LITTLE BLUE BOOK NO. 895
Edited by E. Haldeman-Julius
Astronomy for
Beginners
Hereward Carrington, Ph.D.
Author of the following Little Blue Books: No.
679, “Chemistry for Beginners;” No. 491, “Psychology
for Beginners;” No. 419, “Life: Its
Origin and Nature;” No. 524, “Death and
Its Problems;” No. 493, “New Discoveries
in Science;” No. 409, “Great
Men of Science;” etc., etc....
HALDEMAN-JULIUS COMPANY
GIRARD, KANSAS
Copyright, 1925,
Haldeman-Julius Company
PRINTED IN THE UNITED STATES OF AMERICA
CONTENTS.
Page
Introductory 5
Astrology 7
The Solar System 8
The Sun 9
Mercury 11
Venus 12
The Earth 13
Mars 13
Jupiter 16
Saturn 17
Uranus 18
Neptune 18
The Minor Planets 19
Are There Other Planets? 20
The Moon 20
The Origin of the Solar System 24
Constellations 27
Meteors: “Shooting Stars” 28
Meteorites 29
Comets 30
Nebulae 32
The Milky Way 33
The Number of Stars 33
The Position of Our Solar System 35
The Movement of Our Solar System 36
Distances of the Stars 36
Temperature of the Stars 37
Fixed Stars 37
Double Stars 38
Colored Stars 38
Variable Stars 39
Temporary Stars 40
Star Groups--Clusters 40
Eclipses 41
Telescopes 43
The Spectroscope: Spectrum Analysis 43
Photography 46
The Tides 47
Gravitation 48
The Ether 49
Atomic Analogies 49
Thunder and Lightning 50
Fireballs 50
Atmospheric Electricity 50
The Earth’s Magnetism 51
The Aurora Borealis 51
Time: Measurement of 52
Space: Measurement of 52
The International Day Line 54
Calendars, etc. 54
Curved Space 55
The Temperature of Space 55
Light in Space 55
Life in Space 56
The Causes of an Ice Age 56
Why Do Stars “Twinkle”? 56
Why Does the Moon Sometimes Appear Larger? 57
Are the Planets Inhabited? 57
A Few Definitions 58
INTRODUCTORY
Astronomy is one of the oldest of the sciences--as it is one of the
most fascinating! The early Egyptians, Assyrians, Babylonians and
Chaldeans were, as we know, great astronomers, and, considering that
they were compelled to make their observations without the aid of
telescopes, some of their conclusions are truly remarkable in their
accuracy. Men must always have gazed at the stars, and wondered at
their number and their beauty; yet it is only within the past three or
four centuries that accurate ideas as to the nature, size and structure
of our Universe have come into being. No subject is so calculated to
impress upon man his own relative insignificance as astronomy--to show
him that the speck of matter upon which he dwells is so small that it
cannot even be seen, from a relatively short distance in space! How
puny and absurdly trifling seem his bickerings and his disputes, his
wars and his hates, his jealousies and his failures, when viewed from
the standpoint of infinite time and infinite space; mere struggles
upon an ant hill, which, a few million years from now, will be
uninhabitable, while the sublime immensity of Nature will proceed as if
nothing had happened!
Yes, astronomy is a fascinating and romantic study, and the following
little book is an attempt to summarize, very briefly, the most
important findings of modern astronomical science upon this question.
I have endeavored to make the subject as simple as possible, and to
avoid all terms of a technical character, unless these are fully
explained. It is my hope that the reader may be enabled to gain a
fairly clear and accurate idea as to the nature and constitution of our
Universe by a perusal of this little book.
ASTRONOMY FOR BEGINNERS
ASTROLOGY
Those who have not studied this subject will often ask the question:
“What is the difference between Astronomy and Astrology?” It is merely
this: Astronomy studies the heavenly bodies, and their movements, etc.,
by all available scientific means; while astrology, also utilizing
this material, further asserts that the particular relative positions
which the sun, moon, planets and other heavenly bodies occupy at the
moment of birth _influence the individual_ born at that moment, and
continue to influence him all through life. In other words, astrology
is undoubtedly an exact science in so far as its astronomical _data_
are concerned; but its further inference, as applied to the living
human being, is not; it depends upon historic beliefs and traditions
which have been handed-down for centuries. So far as astronomers have
been enabled to ascertain, there is not the slightest scientific basