

There is apparently nothing either in the pres-
ent composition of the earth or in its past condi-
tion throughout a period of over a billion and a
half years to particularly favor the idea that it
once formed part of a primitive solar nebula.
Neither is there reason to believe that the sun itself
was appreciably nearer to a nebular condition a
238

SPLENDORS OF THE SKY

billion and a half years ago than it is in the pres-
ent age.

There is a possibility that the fate of a Nova
may await our own sun. Its journeys through the
universe may at some future time carry it through
the more densely crowded portions of the Milky
Way, where some dusky mass may chance across
its path and suddenly terminate in a flaring out-
burst of light and heat the long career of the beau-
tiful yellow star that has so long supplied its planet
family with life-giving energy.

Under such circumstances all forms of life on its
satellites would be extinguished in the twinkling
of an eye. Barring this celestial catastrophe, all
present indications point to a future existence for
our little planet for many hundreds of millions of
years under the genial rays of a constant sun.

CHAPTER XXXI

light years distant from the earth, in
the vicinity of the Milky Way, is to be found
a class of stars remarkable for their deep red color.
If Sirius and Vega are the diamonds among the
celestial jewels, then these unusual stars are the
garnets and the rubies.

For many years these carbon stars or Type N
stars, as they' are technically called, appeared to
have no place in the evolutionary system of the
stars. A sequence in the development of all other
classes of stars had been well established, which we
will briefly outline in order to show the relation-
ship of the carbon stars to stars of other types.

Beginning with the gaseous nebulae, the accepted
order of stellar evolution is from nebulae to extinct
stars through a continuous series of changes, the
240

SPLENDORS OF THE SKY

first change being made from nebulae to bright line
stars, whose type of spectrum consists chiefly of
bright bands of unknown origin and a few bright
lines of hydrogen upon a faint, continuous back-
ground of rainbow color.

These stars are spoken of as the Type 0 stars or
the Wolf-Rayet stars, and they occur almost ex-
clusively in the Milky Way. The faint, continuous
background implies the presence of gases under
high pressure, which form the growing nucleus of
the star, while the bright lines and bands emanate
from incandescent gases under low pressure sur-
rounding the stellar core or possibly gases under
strong electrical excitement.

Gradually this type merges into the Orion, or
Type B, stars, in whose spectra the bright bands
have disappeared. The bright hydrogen lines be-
gin to diminish in intensity and gradually fade
away and the dark lines of helium and hydrogen
appear. This type is often called the helium type,
because of the prominence of the lines belonging
to this element. The continuous background is
particularly rich in blue and violet light, which
gives the stars of this class their beautiful blue-
white color.

241

SPLENDORS OF THE SKY

Rigel is a magnificent star of the Helium or
Orion type. The increase in the number of dark
lines in the stellar spectra from this point on im-
plies that the gases in the stars' atmospheres are
now absorbing more and more from the source of
light beneath the rays of the elements of which
they themselves consist, according to one of the first
laws of spectrum analysis.

The dark lines are for this reason often spoken
of as absorption lines, and they appear dark only
by contrast with the brilliant background of con-
tinuous light upon which they are projected. As
the composition of the stellar atmosphere changes
with the advance in evolution, absorption lines and
bands and flutings of various different elements
appear, but to a given element always belongs the
same set of lines and its own position in the spec-
trum.

As the Orion, or Type B star, gradually changes
to the Sirian or Hydrogen type, the lines of helium
diminish in intensity, while the hydrogen lines in-
crease and finally become the most conspicuous
feature of the type. Technically this group is re-
ferred to as the Type A stars. The name Sirian is
given to it also from the fact that the most bril-
242

SPLENDORS OF THE SKY

liant of all stars, Sirius, is an illustrious member.

These stars are noted for the intense whiteness
of their light and their high temperatures, as well
as the low density of their atmospheres. In this
class the metallic lines of the solar spectrum also
begin to appear faintly, and in the succeeding type
known as the Calcium, or F type, they show more
strength, though they still remain inferior to the
hydrogen lines. The calcium lines have become
conspicuous and characterize the type.

Canopus is a most noted member of this group.
The color of the stars from this point on is tinged
more and more with yellow. The next step in stel-
lar evolution is that occupied by our own sun.
Stars of this class, are called Type G stars. In
these the hydrogen lines are still very con-
spicuous, but equalled in intensity by many of
the metallic lines, which now appear in great
numbers.

Capella is also a prominent member of this class.
This stage probably represents the zenith of stellar
development, the middle-aged period of star life.
From this point the stellar spectrum becomes more
and more reddish as the rays of shorter wave length
become absorbed more and more in the gases of the
243

SPLENDORS OF THE SKY

star's atmosphere, which is gradually increasing in
density.

Type K, that immediately follows the solar type,
is characterized by spectra in which the hydrogen
lines are now becoming fainter than some of the
metallic lines. These stars are orange in color.
An illustrious star of this type is Arcturus. Even
before this stage there is manifest a marked ten-
dency of the stars to divide into giants and dwarfs,
which becomes still more pronounced in the fol-
lowing class of red stars of Type M, which comes
at the end of the process of evolution.

The dwarfs of this class are so feebly luminous
that they seem to mark the last stage before ex-
tinction and the advent of dark stars.

A decided decrease in the star's temperature is
evidenced by the appearance of flutings and bands
in the spectrum, due to metallic compounds, chiefly
of titanium oxide. Though it is generally considered
that the dwarf red stars of this class are nearing
extinction, many believe that the giants of Type M,
of which Antares and Betelgeux are well known
examples, are stars of low density that are grad-
ually increasing in temperature and passing
through the evolutionary process in reverse order.
244

SPLENDORS OF THE SKY

After reaching the white-hot hydrogen or helium
stage it is held that they will pass once more
through the solar stage to the type of dwarf red
stars.

Though the direction of progression through the
various types is a matter of some uncertainty for
certain stars, the fact that there is a gradual change
in the life history of the average star as outlined
above appears to be beyond question. Type merges
into type through gradations so slight that it is
difficult to say where one type ends and the next
begins.

Until recently stars of the carbon type appar-
ently had no place in this scheme of evolution. A
gap seemed to separate them from stars of other
types. Though presenting some points of resemb-
lance to the red stars of Class M, they presented
as many points of difference. Both in general dis-
tribution in the heavens and in type of spectra they
refused to be classified with the M stars.

The carbon stars are all extremely faint stars,
due to their tremendous distance from us, even the
brightest of the class being barely visible to the
naked eye. They show a most marked preference
for the plane of the Milky Way, never being found
245

SPLENDORS OF THE SKY

at any great distance from it, while the red stars
of Type M are noted for their nearly uniform dis-
tribution in space, being found as often near the
poles of the Milky Way as in its plane.

Some of the M stars are our close neighbors,
while the brightest of the carbon stars show no
parallax or motion across the line of sight. Their
spectra are characterized by the presence of dark
bands due to carbon compounds, which fade away
toward the blue end of the spectrum, while the
spectra of the M stars have bands of titanium oxide
sharply defined on the violet side and fading to-
ward the red.

In recent years the carbon stars have been care-
fully studied, and it now appears to be well estab-
lished that they can be traced back in evolution to
stars of the same type as the sun along an inde-
pendent branch.

The discovery of a new type of star, called Type
R, that appears to come intermediate in develop-
ment between the solar and carbon stars, possess-
ing some of the characteristics of each, has led to
this conclusion.

Stars of this new type supply the miss-
ing link necessary to trace the development
246

SPLENDORS OF THE SKY

of a solar star into a carbon star, or possibly the
reverse.

Spectra of more than sixty stars belonging to
this intermediate class have been investigated.
Many of them were formerly classified as carbon
stars, though some have a decidedly yellowish tinge
and partake strongly of the features of the solar
stars.

There are then two paths that a star may follow
after it has reached the point in its development
known as the solar stage. Differences in the rela-
tive amounts of certain elements in the atmosphere
of stars may determine which path shall be fol-
lowed after this point, whether a star shall pass
through Type K to a red star of Type M, whose
spectrum is dominated by compounds of titanium
oxide, or through the new Type B stars to red
carbon stars, whose spectra show the distinctive
bands of carbon compounds.

That the carbon stars can be linked to the evolu-
tionary chain of stellar development is particularly
satisfying to the astronomer, for it shows that all
stars can be included in one great system of evolu-
tion and pass from one type to the next gradually
as they increase in age and development.
247

CHAPTER XXXII

DWARF STAR HOTTER THAN THE SUN

HE existence of a tiny body two or three hun-
dred per cent, hotter than the sun, yet with
a diameter only one-hundredth as great, situated
only thirteen light years distant from the earth,
and, therefore, one of our nearest stellar neigh-
bors, is a most interesting recent discovery of
astronomy.

Van Maanen, of the Mount Wilson Solar Ob-
servatory, noted the extremely high proper motion,
or motion across the line of sight, of this star, and
concluding, therefore, that it was most probably
comparatively near to our solar system, made a
determination of its parallax from a series of six-
teen photographic plates.

The value found, two hundred and forty-four
248

SPLENDORS OF THE SKY

thousandths of a second of arc, is very large, the
greatest parallax known, that of Alpha Centauri,
the nearest star, being only seventy-six hundredth^
of a second. There are in all hardly a score of
stars that have larger parallaxes than this small
body and are, therefore, nearer to us.

The motion of this star across the heavens is also
exceptionally great, amounting to slightly over
three seconds of arc a year. It is, therefore, the
most rapidly moving star discovered since Bar-
nard's Runaway Star of 1916, which is also a very
near neighbor of ours, six light years distant and
a very faint body as well, possessing only five ten-
thousandths of our own sun's brightness.

It is, however, a whole stellar magnitude, or two
and a half times brighter than the newly discovered
sun, which has, accordingly, only one five-thou-
sandth part of the luminosity of our own sun and
is one of the faintest stellar bodies known.

The most surprising fact discovered about this
diminutive sun is that its faintness is due to its ex-
tremely small size and not to failing light. This is
known from the fact that its type of spectrum is
the Calcium or F type, which belongs to bodies at
least two or three times hotter per unit area than
249

SPLENDORS OF THE SKY

our own sun. The color of this small sun has also
been determined and is white, indicating a high
surface temperature.

Since the light-giving power of this star relative
to the sun is known, and since it radiates two or
three times more brilliantly per unit area, it is
possible to determine the actual size of its radiat-
ing surface and therefrom its diameter relative to
the sun's diameter.

This diameter is found to be approximately one-
ninetieth of the sun's diameter, or nine thousand
five hundred miles. As far as size goes, it might,
therefore, take its place among the smaller satel-
lites of our sun, the terrestrial planets Earth and
Venus being scarcely inferior to it in size. Yet
this dwarf sun rushing through space is intrinsic-
ally a far hotter body than our own sun, judging
from its type of spectrum.

Strange to say, the mighty Canopus, estimated
to be at least ten thousand times more brilliant
than the sun, has identically the same type of spec-
trum.

Since the dwarf sun recently discovered has
only one five-thousandth part of the light-giving
power of the sun, we have here two stars of iden-
250

SPLENDORS OF THE SKY

tically the same temperature per unit of surface
area, differing at least fifty million times in lu-
minosity. Such is the disparity existing in the
actual sizes of the suns of the universe !

The only escape from the above conclusions
would lie in considering that stars with identically
the same type of spectrum do not radiate with equal
intensity. It is assumed to be one of the funda-
mental laws of spectrum analysis, however, that two
bodies with identical types of spectra radiate with
equal intensity per unit of surface area.

How such a tiny sun could continue to radiate
light and heat at the lavish rate indicated by its
type of spectrum for any great interval of time is
a problem. Most faint stellar bodies so far discov-
ered in the vicinity of the sun belong to the group
of nearly extinct dwarf stars low in surface tem-
perature and decidedly reddish in hue. This bril-
liant little sun of calcium type, whiter and hotter
than our own sun, is a marked exception.

It is by far the smallest body of its type so far
discovered. In absolute magnitude it is exceeded
by all known stars with the exception of a faint
companion star of Alpha Centauri. It is possible
that this tiny sun may possess still more diminutive
251

SPLENDORS OF THE SKY

satellites of its own and dispense its light and heat-
giving rays to these smaller bodies.

Within our own solar system, at least, it is the
exception rather than the rule for bodies to be un-
attended by satellites. Were this small sun at-
tended by any body at all comparable to it in size,
however, its presence could be detected by its dis-
turbance of the bright body.

How many of these suns of planetary size exist
in the universe it is impossible to estimate. It is
only the very nearest of such stars that can pos-
sibly be detected. At a distance of only thirteen
light years the star discovered is invisible in small
telescopes. Were it much further removed, it
would be invisible even in large telescopes. Mil-
lions of these diminutive suns may exist in far dis-
tant parts of the universe, hopelessly beyond our
reach. It is only the light of exceptionally large
suns that reaches our eyes from far distant realms.

Since the number of stars of the thirteenth ap-
parent magnitude to which this sun belongs is
estimated at something like two million, it can be
judged that only through some marked peculiarity
would such a star be singled out for observation.

In general the faintness of a star is assumed to
252

SPLENDORS OF THE SKY

be an indication of great distance. Very distant,
faint stars appear immovable in the heavens,
though they may be in reality in rapid motion
through space. It is, therefore, convenient in many
kinds of astronomical work to determine the posi-
tion of some object under observation relative to
one of these fixed " landmarks " of the sky.

It is only occasionally, as in the present instance,
that one of these points of reference shows any
individual motion and thereby calls attention to its
unusual nearness. In observing the stars the as-
tronomers have given their attention first to the
more brilliant and conspicuous stars. The fainter
and less noticeable stars have received less atten-
tion and have largely escaped detailed investiga-
tion because they are far more numerous than the
brighter stars and to examine them with anywhere
near the same degree of thoroughness is a manifest
impossibility.

The brighter a star the more likely it is to be
classified and studied. It is only in recent years
with the advent of powerful telescopes and photo-
graphic methods of observations that the careful
study of the fainter stars has been undertaken at
all exhaustively. Interesting and important facts
253

SPLENDORS OF THE SKY

regarding the fainter stars are now being slowly
accumulated in spite of the fact that their numbers
run into the millions and they are observable only
with the larger instruments.

The importance of the discovery of all facts
possible concerning the smaller as well as the
larger suns of the universe is very great, since by
this means light is thrown upon many puzzling
problems associated with the origin and evolution
of the stars, the source of their energy and their
varied physical characteristics as well as their num-
bers and distribution through space.

It is a decided addition to astronomical knowl-
edge to know that it is possible for a body no
larger than our own planet Earth to maintain a
surface temperature far hotter than the sun,
though how this tiny sun keeps up its tremendously
high temperature is inconceivable unless there is
assumed to be some unknown source of the radiant
energy of the stars.

254

CHAPTER XXXIII

PHOTOGRAPHY OF THE HEAVENS

photography of the heavens has become of
such importance in all branches of astronomy
that there is hardly an observatory to-day that is
not provided with facilities for carrying on this
valuable work.

Every year hundreds of photographic plates are
exposed in the study of celestial objects, and prob-
ably not a day passes that the sun is not photo-
graphed at a number of observatories all over
the world. The discoveries already made by pho-
tography have more than repaid the efforts thajb
have been made to bring celestial photography to
the highest degree of efficiency. Since the photo-
graphic plate is particularly sensitive to the violet
end of the spectrum, every advantage has been
taken of this fact, and by means of specially dyed
255

SPLENDORS OF THE SKY

plates it has also been possible to photograph be-
yond the visual limit, even in the red end of the
spectrum.

In astronomical photography the telescope takes
the place of the camera and the photographic plate
takes the place of the observer at the eye end of
the telescope.

It is of the greatest importance in such photo-
graphic work to accurately compensate for the
effect of the earth's rotation on its axis, and this is
done by means of the clockwork that is connected
with all large telescopes, so that the axis of tho
telescope may be given a motion opposite to the
direction of the earth's rotation. In this way all
objects in the field of view are kept immovable with
respect to the eye or photographic plate, and the
telescope "follows" the object in its apparent west-
ward motion. Anyone who has looked through a
telescope when the clockwork is not running knows
how rapidly an object will drift out of the field on
account of the earth's rotation. It is customary
when photographs of the heavens are taken to fol-
low the object with the eye as well, by means of a
visual telescope attached to the photographic tele-
scope. By this means any slight irregularity of
256

SPLENDORS OF THE SKY

motion can be at once detected and corrected for
during the time of exposure. In exposures of sev-
eral hours * duration the rate of the clock might
affect the motion of the telescope sufficiently to
render the photograph worthless. Exposures of
four or five hours are frequent, and in the photo-
graphy of a magnificent spiral nebula in Canes
Venatici, made at the Mount Wilson Observatory,
an exposure of more than ten hours was given.

In photographing comets which have a percep-
tible motion of their own during the time of ex-
posure the telescope is made to ' ' follow ' ' the comet,
that is the comet is held immovable in the field of
view of the telescope, and star images in the field
then appear as short trails of light instead of the
sharply defined round dots they would other-
wise be.

Excellent comet photographs have been taken
since photography of the heavens has become gen-
eral and research work into the nature of comets is
done now almost entirely by means of photography.
A large number of plates are examined and com-
pared and the entire history of a comet can be
studied in this way from the time when it appears
as a faint nebulous object, through the interesting
257

SPLENDORS OF THE SKY

phase when it is approaching or receding from
the sun and developing an extensive tail, until it
again departs into the depths of space. It can be
detected on the photographic plates long after it
is beyond the reach of the most powerful tele-
scopes visually.

Many comets as well as asteroids and faint satel-
lites are now discovered by photography. Plates
are exposed to various parts of the heavens where
the existence of such objects is suspected and the
earth's motion is exactly balanced by means of the
siderial clock so that when the plates are devel-
oped each star registers its position by a clear,
sharp dot proportional to its brightness. If any
moving object is within the field it will appear on
the plate as a short trail of light proportional in
length to its motion during the time of exposure.
In this way it is easily distinguished by its appear-
ance. A host of asteroids have been discovered by
this method and the some comets are found in
the same way. Halley's comet at its return in
1910 was first detected upon the photographic
plates. Objects too faint to be seen in the largest
telescope will cast enough light upon a photo-
graphic plate in several hours' exposure to reveal
258

SPLENDORS OF THE SKY

their presence in the heavens. Several satellites dis-
covered photographically have never been seen ex-
cept on photographic plates.

These are too faint to be visible to the human
eye aided by the most powerful telescope, and we
owe to photography alone our knowledge of their
existence. The eye surpasses the camera, however,
in observation of the finest details of planetary
and lunar phenomena, and it has been said that
photographs taken with powerful telescopes do not
show the detail observable visually.

The study of all solar phenomena has been con-
sidered of such importance that there now exist
observatories that make this their chief work. A
noted observatory of this class is the Mount Wilson
Observatory at Pasadena, Cal. Wonderful progress
has been made here photographically. The spectro-
heliograph was invented here by Dr. Hale and is a
device for photographing the sun by the light of a
single wave length such as a calcium or hydrogen
ray. The spectro-heliograph acts as a screen to cut
off all light except that of a certain line in the
spectrum, and extremely valuable and interesting
photographs of the sun have been obtained by this
method.

259

SPLENDORS OF THE SKY

On total solar eclipse expeditions the photo-
graphic outfit is of prime importance. At this
time only is it possible to obtain photographs of
the mysterious corona that is only one-tenth as
bright as full sunlight and therefore masked at all
other times by the glare of the sun.

A striking instance of the value of photography
to astronomy is the discovery made by Prof.
Barnard through the examination of photographic
plates of a star of the eleventh magnitude in the
constellation Ophiuchus that has the enormous
motion through space of at least ten seconds of arc
a year. This puts it first in the class of ' ' runaway
stars/' which, according to the late Prof. New-
comb, have a motion that not all the matter in the
universe could control. The greatest known annual
proper motion, as it is called, has been 8.7 seconds
until the discovery of this star, but very few stars
are known that have a proper motion greater than
one second, and the average is far below one sec-
ond. This discovery was confirmed by the study
of photographic plates at Lick and Harvard dating
back as far as 1888. We have here a specific case
of the value of photographic records.

The astronomers of to-day are storing away
260

si

; ?

IP

S >

SPLENDORS OF THE SKY

upon photographic plates material that will lead
to the discoveries of the future. If such valuable
records could have been left to us by our ancestors
the knowledge of the wonders of the heavens would
be advancing to-day by leaps and bounds. In all
research work into the nature and structure of the
universe photographic records are invaluable. By
comparison of plates taken many years apart
changes become evident. It is believed that nebulae
may possibly change greatly in form in the course
of a few hundred years and that the brightness
of many stars, aside from the class of variables,
may have changed appreciably in this time.
Photography is by far the best means of solving
such questions as well as many others of a similar
nature. Four-fifths of all spectroscopic work, it is
estimated, is now done photographically and done
far better than it would be possible to do it visu-
ally, owing to the light gathering power of the
sensitive plate. Spectra of stars that would never
be seen otherwise can be detected by this means.

Last but not least is the fact that the wonders
of the telescope, the nebulas, star clusters, planetary
markings, corona and numerous other equally inter-
esting phenomena would never be seen except by
261

SPLENDORS OF THE SKY

a few if it were not for photography. At the
different observatories in this country, Lick, Har-
vard, Yerkes, Mount Wilson and many others, not
to mention those abroad, magnificent photographs
have been taken which are at the disposal of all
of us through our schools and libraries. To be
sure the result may be that many of us are only
the more desirous to see for ourselves the beauties
of the heavens and to explore the depths of space,
and it is to l)e hoped that the day may come when
each city will have an observatory at the disposal
of all who may care to use it. It is surprising
what even a six-inch telescope will reveal and we
do not need a 40-inch Yerkes telescope to enjoy
the wonders and beauties of the universe.

262

CHAPTER XXXIV

THE PHOTOGRAPHIC PLATE — THE ASTRONOMER'S EYE

fT^HE astronomer of to-day spends very little
••• time gazing at the stars through the telescope.
His place at the eyepiece has been taken by that
silent sentinel of the sky, the photographic plate,
which is on duty in some instances for hours at a
time gathering precious rays of light from star
or nebula that the human eye would search for in
vain. We find the modern astronomer oftener in
the dark room, the physical research laboratory,
the instrument shop or the computing room than
at the telescope. His discoveries are now rarely
made by direct observation of the heavens. They
result chiefly from careful examination and meas-
urement of photographs.

Photographs taken on June 7, 1918, at the Har-
vard College Observatory, where the photography

263

SPLENDORS OF THE SKY

of the heavens is carried on regularly and systemat-
ically every clear night, show that the initial stages
in the rapid increase in brightness of the magnificent
new star of 1918, Nova Aquilae No. 3, were recorded
by this means even before the star became visible
to the naked eye. When the brilliancy of the nova
on the night of June 8 amazed all observers the
astronomer's first thought was to obtain photo-
graphs as quickly as possible of both the star and
its spectrum and then examine its past history.
This, it was found, had been recorded for fully
thirty years on photographic plates stored away at
the Harvard Observatory, where many a valuable
astronomical discovery has been made by means of
photography.

A never failing eye is kept on the heavens in
the form of the photographic plate, and changes
that take place there hour by hour, day by day
or year by year may be recorded for future refer-
ence. Photographs taken in our day may be of
priceless value to future generations of astrono-
mers, for by comparison of photographs taken at
intervals of ten, fifty or one hundred years impor-
tant discoveries may be made concerning the mo-
tions of the stars through space, changes in the
264

SPLENDORS OF THE SKY

structure of the nebulae, the appearance and dis-
appearance of temporary stars, and all the varied
and wonderful phenomena of a universe of count-
less suns at all stages of development.

Celestial photography is beset with many diffi-
culties and presents many problems, some depend-
ent upon the nature of the plate and its develop-
ment, others upon the instrument.

Photographic plates are subject to many imper-
fections. False stars frequently appear after ex-
posure of the plate. It is not known whether these
appear in the process of development or are due to
defects in the plate itself. They are usually easily
distinguished from true stars, however. In a few
rare instances defects in the plate have been taken
for asteroids or comets, which usually appear as
short trails.

The photographic discovery of an asteroid with
a satellite by Prof. Wolf of Heidelberg, announced
in the spring of 1918, caused considerable interest
nt the time, as it was most unusual and unexpected.
Diligent search by other astronomers and the ex-
amination of additional plates taken of the same
^egion failed to confirm the discovery, and it was
finally decided that the "satellite'' was possibly
265

SPLENDORS OF THE SKY

an imperfection of the photographic plate, though
the discovery of the asteroid was confirmed.

The photographic images of the stars are not of
uniform shape and density all over the plate. They
are usually perfectly round and of even density in
the centre of the plate, Lut near the edges they are
elliptical or elongated and irregular in density, a
fact that makes their accurate measurement very
difficult. Star images are, in fact, affected by
many different factors, depending upon the kind
of plate used, length of exposure, temperature and
developer, as well as the telescope itself, whether
reflector or refractor, of short or long focal lengths.

It is a well known fact, however, that the sizes
of the star images on the same plate vary with the
brightness of the stars photographed. The brighter
the star the greater the diameter of its image on
the plate. This affords a method of determining
the relative brightness of the stars photograph-
ically that is more accurate than the visual method.
The human eye is more liable to error than the
photographic plate, since the individual peculiari-
ties of the eye are many and subject to great
uncertainty. Another advantage of the photo-
graphic method for finding the relative brightness
266

SPLENDORS OF THE SKY

of the stars lies in the fact that stars too faint
to be seen appear on the photographic plate even
with an exposure of short duration, while a longer
exposure brings out additional stars.

The photographic plate, as is well known, is
particularly sensitive to rays of short wave length,
the blue and violet rays, while the eye is, on the
contrary, susceptible to the rays of long wave
" ength, the red, orange and yellow rays. A very
important application of this principle is made in
determining the color of stars so excessively faint
that they cannot be studied with the spectroscope.
The physical condition and stage of development
of a star are closely associated with its color and
therefore any knowledge that may be gained in
regard to the color of faint stars will add mate-
•iially to our knowledge of them.

If an excessively faint star appears much
brighter photographically than it does visually
it is evident that it is particularly strong in blue
or violet light ; that is, it is an early type or young
^tar. On the other hand, if the star is fainter
photographically than it is visually it is strong
in red or orange light, to which the eye is par-
ticularly sensitive. Such a star is a red or late
267

SPLENDORS OF THE SKY

type star. This difference between the visual and
photographic brightness of a star is called its color
index, and it is of great value in classifying faint
stars, the only clue in fact that the astronomer
possesses to their age and physical condition. It
indicates the relative proportions of light of dif-
ferent wave lengths emitted by the star and the
nature of its atmosphere.

By the use of specially dyed plates or color
screens it has become possible to shut off the
rays of violet or blue light from the photographic
plate and make it sensitive to the same rays that
affect the eye. In this way the photographic plate
becomes the equivalent of the human eye with the
added advantage of being free of the individual
peculiarities of vision that make visual estimates
of the relative brightness of the stars so uncertain.
The stellar magnitudes determined with these spe-
cially prepared plates are spoken of as photo-visual
magnitudes.

The relative magnitudes of the stars are thus
expressed in three different scales, the visual, the
photo-visual and the photographic. The first two
should be approximately equal. The photography
of the heavens with the photo-visual rays opens a
268

SPLENDORS OF THE SKY

comparatively new field of investigation and ex-
periments with various methods of dyeing plates
or screening off certain rays may yield some valu-
able results in the future.

269

CHAPTER XXXV

THE STORY OF A RUNAWAY STAR

^TT*HE recent discovery of a rapidly moving star
•*- in the constellation Ophiuchus aroused con-
siderable interest in the astronomical world. The
unusual motion of this star was detected by
Prof. Barnard at the Yerkes Observatory in 1916
from a comparison of a series of photographs taken
at Yerkes and reaching back as far as 1894. It
was confirmed by numerous plates taken at Har-
vard Observatory, the earliest of which dates back
to 1888.

In one year this star moves about twice as far
as the average star does in a century. It has the
enormous proper motion, that is, motion perpen-
dicular to the line of sight or across the sky, of
10.3 seconds a year. If a star moves two-tenths of
270

SPLENDORS OF THE SKY

a second a year it is considered to have a large
proper motion.

So slight is the change in the relative positions
of the vast majority of stars from year to year
that after the lapse of a thousand years the skies
are practically the same in their general appear-
ance.

The smallest displacement that a keen eye can
detect in the position of a star when unaided by a
telescope is three minutes of arc, and the average
cross motion of a star in a thousand years does
not exceed one minute.

The extremely few stars that form notable ex-
ceptions are generally spoken of as " runaway
stars. ' ' The faint star in the southern hemisphere
known only by its catalogue name of Cordoba Zone
5th No. 243 formerly headed the list of runaway
stars with a proper motion of 8.70 seconds, and
next in order is the famous runaway star Groom-
bridge, 1830, with a cross motion of 7.07 seconds.

So rapid is the motion of Barnard's star that it
will cover an arc of fully three degrees, just the
length of the belt of Orion, in a thousand years.
If the majority of stars had a motion at all com-
parable to this the appearance of the constella-
271

SPLENDORS OF THE SKY

tions would be entirely changed in a few centuries.
If the two stars spoken of as the " Pointers " in
the Great Dipper had a proper motion as high as
ten seconds a year this famous constellation would
lose its distinctive shape in considerably less than
a thousand years.

Many stars have a common drift through space,
but it is very rare for all the chief stars of a con-
stellation to share the same direction of motion.
Of the seven stars that form the outline of the
Great Dipper five are moving in the same direc-
tion, but the brighter star of the Pointers and the
star at the end of the handle are moving in an
entirely different direction.

In the short time that has elapsed since its dis-
covery determinations of the parallax, radial ve-
locity and type of spectrum of the new star have
yielded some interesting results. As seen in the
36-inch Lick refractor it is a faint, orange-colored
star of the 1(% magnitude, and it has the type
of spectrum that is characteristic of stars far ad-
vanced in evolution. It is what is known as a
" dwarf " star of the type M. The variable star
Alpha Herculis is a " giant " of the same class.
The spectra of stars of type M are strangely fluted
272

SPLENDORS OF THE SKY

in appearance, because of the presence of titanium
oxide. It is not known as yet why stars of this
type show spectra so dominated by this one sub-
stance.

The shifting of the lines of this star's spectrum
toward the blue indicates that it is approaching
the solar system, and measurements of the amount
of this shift indicate a rate of approach in the
line of sight of about sixty miles a second. It is
a well known fact that if a star is receding from
the earth the lines of its spectrum shift toward the
red end of the spectrum and if it is approaching
they shift toward the blue. So it is by the meas-
urement of the lines in this star '$ spectrum that we
can tell it is coming toward us at the rate of sixty
miles a second.

Some determinations of the parallax of this star
have been made, and apparently it is the largest
known, with the exception of the parallax of Alpha
Centauri, the nearest star. In other words, Bar-
nard's new star is probably our second nearest
neighbor, and, its brightness is found to be five
ten-thousandths that of the sun, which makes it
one of the faintest stars so far known.

It seems to be characteristic of " dwarf" stars
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SPLENDORS OF THE SKY

of this type to have high velocities. There is a
decided tendency for stars to increase the speed of
their journey through space as they increase in
age, although such a velocity as this star possesses
is far above what we should expect of a star of
its class. It seems to be a true runaway star.
Since faint stars have not yet received as careful
scrutiny as has been given to the brighter members
of the stellar system, possibly we may find in time
that there are faint stars nearing extinction that
travel through space with a velocity far exceeding
any to which we have been accustomed.

It is a peculiar fact that nearly all types of
stars show a tendency to crowd toward the plane
of the Milky Way. Type M, to which the newly
discovered star belongs, is a noted exception to
this rule. Stars of this type show a spherical dis-
tribution of space and are just as likely to be
found at the poles of the Milky Way as in its
plane. It has been suggested that dwarfs of this
type with extremely high velocities such as Bar-
nard's star possesses may have acquired their enor-
mous speed while falling in toward the plane of
the Milky Way from great distances without.

Runaway stars have also been spoken of as
274

SPLENDORS OF THE SKY

visitors passing through our stellar system from
regions beyond. It has been said on good authority
that there is not sufficient matter in our stellar
system to control the motion of such a runaway
star as Groombridge, 1830.

In the short time that has elapsed since the
detection of the enormous proper motion of the
new star some very interesting facts have been
well established. This star is in all probability our
second nearest neighbor at a distance of about six
light years. Its luminosity is five ten-thousandths
of the sun, making it one of the least luminous of
all stars so far discovered, and it is, as we would
expect, a star of most advanced type, bordering
close upon extinction.

275

CHAPTER XXXVI

MEASURING STAR DISTANCES

>TpHE parallax of a star is its apparent displace-
•- ment in the sky due to the change in the
earth's position in its orbit. It is the angle that
93,000,000 miles, the distance from the earth to
the sun, subtends at the star. Viewed from the
vast majority of the stars this base-line shrinks
to an immeasurable point.

The direct measurement of the parallax of the
stars by the triangulation method, by which the
star's displacement at different times of year is
determined either photographically or visually
with reference to faint stars so distant as to have
zero parallax, is possible only for a few stars near
the solar system. The distances of nearly a thou-
sand stars have been determined with more or less
accuracy by this method.
276

SPLENDORS OF THE SKY

The astronomer is here attacking a problem
simple in principle but possessing great practical
difficulties due to the minuteness of the angle to
be measured. The largest known parallax, which,
of course, belongs to the nearest star, is only sev-
enty-eight hundredths of a second. This value of
the parallax corresponds to a distance of about
twenty-five trillion miles from the earth.

Since to express the distance of the stars in
miles would be as cumbersome and meaningless
as to express the distance from the earth to the
moon or neighboring planets in inches, a new unit
for the measurement of stellar distances has been
found in the velocity of light. In one second light
travels 186,000 miles j in one year it travels nearly
six trillion miles. The distance light travels in one
year is spoken of as the light year. The distance
of over twenty-five trillion miles that separates
us from the nearest star is equal to four and one-
third light years, and the rays of light leaving this
star take four and one-third years to reach the
earth.

There are about twenty stars with parallaxes
exceeding 0."2. A parallax of 0/2 corresponds to
a little over sixteen light years. There are about
277

SPLENDORS OF THE SKY

twenty stars known to be within this distance of
the sun, and their distances have been determined
by direct measurement of their parallaxes with an
error that is less than 25 per cent, of the quantity
measured.

A directly measured parallax of ".02 has very
little value, because unavoidable errors of in-
struments may be nearly as large as the quantity
to be measured. This parallax corresponds to a dis-
tance of about 160 light years, and the tremendous
extent of the universe can be judged from the
fact that scarcely one hundred stars have paral-
laxes greater than ".02. It is safe to say that no
reliable measures of the distances of the stars
lying beyond this point can be made by direct
measurements of their parallaxes.

The triangulation method is long and tedious
and care must be taken to avoid systematic as
well as accidental errors. The finally determined
parallaxes are usually the result of a large number
of independent measurements.

There are a number of indirect methods of find-
ing the parallax of the more distant stars. The
most important of these is probably the one that
deals with the proper motions of the stars. The
278

SPLENDORS OF THE SKY

stars are all moving1 in various directions and at
different rates. The actual motion or space motion
of a star, as it is called, can be divided into two
components. One is the motion in the line of
sight toward or from the observer. This is called
the radial velocity and can be determined by means
of the spectroscope. The other component, the
angular motion across the line of sight, is called
the proper motion of the star. In general the
nearer a star is to the earth the greater will be its
proper motion.

While parallax is a displacement in a star's
position due to a change in the observer's posi-
tion as the earth moves around the sun, proper
motion is the displacement in the star's position
due to its own motion across the line of sight,
and, of course, the nearer the star is to the observer
the more it appears to be displaced and the greater
its proper motion. A star that has no measurable
proper motion is at great distance from the earth.

"When both the radial velocity and the proper
motion of a star are known its distance from the
earth can be determined, for its cross-motion then
becomes known both in angular measure and miles
per second. Moreover, the distances of moving
279

SPLENDORS OF THE SKY

groups of stars or moving star clusters can be
found when the radial velocity of any one star in
the group is known, since the stars are all moving
at the same rate in the same direction. The extent
of the group, in light years, the distances sepa-
rating individual stars, as well as the distance of
the group from the earth, become known as soon
as the common proper motion of the stars and the
radial velocity of one of the group has been
determined.

When the distance of a star is known, its abso-
lute magnitude or luminosity, compared with the
sun's luminosity, can also be found from a simple
relation between the parallax and the apparent
and actual brightness of the star.

Some important results arising from investiga-
tions of the proper motions and radial velocities of
stars have been the discovery of star drift or star
streaming, and the direction and amount of the
sun's motion through space as well as actual de-
termination of distances in light years for indi-
vidual types or groups of stars such as the Cepheid
variables, the Orion stars, the giant red stars, the
Pleiades, the Ursa Major group, and others.

The motion of the sun through space also fur-
280

SPLENDORS OF THE SKY

nishes a valuable base line for the determination
of the distances of the stars. This motion amounts
to nearly four hundred million miles a year and
is, of course, increasing year by year. If the
motion in one year gives too small a base line the
motion in ten years or one hundred years can
be used. In applying this method the individual
motions of the stars have to be taken into account,
but it is customary in computing the average dis-
tance of a certain class of stars to go on the assump-
tion that the sum of the individual motions of
stars moving in all directions will compensate each
other and the result will be the same as if all
the stars were at rest.

The average of the motions of a large number of
stars across the line of sight will total zero and
the average of their motions in the line of sight
will be made up of their own motions plus the
effect of the sun's motion, which is spoken of as
the parallactic drift, since it is used to obtain the
parallax of the group in question. When the sum
of the radial velocities of all the stars in the
group is formed the individual motions of the
stars cancel each other and the value remaining
represents the effect of the sun's motion on the
281

SPLENDORS OF THE SKY

group. The amount and direction of the sun's
motion is known and so the result gives directly the
parallax of the group.

Photometry, or the measurement of the apparent
brightness of the stars, is becoming more and more
important, since it has now become possible to
find the absolute magnitude or light-giving power
of stars of certain types independently of their
distances. When both the absolute and apparent
brightness of a star are known the star's distance
can be found, just as when we know the candle
power of a given light we can find the distance
at which it will have a certain apparent bright-
ness.

Absolute magnitude is the new unit for measur-
ing the light-giving power of suns, just as candle-
power is the unit for measuring the light-giving
power of terrestrial lights. It is defined as the
apparent brightness a star would possess if it
were at a distance of thirty-three light years from
the earth, which is the distance that corresponds
to a parallax of one-tenth of a second of arc. At
this distance the sun, which has the value minus
26.7 on the apparent brightness scale, has the
value 5 in absolute magnitude. That is, if the
282

SPLENDORS OF THE SKY

sun were thirty-three light years distant it would
appear to be only a fifth magnitude star.

The same scale of relative brightness holds for
the absolute magnitudes of stars as for the ap-
parent magnitudes, each unit of magnitude rep-
resenting a change in intensity in the ratio of
1 to 21/2- A change of five magnitudes means a
change of a hundred fold in brightness. A star
whose absolute magnitude is ten has only one-
hundredth of the light-giving power of the sun,
but if the absolute magnitude is zero the star is
a hundred times brighter than the sun. An ab-
solute magnitude of minus five means the object is
10,000 times more brilliant intrinsically than the
sun. It has been found that there is as great a
range in the actual or absolute magnitudes of the
stars as there is in their apparent magnitudes.

We come now to a most important point, upon
which depends the value of the photometric method
of finding the distances of star clusters thousands
and even hundreds of thousands of light years
distant. That is, there appears to be an upper
limit to the light-giving power of suns, and, more-
over, certain types of stars possess a nearly uniform
luminosity, the various stars of the type differing
283

SPLENDORS OF THE SKY

little among themselves in light-giving power. The
brilliant helium stars are all massive stars averag-
ing one hundred times brighter than the sun. The
giant red stars are still more luminous. The
Cepheid variables, valuable because the periods
of their light variations depend on their luminosity
so closely that their absolute magnitudes can be de-
termined when their periods are known, are also
giant stars. The Cepheids with periods less than
a day average one hundred times brighter than the
sun, while those of longest period are rarely sur-
passed in brightness by other stars.

These facts furnish a simple accurate method
for finding the distances of the globular star
clusters whose brightest stars are helium stars,
giant red stars and Cepheid variables. Measuring
the apparent brightness of the stars in various
clusters and knowing the absolute magnitudes of
these same stars, the distances of the globular
clusters can be found more quickly and easily than
the parallax of a star a hundred or so light years
from the earth can be found by the triangulation
method and with less error. The average absolute
magnitudes for the various types appearing in
clusters were obtained originally by the proper
284

SPLENDORS OF THE SKY

motion or parallactic drift method, using stars of
these types comparatively near.

It has been found by this simple method that
the globular clusters are the most distant celestial
objects known, except possibly the spiral nebulae.
The only limit set for the measurement of the dis-
tances of those objects lies in the limit of visi-
bility of the telescope used. There appears, how-
ever, to be a thinning out of these objects beyond
a distance of 200,000 light years, and it is possible
that all the globular clusters in the visible universe
are within the reach of telescopes now in use. The
60-inch Mount Wilson reflector shows stars down
to the twentieth apparent magnitude. The most
distant globular cluster, which represents the
greatest distance man has so far measured, is
200,000 light years distant and its brightest stars
are of the seventeenth apparent magnitude. A
margin of apparent brightness still remains for the
measurement of clusters still more distant if they
exist.

285

CHAPTER XXXVI

LAYING STARS IN THE BALANCES

weighing of the heavenly bodies, the sun,
the planets and the stars, appears a stupen-
dous problem, beyond solution, and so in truth it
was until Newton discovered that the law of gravi-
tation is universal and reaches even to the stars.

The same force that holds us to the earth holds
the earth in its orbit and sways the components
of a double star system. Every particle of matter
in the universe attracts every other particle with
a force proportional to the product of the masses
and inversely proportional to the square of the
distance between them. The greater the masses
and the less the distance between them the stronger
their attraction for each other. It is upon this
principle that the weighing of celestial as well as
terrestrial objects rests.

286

SPLENDORS OF THE SKY

If an object were not subject to the attraction
of neighboring masses it would travel forever in
a straight line. It is the attraction of nearby
objects that causes the path to deviate from a
straight line, and the amount of the deviation is
a measure of the attractive force of the disturbing
body.

In travelling eighteen and a half miles in its
orbit, the distance passed over in one second, the
earth falls about one-ninth of an inch from a
straight line in the direction of the sun, and this
is a measure of the sun's attraction for the earth.

The earth's attraction for an object at its sur-
face has been determined from observation, and
since it is also equal to the earth's mass divided by
the square of its radius it is possible to find the
mass of the earth in terms of some known mass at
its surface.

This has been done a number of times, but the
experiment is a very delicate and troublesome one,
since the attraction between bodies at the earth's
surface is so small that it is measured with great
difficulty.

A large metal ball or a mountain of known
mass is usually chosen, and its attraction for some

287

SPLENDORS OF THE SKY

object near by at a measured distance is deter-
mined observationally. This attraction is propor-
tional, according to the law of gravitation, to the
mass of the body, which is known in this case,
divided by the square of its distance from the
object attracted.

Comparing this attraction of one known mass for
another on the earth's surface with the attraction
of the earth for objects at its surface the ratio of
the earth's mass to the known mass is obtained. It
has been found in this way that the earth's weight
is about five and a half times that of an equal
volume of water.

This also gives the earth's density, which is
simply its mass divided by its volume, the standard
of comparison being the density of water.

Since the total weight of the earth averages
much more than the weight of the earth's crust
it is evident that the material near the earth's
centre is much more compressed and heavier than
at its surface, due to the tremendous pressure of
the overlying strata of the earth.

Knowing the weight of the earth and its distance
from the sun, we are in a position to find the sun 's
mass in terms of the earth's mass. It follows from
288

SPLENDORS OF THE SKY

the law of gravitation that the mass of a body
with a satellite is proportional to the cube of the
distance of the satellite divided by the square of
the satellite's period of revolution.

This will apply to the planet 's revolution around
the sun and that of the moon around the earth.
So if we find the cube of the earth's distance from
the sun and divide it by the square of the earth's
period of revolution, three hundred and sixty-
five and a quarter days, we have a number that
is proportional to the mass of the sun.

It comes out that this number is about three
hundred and thirty thousand times larger than
the number proportional to the earth's mass found
by dividing the cube of the moon's distance from
the earth by the square of its period of revolution
around the earth, so it is concluded that the mass
of the sun is three hundred and thirty thousand
times as great as the mass of the earth.

To find its density compared with the earth's
density we simply divide its mass compared with
the earth's by its volume compared with the earth's
volume, and we find that has only one-quarter of
the density of the earth or about one and a half
times the density of water. The sun therefore

289

SPLENDORS OF THE SKY

weighs only one and a half times as much as an
equal bulk of water would weigh.

Just as we have found the numbers proportional
to the earth's mass and the sun's mass so we can
find the numbers proportional to the masses of all
the other planets attended by satellites simply by
dividing, as before, the cube of the distance of the
satellite from the planet by the square of its period
of revolution around the planet.

Both of these quantities, the distances and
periods, can be determined from observations of
the satellites. Comparing, then, the values for
each planet with the number proportional to the
sun's mass, the mass of every planet that has
satellites is found in terms of the sun's mass and
also of the earth's mass. The mass of Jupiter and
also of Saturn has been found with great accuracy,
as both of these planets have a large number of
satellites.

Mercury and Venus, on the other hand, are the
most difficult to weigh, for they have no satellites.
Their masses have been found by observing their
attractions for comets and near-by planets which
produce "perturbations" in the motions and posi-
tions of the attracted bodies. These perturbations
290

SPLENDORS OF THE SKY

are, according to the law of gravitation, propor-
tional to the masses of the two bodies and inversely
proportional to the square of the distance between
the bodies affected.

The most difficult body to deal with in the solar
system is the moon. The problem of two attracting
bodies is easily solved mathematically, or even three
bodies if one of them is comparatively very small
or very remote, but in the case of the moon we
have a satellite that is very large compared to its
primary.

As a result there is a problem of three attract-
ing bodies, the sun, the earth and the moon, to
consider. The laws controlling the motions of
three bodies are as infallible as in the case of two
bodies, but the changes in the relative motions and
distances of the three bodies are so complex that
it lies beyond the power of mathematics to solve
the problem completely, and only approximations
to the complete solution are possible.

One method for obtaining the mass of the moon
is to compare the tide-raising force of the sun
with the tide-raising force of the moon. Another
is to measure the apparent displacement of the
sun in the heavens at half moon due to the fact
291

SPLENDORS OF THE SKY

that it is the centre of gravity of the earth and
moon that revolves around the sun under the laws
of gravitation and not the centre of the earth.

This centre of gravity lies, it has been found,
within the earth's surface and 2,880 miles from
its centre, and it follows as a result of this that
the earth's mass must be eighty-one and a half
times the moon's mass.

Knowing the relative masses of the members of
our own solar system, how can we find the masses
of the stars ? In the case of single stars this cannot
be done. All the stars are apparently moving
through space in straight lines. Up to the present
time no curvature in the paths of isolated stars has
ever been observed. If we were able to trace back
the orbits of the stars for some hundreds of thou-
sands of years we might make some interesting dis-
coveries concerning stellar motions; but so far as
we know now the stars are travelling in streams
or groups along parallel lines to and fro under
the general attraction of the entire system of the
stars, no star appreciably deflecting the motion
of any other.

There are, however, many stars that are not
single but consist of two or three, rarely more,
292

SPLENDORS OF THE SKY

components revolving around a common centre of
gravity. These are known as binary or multiple
stars, either visual or spectroscopic, and it is pos-
sible to determine their combined mass in terms
of the sun's mass provided the distance of the
binary star from us is known.

This is done in the same way that we compute
the mass of a planet that has a satellite. The dis-
tance of the companion star from its primary star
is found by observation, also the period that the
satellite requires to make a revolution around the
primary star. Then by the same law of gravita-
tion the cube of the distance of the satellite divided
by the square of its period gives the combined
mass of the star system in terms of the sun 's mass.

In case the centre of gravity of the system can
be found observationally the comparative masses
of the two stars become known also. Only the
masses of the nearest stars can be determined,
since the distance of the star system from the earth
is needed to solve the problem. The masses of
about ten or twelve stars have been determined by
this method, and though it is rather unsafe to
generalize from such a small number of stars the
results seem to indicate, what there is reason to
293

SPLENDORS OF THE SKY

suspect from other investigations of a different
nature, that the masses of the stars average about
the same as the mass of our own sun.

To weigh the heavenly bodies is not a simple
matter. Many observations and computations are
necessary. Since the discovery of the universality
of the law of gravitation astronomers have been
working on the problem and improving results, and
they are not yet at the point where they are satis-
fied with their results in spite of the fact that the
error in the value of the sun's mass is less than
one per cent, of the value given. The task of im-
proving the values of the masses and positions of
the heavenly bodies falls upon the theoretical
astronomer and is usually undertaken by the
National observatories or under special grants to
individuals fitted to cope with this arduous
problem.

294

CHAPTER XXXVIII

WONDERS OF OEION

ORION, the most magnificent of all the con-
stellations, is visible throughout the greater
part of the night in winter. The three bright stars,
evenly spaced in a straight line, that mark the
warrior's belt and the four brilliant stars in the
form of a huge quadrilateral that outline his body
are the most distinctive stars of the constellation.
They are among the first stars to shine forth after
sunset, appearing higher and higher in the eastern
sky on each successive evening.

In addition to forming the most impressively
beautiful of all the constellations, the stars of
Orion, with the exception of Betelgeuse, the deep
red star that marks the giant's right shoulder, all
belong to a connected system of inconceivably great
extent associated with one vast enveloping nebula.
295

SPLENDORS OF THE SKY

The denser portion of this nebula is known as the
" Great Nebula in Orion/7 considered by many to
be the most beautiful telescopic object in the
heavens. It covers a square degree in the sky and
is associated with the central star in the " sword
of Orion, ' ' which is formed by a row of faint stars
extending in a southerly direction below the belt.

In the midst of the great nebula glows an ex-
quisite little trapezium of stars, two of which are
attended by extremely faint companions. It is
known as the sextuple star, Theta Orionis. Not
far away, connected with the central nebula by a
faint nebulous extension, is the triple star Iota
Orionis, and the entire constellation abounds in
double and multiple stars, many of which are sur-
rounded by nebulous haze.

It is well known that the helium stars, the type
to which the Orion stars belong, are not univer-
sally distributed in space. They favor certain
regions and occur in loosely formed groups or
clusters, usually attended by nebulosity. They are
the most massive and the hottest of all the stars,
and they are never to be found far from the plane
of the Milky Way.

Prof. W. H. Pickering has made recent investi-
296

SPLENDORS OF THE SKY

Cations of the distance of the great Orion nebula,
and the size and luminosity of the Orion stars.
According to his results, this glorious constellation
is constructed on a plan of inconceivable grandeur.
The distance of the great Orion nebula he has
found to be a little over sixteen hundred light
years, corresponding to a parallax of ".002. If
we desired to express this distance in miles
Ave would have to multiply sixteen hundred by
Hie value of one light year in miles, or 63,000
limes the distance from the earth to the sun, re-
membering that the distance from the earth to the
sun is 93,000,000 miles. According to this same
estimate the luminosity of the brilliant blue-white
star Rigel, the brightest star in the constellation,
is nearly ninety thousand times that of our own
sun, while the triple star Iota Orionis mentioned
above is fifteen thousand times more luminous than
our sun.

Another estimate of the distance of the Orion
nebula made recently by Kapteyn places it at a
distance of six hundred light years, corresponding
to a parallax of ".0054, and gives the light-
'^iVing power of Rigel as nearly twelve thou-
sand times that of the sun and the light-giving
297

SPLENDORS OF THE SKY

power of Iota as two thousand times that of the
sun. If Prof. Pickering's estimate gives approxi-
mately the true distance of this wonderful con-
stellation then its brightest star Rigel is a super
giant among the stars, unsurpassed in brilliancy
by any other star unless we make an exception of
giant Canopus, the magnificent star of the South-
ern Hemisphere.

Astronomers have long held the theory that the
helium stars associated with the great irregular
nebulae, such as the stars of Orion and the Pleiades,
are being condensed from the nebulae with which
they are associated. The order of evolution has
always been assumed to be from nebula to star. In
light of more recent knowledge the idea is grad-
ually and persistently growing that in some in-
stances the evolution may be progressing toward
the nebula instead of away from it. In other
words, the nebulosity surrounding the Pleiades and
many of the stars of Orion may have been thrown
off from the surfaces of these stars. In the solar
corona and the zodiacal light and the tails of
comets, it has been suggested, we may see in a
slight degree the laws that govern the repulsion
of matter, under light pressure and possibly elec-
298

SPLENDORS OF THE SKY

tro-magnetic forces, at work in our own solar
system.

The characteristics of the novae or temporary
stars also give support to this view. Novae have
been seen to change from helium type stars to
bright line stars and then to planetary nebulae,
exactly reversing the accepted order of develop-
ment.

In his discussion of the great nebula and helium
stars in Orion Prof. Pickering says: "It was
formerly universally supposed that the nebulae
iv^ere condensing, but ... an appearance some-
what similar to the nebula was produced by photo-
graphing an explosion of flash powder." C. D.
Perrine, writing in the Astro-physical Journal,
Fays: "The dark, finely divided matter which is
believed to exist in the distant galactic regions
may be none other than condensed nebulosity; in
place of the early Orion stars, for example, being
wholly in the process of condensing from their
inclosing nebulous envelope, this nebulosity is, in
fact, largely the result of a great catastrophe, the
nebulosity having been thrown off in the process."
He asks : "Is this also true of the nebulosity in the
Pleiades with the difference that in the Pleiades
299

SPLENDORS OF THE SKY

the stars are slightly * older' in type and the nebu-
losity not self-luminous ? Has this nebulosity
frozen from a gaseous state?"

It is possible, according to Perrine, that the
Orion or helium type stars are extremely massive
and hot and confined to certain regions as a result
of varying external conditions existing in different
parts of the universe. Where cosmic matter is
dense stars of great mass and high temperature
would be found. The energy obtained from the
material gradually swept up by these stars would
exceed the energy lost by radiation. Their mass
and temperature would increase while light
pressure and electro-magnetic forces would drive
from these stars the lighter gases that form the
nebulosity enveloping them.

In parts of the universe where the cosmic matter,
either meteoric or gaseous, is less plentiful, the
evolution of the stars would be, on the contrary,
away from the nebula and toward the later and
cooler type stars, culminating in extinct, dark stars
following after the dwarf red type stars in
evolution.

300

CHAPTER XXXIX

THE CONSTELLATIONS OF WINTER

A MONG the sparkling brilliants of midwinter
•* *• skies are three, Betelgeuse in Orion, Sirius in
Canis Major, the Greater Dog, and Procyon in
Canis Minor, the Lesser Dog, that outline in the
heavens a huge equilateral triangle that is as con-
spicuous a figure in the winter as the Great Square
in Pesagus is in early fall.

During the early evening hours of February this
massive triangle of first magnitude stars will be
found not far from the meridian, the two Dog Stars
following closely at the heels of the warrior Orion
as with uplifted club he pursues Taurus, the Bull,
across the heavens to the westward.

Ruddy Betelgeuse is in the right shoulder of
Orion, and not far away to the west glows Alde-
baran, the brightest star in the V-shaped group of
301

SPLENDORS OF THE 'SKY

the Hyades, also deeply red, representing the bale-
ful light in the eye of the Bull as he charges with
lowered head at the warrior Orion.

At no other season is there presented so finely to
view such an impressive assemblage of first magni-
tude stars. Eight of the twenty brightest stars in
the heavens are now visible in our latitudes in the
early evening.

If we are south of the thirtieth parallel we may
also see Canopus of the Southern Hemisphere, sec-
ond only to Sirius in apparent brightness, the star
of immeasurable distance and unimaginable size
and splendor that in actual luminosity makes Sir-
ius appear but a dwarf. Ten thousand times the
light-giving power of the sun is the lowest limit
that can be set for the light-giving power of this
supergiant, and it may far exceed this amount.

Sirius, at the southeastern vertex of the tri-
angle, is one of our nearest neighbors in space, and
is only surpassed in brightness by the planets Jup-
iter and Venus and occasionally Mars. Its light
takes between eight and nine years to reach our
solar system, however, and its distance, if we wish
to express it in miles, amounts to about 550,000
times the distance from the earth to the sun.
302

SPLENDORS OF THE SKY

Sirius is attended by a companion that is one of
the most feebly luminous bodies known. Though
its mass is about one-half that of Sirius, it would
take 20,000 such companions to equal Sirius in
brightness. The two stars are separated from each
other by a distance of 1,800,000,000 miles, which is
the same as the distance of the planet Uranus from
the sun. Though the light of the two stars com-
bined is forty-eight times that of our own sun,
their combined mass is only between three and
four times the sun's mass, so low is their density.
Procyon, at the northeastern vertex of the triangle,
is another neighbor of the solar system, being only
ten light years distant. It also is attended by a
companion star.

The two combined radiate about six times as
much light as our own sun, but are only one and
one-third times more massive. Were our own sun
as far from us as Procyon it would appear to be
only one-sixth as bright as this first magnitude star.
Euddy Betelgeuse, the third star in the triangle,
presents a strong contrast to the other two in every
way.

It is in the first place so distant that it gives no
measurable parallax. In comparison to Betel-
303

SPLENDORS OF THE SKY

geuse, Sirius and Procyon are dwarfs. Like Rigel
and Canopus, Betel geuse is one of the supergiants
of the universe. Though one of the stars in Orion
it is not physically associated with the great con-
stellation and its enveloping nebulosity. It is trav-
elling in a different direction and simply chances
to lie in such a position as to complete the quad-
rangle that roughly outlines the form of the war-
rior.

Betelgeuse is not only far more distant and
far more luminous than Sirius and Procyon,
but also radically different in its physical con-
dition.

These three stars represent three distinctive
types and three widely different stages of evolu-
tion. Sirius is a star of the hydrogen type, which
is, in fact, sometimes referred to as the Sirian type
after this illustrious member. Next to the helium
stars, of which nearby Rigel, the brightest star in
Orion, is an example, these hydrogen stars are the
hottest of all the stars.

Their brilliant surfaces are not veiled by cooler
enveloping layers of metallic vapors such as sur-
round the photosphere of our own sun and stars
still more advanced in type. Intense absorption
304

SPLENDORS OF THE SKY

lines of hydrogen in the spectrum give them their
characteristic name and prove that they are sur-
rounded by glowing hydrogen gas.

The intense blue-white and white light of the
helium and hydrogen stars respectively is an in-
dication of their great heat, for the hotter a body
the more intense are its radiations in the violet and
ultra violet end of the spectrum.

As a body cools the maximum intensity of its
radiations shifts toward the red end of the spec-
trum.

Fully half of all the stars so far examined have
proved to be either helium or hydrogen stars. This
may be due to the fact that these intensely brilliant
stars may be seen to a far greater distance than
less luminous stars.

Procyon stands between the hydrogen and solar
stars in type, and more closely approaches our
own sun in its physical condition. Strong lines
of calcium are one of the most distinctive features
of the spectra of such stars, though the hydrogen
lines are still very conspicuous, as they are also in
the spectrum of our own sun.

Stars such as Procyon are usually spoken of as
calcium stars, owing to the prominence of the lines
305

SPLENDORS OF THE SKY

of this element in their spectra. Other metallic
lines also begin to appear faintly at this stage of
evolution and such stars are slightly tinged with
yellow as their atmospheres become charged with
the vapors of the denser gases.

Compared to Sirius, Procyon is noticeably yel-
lowish and this tinge is still further deepened in
the solar stars to which our own sun belongs. Bril-
liant Capella, also visible at this time, due north of
Betelgeuse and midway between it and the pole, is
a typical solar type star in which the metallic lines
so faint in Procyon have increased in strength
until they equal the hydrogen lines in intensity.
Such stars are decidedly cooler than the hydrogen
and helium stars and the more deeply they are
tinged with yellow the more are their atmospheres
charged with the heavier metallic vapors.

A still later stage in the evolution of the stars is
typified in the orange-colored star Aldebaran in
the Hyades just to the northwest of Orion. In
stars of this class the metallic lines have increased
in strength until they have become stronger than
the lines of hydrogen. The rays from the blue end
of the spectrum have become absorbed more and
more in an increasingly dense atmosphere and for
306

SPLENDORS OF THE SKY

this reason such stars are reddish orange in ap-
pearance.

We now arrive after all these gradual changes
at the type of the giant red star Betelgeuse that is
so radically different from the types of the two
stars Sirius and Procyon. Betelgeuse is an irregu-
larly variable red star.

The majority of stars of this class are variable
in their radiations for some reason not clearly un-
derstood. Any one observing this interesting red
star from season to season will readily note its pe-
culiar fluctuations of brightness.

At times it is only a shade brighter than Alde-
baran, a convenient star with which to compare it.
Again it will be equal in brightness to Rigel,
diagonally opposite to it in the quadrilateral of
stars.

The spectrum of Betelgeuse is that of a typical
giant "M" star, as it is called astronomically. It
is beautifully fluted in appearance, due to the pres-
ence of the compound known as titanium oxide.
The presence of oxides in the atmosphere of a star
indicates a decided drop of temperature, for no
such compounds could exist unless the temperature
were comparatively low. Why titanium oxide
307

SPLENDORS OF THE SKY

should so completely dominate the spectra of such
stars is one of the unsolved mysteries of the stars.
It is also one of the compounds that appear in the
spectra of the sun spots. The temperature of sun
spots, it is well known, is decidedly below that of
the surrounding solar surface. Only a few hundred
stars of the same type as Betelgeuse are known and
they are all believed to be at great distances and
at least several thousand times more luminous than
our own sun.

The cause of the irregular fluctuations of bright-
ness of these stars is believed to lie within the
stars themselves. No law or order in its workings
can be detected as yet, however. Betelgeuse usually
goes through its irregular variations of light, which
amount to about half a magnitude at most, within
a year or two.

There is, at the greatest, a change of more than
forty per cent, in the intensity of the radiations
of this star. Its sudden and unexpected increases
of luminosity may possibly occur when its dense
atmosphere of metallic vapors is temporarily
rent by the pressure of pent-up forces within
a highly heated interior. To live upon planets
encircling such suns would appear to us extremely
308

SPLENDORS OF THE SKY

hazardous and no more to be relished than exist-
ence near an active volcano.

An outburst of activity that would rapidly
change the intensity of the radiations of such a
star nearly fifty per cent, would have a most dis-
astrous effect upon organisms with which we are
familiar. And yet adaptations to conditions under
the sway of such an erratic ruler might be such
that the life process would continue there no more
disturbed than it is on our own planet when pass-
ing clouds temporarily conceal the face of the
sun.

309

CHAPTER XL

THE CONSTELLATIONS OP SPRING

TT IS not difficult to locate all the constellations
*• for a certain season of the year if we once fix in
our minds the positions of two or three of the
more prominent groups. Let us consider first the
two constellations known as Ursa Major, "The
Great Bear, ' ' and Leo, ' ' The Lion. ' ' Both are con-
spicuous in the spring, and we should have no
trouble in locating them readily.

At nine o'clock on the first of April these two
groups are almost directly on the meridian. A
month later they, as well as all the other constel-
lations, have apparently shifted about thirty de-
grees westward. The winter constellations have
disappeared below the western horizon and the con-
stellations that are overhead in summer evenings
are now appearing on the eastern horizon. Taking
310

SPLENDORS OF THE SKY

as our time of observation May first, about nine
o'clock in the evening, we find in the north, just
west of the meridian, the seven stars of the Big
Dipper, or Great Bear, and south of it Leo facing
westward.

The head of Leo is outlined by a sickle-shaped
group of stars, six in all, with the bright, white star
Regulus in the end of the handle. To the eastward
we see the other stars that outline the body. Dene-
bola, a star of the second magnitude, marks the
tail and is about twenty-five degrees east of Regu-
lus. With these reference points we can easily lo-
cate other conspicuous constellations. Southeast
of Leo is Virgo, a large Y-shaped constellation,
which contains the beautiful white star Spica, and
again southeast from Virgo is the small constella-
tion Libra, marked by four rather faint stars. To
the southwest of Spica is a more conspicuous group
of stars of the second and third magnitude in the
form of a quadrilateral. This is the constellation
Corvus, and just west of Corvus is the less conspic-
uous group known as Crater. In the southern skies
we also have the long constellation of Hydra, which
extends from a point a little southwest of Regulus,
where a small group of faint stars mark the head,
311

SPLENDORS OF THE SKY

to a point in the southeast, where the fiery Antares
will soon rise in the constellation Scorpio. Hydra
contains one second magnitude star known as Al-
phard or Cor Hydrae, standing very much alone.
It is about twenty degrees south of Regulus and a
little to the westward. This long, but rather faint
constellation of Hydra extends nearly ninety de-
grees across the southern sky below Leo, Virgo,
Crater, Corvus and Libra. Let us return now to
the Great Bear, which, by the way, is a much more
extensive constellation than the part which forms
the Big Dipper, or the tail and body of Ursa Major.
A considerable portion of the space south and east
of the configuration known as the Big Dipper be-
longs to Ursa Major. It is occupied, however, by
inconspicuous stars. On a line between the ena
star in the handle of the Dipper and Denebola in
Leo are situated two very interesting, though small,
constellations; Canes Venatici, the more northerly
one, is marked by two stars, the Hunting Dogs,
with which Bootes the Herdsman is chasing the
Great Bear around the pole. The northern of the
two dogs is Asterion, the southern Chara. Be-
tween Denebola and Canes Venatici is the constel-
lation, almost directly overhead at this time, known
312

SPLENDORS OF THE SKY

as Coma Berenices. In this constellation, it is esti-
mated, over a hundred nebulae are gathered in
a space no greater than that covered by the full
moon. This little constellation also contains a
great number of fifth and sixth magnitude stars
and many interesting doubles. Canes Venat-
ici also contains some fine doubles and a beautiful
star cluster, as well as the noted " Whirlpool Neb-
ula." Both constellations offer a fine field for the
telescope.

If we now turn to the western sky we can
trace out a bright arc of first and second mag-
nitude stars beginning with Capella, the yel-
lowish star in the northwest in the constella-
tion Auriga. We can distinguish Capella also
by the group of three stars about five degrees
to the southwest, known as the "Kids." Fol-
lowing this arc from Capella southward we come
first to Beta Aurigae, then in order, Castor and
Pollux in Gemini and finally Procyon in Canis
Minor.

In the east we now see the large constellation

of Hercules. Hercules contains no star of the first

or second magnitude, but many of the third. It

contains one of the finest star clusters in the heav-

313

SPLENDORS OF THE SKY

ens, seen on a clear, dark night as a patch of
white light. The telescope dissolves it into a
magnificent cluster of over 5,000 stars. Northeast
of Virgo and southeast of Ursa Major is the large
constellation of Bootes, a kite-shaped configuration
of stars whose principal star is the ruddy Arcturus.
Almost overhead now is the conspicuous equilateral
triangle formed by the three bright stars, Dene-
bola in Leo, Spica in Virgo and Arcturus in Bootes.
Once located in the heavens it will never be forgot-
ten, and when we see it high in the heavens in the
evening we know that spring has come once more,
for it is known as the characteristic configuration
of spring. Between Hercules and Bootes is the
Northern Cross, a beautiful little semicircle of six
small stars. It was in this constellation that the
"blaze star," or Nova, of 1866 appeared. In the
northeast is the small constellation of Lyra, iden-
tified at once by the brilliant blue- white star Vega.
Directly east of Vega is the constellation Cygnus,
known as the Northern Cross, now coming into
view low in the northeast.

Bootes, Corona Borealis, Hercules, Lyra and Cyg-
nus are all in a line across the heavens and Arc-

314

SPLENDORS OF THE SKY

turus, in Bootes, Alphacca, the brightest star in
Corona; Vega in Lyra and Deneb in Cygnus are
on a diagonal line directed toward the north-
east.

315

CHAPTER XLI

THE CONSTELLATIONS OF SUMMER

THE constellations that are most noticeable
during the summer months are Scorpio in the
south, Hercules and Corona Borealis directly over-
head at nine o'clock the middle of July and Ophiu-
chus and Serpens between these two constellations
and Scorpio.

In the northwest can be seen the Big Dipper,
which never sets in our latitudes, but is best seen
in the spring and summer months. In the fall and
winter it appears to rest upon the horizon and is
too low to be well seen. The head of Draco is now
nearly on the meridian and just north of Hercu-
les. It is marked by a group of four fairly bright
stars, and from there the neck and body can be
traced first eastward, then curving northward and
bending sharply westward, so that the body lies
316

SPLENDORS OF THE SKY

between the creature's head and the Little Dipper,
and twines around between the two Dippers. The
tip of the tail lies at the middle of the line between
the Pointers and the Pole Star. The Pointers, we
remember, are the two stars farthest from the
handle of the Big Dipper that outline the outer
edge and a line drawn through them and extended
northward a distance about equal to the whole
length of the Big Dipper brings us to the Pole
Star, which is a second magnitude star at the end
of the handle of the Little Dipper.

The Northern Cross, in Cygnus, is now conspic-
uous in the northeast. The brightest star, Deneb,
or Arided, as it is better called, for there are sev-
eral Denebs in different constellations, is situated
at the northern end, or top, of the Cross and Albireo,
the noted double at the bottom. Arided, or Deneb,
lies in a line with Vega in Lyra, the next constella-
tion west of Cygnus, Alphacca in Corona and Arc-
turus in Bootes, which is now west of the meridian.

Spica, in Virgo, sparkles brilliantly, low in the
southwest. Vega still remains the most brilliant
star visible, although ruddy Arcturus is of the same
magnitude. We include in our list of bright
stars Antares in Scorpio, which is on the meridian
317

SPLENDORS OF THE SKY

well to the southward at this time, and Altair, in
Aquila, a yellow star of the first magnitude, which
is well up in the eastern sky. It is readily found
from the fact that it is attended by two fainter
stars exactly in line with it and at nearly equal
distances on either side. In the constellation of
Aquila, about twenty degrees southwest of Altair,
appeared the brilliant Nova of 1918, known as Nova
Aquilae No. 3, since it was the third Nova to ap-
pear in this constellation. About fifteen degrees
northeast of Aquila is the little diamond-shaped
group of third magnitude stars, known as Del-
phinus and often called " Job's coffin."

Vega, as well as Altair, is accompanied by two
fainter stars. They form a small equilateral tri-
angle with it, whose sides are only two and one-
half degrees long. A sahrp eye will detect the fact
that Epsilon Lyrae, the northernmost of the two
stars, is double, and a small telescope will show that
the star is really quadruple, each of the two com-
ponents of the wide double being also double. It is
the finest example we have of a quadruple star.
All four stars are physically connected and form
one mighty system. Beta Lyrse, which lies about
eight degrees southeast of Vega, is both a variable
318

SPLENDORS OF THE SKY

and double star. In the short period of thirteen
days its brightness fluctuates nearly a magnitude.
Its change in brightness is due to the fact that it
has a companion star that intercepts at times part
of the light from the brighter star.

It requires considerable stretch of imagination
to trace some of the mythical and legendary figures
that have been mapped out in the heavens. It is
rather difficult to see that Lyra is a harp or Her-
cules and Ophiuchus heroes performing wonder-
ful feats with serpents. Bootes is a hunter pur-
suing the Great Bear around the Pole, accompan-
ied by the two hounds, Canes Venatici, though ac-
cording to some legends he is represented as a
herdsman driving the seven plough oxen, the stars
that form the Big Dipper. The giant Hercules
stands with his foot on the head of Draco and his
body is marked by a quadrilateral of four stars
midway between Lyra and Corona Borealis, or the
Northern Crown. The latter constellation is one
of the few that really resembles the object for
which it is named, as it consists of a nearly perfect
semicircle of six stars. The brightest, Gamma or
Alphacca, is the gem in the crown.

Alpha Hercules, which marks the head of Eer-
319

SPLENDORS OF THE SKY

cules, is a variable star which changes irregularly
in brightness from the third to the fourth magni-
tude. It is also a beautiful orange and blue double.
One can easily find it in connection with Alpha
Ophiuchi, which is about six degrees east of it and
which forms with Vega and Altair a nearly equi-
lateral triangle. Alpha Hercules is the fainter of
the two stars. The large constellations of Ophiu-
chus and Serpens lie west of Aquila and south of
Hercules and Corona. The head of Serpens
lies about ten degrees south of Corona Borealis and
is marked by a group of small stars ; from there a
line of bright stars can be traced first to the south-
west for a few degrees, then south and eastward
almost to Aquila. Ophiuchus, the serpent bearer,
is another mythological figure represented by a con-
siderable number of fairly bright stars grouped in
rather indefinite forms. The hero is represented
with his feet on Scorpio and his head very close to
Hercules, while he grasps Serpens with both hands.
Scorpio is directly south of Ophiuchus. Fiery An-
tares marks the creature 's heart and his tail is a
long line of stars reaching nearly to the southern
horizon. The constellation is of peculiar shape and
easily recognized. The two bright stars in Libra,
320

SPLENDORS OF THE SKY

the next constellation westward, marked the crea-
ture's claws according to some ancient maps, but
there is considerable confusion as to the exact
boundary between the two constellations. Antares
is a most interesting object in the telescope, as it is
a double star with a small green companion. As
its name indicates it is the * ' Rival of Mars ' ' and to
the naked eye shows a strong resemblance to the
ruddy planet.

Sagittarius is now visible in the southeast,
its little inverted milk dipper outlined by five stars.
A little southwest of the star in the end of the
handle is a small triangle of stars, making a no-
ticeable group of eight stars in all. Sagittarius
and Scorpio mark one of the most interesting re-
gions of the sky, as the Milky Way is particularly
dense and bright here, and very peculiar in struc-
ture. According to the most recent researches it is
in this general direction that the center of the
sidereal universe is located.

321

CHAPTER XLII

THE CONSTELLATIONS OP AUTUMN

ACH season of the year brings its character-
istic configuration of stars in the heavens.
The magnificent constellation of Orion is always
associated with winter months. The great triangle
formed by Spica, Denebola and Arctums appears
in spring and early summer, while the Scorpion
with red Antares glowing in its heart is seen in
southern skies on midsummer nights. In Autumn
we have the Great Square in Pegasus, visible in the
east in September, overhead in October.

At nine o'clock the middle of September the
Northern Cross of the constellation Cygnus is di-
rectly in the zenith, while Altair in Aquila is just
west of the meridian. Altair can always be recog-
nized by the two fainter stars that are in line with
it at nearly equal distances on either side. Del-
322

SPLENDORS OF THE SKY

phimis, the Dolphin, is a little diamond-shaped
group of third magnitude stars commonly spoken
of as Job's Coffin, that now can be found on the
meridian south of Cygnus and about twenty de-
grees to the northeast of Altair. It contains a few
other faint stars visible to the naked eye, in addi-
tion to those that form the diamond. Vega in
Lyra is the most brilliant star visible and is just
west of the meridian.

In western skies the extensive constellation of
Hercules is still in view and south of it Ophiuchus
and Serpens. Bootes and Scorpio are now at the
western horizon and the Dipper is far over to the
northwest.

Turning to the eastern half of the heavens, we
cannot fail to discover the Great Square in Pe-
gasus. It is best considered in connection with
Andromeda, as the star in the northeast corner of
the square does not belong to the constellation
Pegasus, but is Alpha Andromedaa, one of the three
stars in a curved line that belong to the constel-
lation Andromeda, which is now in the northeast
just south of the peculiar W-shaped group of stars
that forms the constellation of Cassiopeia. An
imaginary line drawn from Polaris, the Pole Star,
323

SPLENDORS OF THE SKY

through the star in the W that is farthest west,
known as Beta Cassiopeiae, and extended as far
again, brings us to Alpha Andromedae in the corner
of the Great Square. About fifteen degrees due
west is Beta Pegasi, an irregularly variable star
that marks the northwestern corner of the square.
Near this star is a group of three fainter stars that
also belong to the constellation Pegasus. The star
that marks the southwestern corner is about fifteen
degrees due south of Beta Pegasi, and is known as
Markab. A line from Alpha Andromedae drawn
diagonally across the square to this star and ex-
tended as far again passes through the neck and
head of the Winged Horse. His hindquarters are
missing on star maps that show the mythological
figures, but his forelegs are marked by four faint
stars northwest of the square and just east of Cyg-
nus. About fifteen degrees due south of Alpha
Andromedae is the second magnitude star that com-
pletes the Great Square. The entire constellation
of Pegasus covers an extensive region in this por-
tion of the heavens.

The Great Nebula in Andromeda, visible even to
the naked eye, can be found about ten degrees
northwest of the middle star in the line of three
324

SPLENDORS OF THE SKY

stars that characterizes the constellation of Andro-
meda, It forms a little triangle with two faint
stars near it.

Just east of the meridian at this time and above
and west of the W-shaped group of stars in Cas-
siopeia is the constellation Cepheus, which con-
tains very few bright stars. The remarkable va-
riable star Delta Cephei, which changes more than
a magnitude in brightness in about five days, is
one of the stars in a little triangle that marks the
king's head. Cepheus is represented as sitting
behind his wife, Cassiopeia, with his feet on the
tail of the Little Bear. Andromeda, the daughter,
is represented with her head resting upon the
shoulder of Pegasus, the winged horse, that brought
Perseus to rescue her from Cetus, the sea monster,
lying far to the south beyond the constellations
Aries and Pisces. Perseus is the brilliant constel-
lation just east of Andromeda crossed by the Milky
Way.

The Milky Way is now a beautiful sight upon
clear nights. It passes from Cassiopeia across the
shoulder of Cepheus, through Cygnus in the zenith
and thence divides into two branches, one passing
through Aquila and Sagittarius, and the other
325

SPLENDORS OF THE SKY

through Ophinchus to Scorpio. Near this point
the two branches again meet.

Of the zodiacal constellations now visible Sagit-
tarius is readily found in the southwest by its
peculiar configuration of eight bright stars,
five in the shape of a little dipper inverted toward
the southern horizon and three forming a tri-
angle southwest from the star at the end of the
handle.

East of Sagittarius come in order the three
zodiacal constellations, Capricornus, Aquarius, and
Pisces. Capricornus, the sea goat, represented with
the head and body of a goat and tail of a fish, has
few bright stars. It contains, however, one of the
few double stars visible to the naked eye, Alpha
Capricorni.

A line drawn from Albireo at the bottom of the
northern cross through Altair and extended about
as far again, brings us to this double. Three
degrees further south is Beta Capricorni, the
brightest star in the constellation.

Aquarius, the water bearer, is east and north of
Capricornus and southwest of Pegasus. The char-
acteristic configuration of this constellation is the
little Y of third and fourth magnitude stars about
32G

SPLENDORS OF THE SKY

20 degrees southwest of the square in Pegasus.
This is supposed to represent the water jar from
which Aquarius pours the stream of water out-
lined by many faint stars lying to the southwest
and south. At the southern end of this stream is
Piscis Austrinus, the Southern Fish, which con-
tains one first magnitude star, Fomalhaut, just
visible above the southern horizon at this time of
year. It is in line with the western edge of the
•square in Pegasus, but fully 45 degrees south.
Directly south of the Great Square in Pegasus is a
little polygon of faint stars which marks the head
of one of the two fish in the zodiacal constellation
Pisces. A line of faint stars runs from here east-
ward to meet another line of stars extending in a
northerly direction toward the constellation And-
romeda. This second line of stars represents the
second fish in the constellation, and contains no
bright stars. Part of the large constellation of
Cetus, the Whale, is directly south of Pisces
and Beta Ceti, which stands entirely alone, is
the brightest star in this part of the heavens.
The Chaldeans called this region the Sea, and
it is not strange, for we have here Cetus, the
Whale, the two fish in Pisces and Pisces Aus-
327

SPLENDORS OF THE SKY

trinus, the Southern Fish, as well as Aquarius,
the Water Bearer, Capricornus, the Sea Goat, and
Delphinus, the Dolphin, quite an aquatic collec-
tion!

328

CHAPTEB XLIH

BRILLIANT STARS OF THE SOUTHERN HEMISPHERE

QTAR gazers of northern lands often overlook
^ the fact that some of the most brilliant and
beautiful stars and finest nebulae and star clusters
in the heavens belong to the southern hemisphere
a ad are not visible in our latitudes.

The brilliant first magnitude star Formalhaut
that culminates in the zenith in thirty degrees
south latitude comes about twenty degrees above
oar southern horizon in late summer and autumn
months to give us a hint of the beauties of the
southland, and if our view of the southern horizon
is not obstructed by houses, trees or mountains, as
in so often the case, we may then see this interest-
ing star of the south. Stars are never seen at their
best when near the horizon, however, for we then
view them through denser layeri of atmosphere
329

SPLENDORS OF THE SKY

than if they were nearer the zenith. All ce-
lestial bodies shine brightest when they are over-
head.

Magnificent blue-white Canopus, the second
brightest star in the heavens, lies just below our
southern horizon in the large and important south-
ern constellation of Argo Navis, named for the fa-
mous ship of the Argonauts. It is usually divided
into three constellations — Puppis, Carina and Vela.
Canopus was the chief pilot of the Argonauts, but
the star was known and worshipped on the banks
of the Nile long before it received its name from
the Greeks and it has been called the Star of Egypt.
It has also been a guide to many tribes in Africa,
South America and Australia in their journeys
through pathless wilds.

Although Sirius appears nearly twice as brilliant
as Canopus, this is due only to the fact that Sirius
is comparatively near to us, not quite nine light
years distant, while no accurate measurement of
the distance of Canopus has yet been made. It is,
as far as we know, the greatest of all the giant
suns and its light-giving power has been estimated
as high as fifty thousand times that of our own
sun. Sirius, with a brilliancy estimated at forty-
330

SPLENDORS OF THE SKY

eight times that of the sun, shrinks into a pygmy
when compared with Canopus.

Other brilliant first magnitude stars in southern
nkies that are invisible to us are Alpha Centauri,
the nearest of all the stars and one of the finest
doubles in the heavens ; Beta Centauri, a beautiful
white star near Alpha — the two reminding us of
the twins in Gemini; Achernar, far south in the
river Eridanus, and the beautiful bluish-white
double star, Alpha Crucis, the brightest of the four
stars that form the Southern Cross.

The constellation of the Southern Cross is the
most noted of all the southern constellations. It
nerves as a timepiece for the southern hemisphere,
;just as the Great Dipper does for northern lands.
It stands in a nearly upright position when cul-
minating or passing the meridian.

Early Spanish conquerors of Mexico and South
America regarded this cross as a token of heaven's
approval of their attempt to plant the Christian
faith in the wilds of the New World. Upon the
first maps of the southern hemisphere South Amer-
ica appeared as "Terre Sancte Crucis," the Land
of the Holy Cross.

The southern constellations Argo Navis, Crux
331

SPLENDORS OF THE SKY

and Centaurus, are all traversed by the Milky
Way.

The galaxy in Argo Navis is crossed by many
dark bars, and near the Southern Cross is the pe-
culiar pear-shaped hole known as the Coal Sack.
One of the most peculiar stars in the heavens is
situated in southern skies and is invisible in our
latitudes. This is Eta Argus, which lies in the
midst of a nebula and possesses most unusual and
irregular fluctuations of light which distinguish it
from various classes of variable stars or temporary
stars.

As far back as the year 1677 this star was ob-
served to fluctuate in brightness. Between that
date and 1800 records show a great range of bright-
ness. In 1843 it became brighter than any other
star except Sirius. At present it is barely visible
to the naked eye. When at its brightest, in 1843,
it gave 25,000 times the amount of light that it
does now.

Far to the south in the circumpolar constellation
Tucana is to be found the finest of all globular star
clusters and in Argo Navis there is the finest ir-
regular star cluster in the heavens. Two splendid
globular star clusters, located in this large and
332

SPLENDORS OF THE SKY

noted constellation, are visible even to the naked
<}ye. In Argo we also find the largest and brightest
of the naked eye nebulae.

Of unusual interest in the southern hemisphere
are the Lesser and Greater Magellanic Clouds.
They look very much like small star clouds de-
tached from the girdle of the galaxy which en-
eircles the heavens.

The Magellanie Clouds are rich in nebulae, va-
riable stars and star clusters and the Greater Cloud
has a decidedly spiral form. It has been suggested
that our own stellar system, with its millions of
stars, its galactic star clouds, its nebulae, variable
stars and star clusters would present very much
the same appearance that the Greater Magellanic
Cloud does to us if it were transported to a dis-
tance of a hundred thousand light years.

Those who travel to the southern hemisphere are
impressed by the fact that no bright star marks
the south pole of the heavens. To locate the north
pole we have the bright second magnitude star,
Polaris, at the end of the handle of the Little Dip-
per, and the two stars that outline the front of the
bowl of the Big Dipper act as pointers to the pole
atar.

333

SPLENDORS OF THE SKY

The seven stars of the Big Dipper are familiar
to nearly every one in northern latitudes. As we
pass southward the pole star sinks lower and lower
toward the northern horizon, for its altitude above
the horizon always equals the latitude of the ob-
server. At the equator the north pole lies in the
horizon, as does also the south pole. The belt of
Orion crosses the meridian in the zenith. The view
of the heavens from the tropics is probably unsur-
passed, for we see from here the finest constella-
tions of both hemispheres.

As we pass into the Southern Hemisphere the
Big Dipper gradually sinks below the northern
horizon and we turn our eyes toward the unfamiliar
constellations surrounding the south pole, which
rises higher and higher in the sky as we go south-
ward. Canopus in Argo Navis, brilliant Achernar
and the four stars of the Southern Cross now
mount high into the heavens and the dearth of
bright stars in the neighborhood of the south pole
is very evident.

We miss the familiar Dippers of northern lands

encircling the north pole of the heavens and find it

hard to accustom ourselves to circumpolar regions

so different. Toward the northern horizon we now

334

SPLENDORS OF THE SKY

see the familiar star groups that passed through
our zenith in middle northern latitudes, the North-
ern Cross, Lyra, and the Northern Crown, Bootes,
Hercules, Perseus Andromeda and Pegasus usher-
ing in the different seasons.

335

CHAPTER XLIV

THE ONE-HUNDRED INCH TELESCOPE OF THE MT.
WILSON OBSERVATORY

>TpHE 100-inch mirror for the greatest reflecting
-•• telescope in the world arrived safely at the
summit of Mount Wilson, Cal., 5,700 feet above
sea level, in July, 1917.

The new reflector has a light gathering power
three times as great as that of the five-foot reflector
of the Mt. Wilson Observatory, which shows stars
as faint as the twentieth magnitude. It will, there-
fore, show stars one magnitude fainter.

It is estimated that fully one hundred million
additional faint stars are within reach of this great
reflector. Some of these stars may be comparatively
near to us, their feeble luminosity being due to the
fact that they are dwarf suns ; others may be faint
only because they lie on the outskirts of the uni-
336

SPLENDORS OF THE SKY

verse. In actual luminosity such stars would equal
or surpass our own sun.

Next to the 100-inch reflector in size comes the
72-inch reflector of the Dominion Astrophysical
Observatory which started on its observing career
in the spring of 1918. The greatest refractor is
the 40-inch telescope of the Yerkes Observatory.
Reflecting and refracting telescopes differ radically
in their treatment of the light received from the
stars. In a refractor the rays of light pass through
the lens at the upper end of the telescope tube
and travel down the tube, coming to a focus at a
point within. They are then examined by the ob-
server by means of the eye-piece at the lower end of
the telescope tube. In the reflecting type of tele-
scope the mirror is placed at the lower end of the
tube and reflects the incident ray back through the
tube to a secondary mirror placed so as to receive it
before it reaches a focus and to reflect it in turn to
the observer or photographic plate placed at one
side.

It is possible to make reflectors much larger
than refractors, since it is not essential that
the glass be absolutely pure. In a reflecting tele-
scope the function of the mirror is merely to act
337

SPLENDORS OF THE SKY

as a support for a thin silver coating which is
deposited upon its upper concaved surface. Twice
a year this silver coating must be renewed.
Arrangements have been made to have this quickly
and easily done in case of the new reflector. The
mirror will be removed by means of an electric
elevator to the resilvering room in the same build-
ing. Since light does not penetrate the mirror, but
is reflected from its highly polished surface to a
secondary mirror and thence to the photographic
plate or eye of the observer, it is not necessary that
the glass entering into its composition have the
high degree of perfection essential to the lens of a
refracting telescope. The reflector is unsurpassed
for photographic or spectroscopic work inasmuch
as the quality of the light received is unchanged.
In a refracting telescope the rays are always to
some extent broken by passage through the lens.
Perfect achromatism is the strongest point in favor
of the reflector.

The field of good definition for the great reflector
is small, however, only equalling in area one-half
the disk of the moon. This is a restriction placed
by the necessity for rapid photographic action.

Work upon the great reflector began in 1906,
338

SPLENDORS OF THE SKY

when the St. Gobain glass works in France under-
took to manufacture a block of glass large enough
and perfect enough for a telescope of this size.
After many attempts covering an interval of three
years a satisfactory piece of glass for the great
mirror was finally obtained and delivered at the
optical shops of the Mount Wilson Observatory in
Pasadena, Cal., twelve miles from the summit of
Mount Wilson.

Here for seven years it was to undergo a long
process of grinding, polishing and figuring. All
of this work was done by Prof. George Ritchey, a
member of the staff of the observatory. In its fin-
ished condition the mirror weighs four and a half
tons and is nearly thirteen inches in thickness.
This thickness is essential to prevent the mirror
bending of its own weight. It has been subjected
to many tests, increasing in refinement as the work
progressed, and is now considered to be practically
perfect.

On July 1, 1917, it was packed in an octagonal
shaped box lined with paraffin to keep out the dust
and taken up the narrow winding mountain road
six miles in length on a truck geared to a maximum
speed of two miles an hour. Another truck pre-
339

SPLENDORS OF THE SKY

ceded it, also a gang of workmen with tools to re-
pair any defect in the road. The great sections of
the casting were made at the Fore River Shipyards
at Quincy, Mass., and shipped around Cape Horn,
because they were refused as shipments by rail-
roads, being too wide for flat cars and too high
for tunnels. All parts of the great instrument that
were not of unusual size and that required careful
workmanship were designed and made at the in-
strument shops of the observatory in Pasadena.

The instrument is housed in a steel building with
a 100-foot dome weighing 500 tons that revolves
easily and rapidly by means of electrical ap-
pliances. The moving parts of the great reflector,
which weigh about 100 tons, are also electrically
controlled. Every detail upon which the success-
ful operation of the huge instrument depends has
been carefully worked out by opticians and instru-
ment makers connected with the observatory.

The problems that the new instrument will assist
in solving will be chiefly of an astrophysical nature
in keeping with the lines of research undertaken by
this observatory, such as the form and extent of
the universe, the nature of star clusters and neb-
, the origin and evolution of stars and their
340

SPLENDORS OF THE SKY

physical properties, streaming tendencies and ve-
locities. Most of all this work will be done by
means of photographic and spectroscopic attach-
ments and not by direct observations.

At the present time special attention is being
given to the red stars as bearing upon the question
of the scattering of light in space. It has been ob-
served that among stars fainter than the eighteenth
magnitude there are few, if any, whiter than our
own sun, which is classed as a yellow star, although
faint white stars are present in the star clouds of
the Milky Way.

This preponderance of red stars among the
faint stars, which are on the whole the most dis-
tant, has led to the belief that minute particles of
matter, cosmic dust, may scatter the light of dis-
tant stars and give them a red tinge, just as the
rays of the setting sun have a reddish tinge due
to their passage through the dense, low-lying strata
of the atmosphere. It is known, on the other
hand, that stars also acquire a reddish tinge with
advancing age and a lower temperature, and also
that as a star advances in age its velocity increases,
and so the question arises whether these faint stars
may not be reddish because they are advanced in

341

SPLENDORS OF THE SKY

type, and distant, because they have travelled far.
It is one of the questions that the new instrument is
well qualified to attack, since it is particularly
adapted to a study of faint, distant stars.

It is also peculiarly fitted to investigate the mys-
terious spiral nebulas, especially the smaller mem-
bers of the class. Are they " island universes,"
faint because of great distance, or do they repre-
sent the first stages in the birth of star systems
comparatively near and small? There are spirals
of all degrees and magnitudes, from the Great
Spiral in Andromeda, visible to the naked eye, to
the faintest specks of spiral form visible in the
large telescopes. What will the great reflectors
have to tell of these wonderful formations?

The feelings of the explorer must come to those
first privileged to guide this mighty instrument
and penetrate into regions of space hitherto unex-
plored. Man stands upon his tiny planet, which
is but an atom in the universe, and tries to extend
his vision further and further into the eternity cf
life that flows in a ceaseless cycle of change before
his eyes. Very slowly and laboriously and heavily
handicapped he tries to solve, step by step, the
mighty riddle of creation.
342

SPLENDORS OF THE SKY

One more step forward will be taken when this
noble instrument is turned toward the heavens and
those who have labored long and tirelessly to make
it worthy of its task begin to gather the precious
fruits of their labors.

343

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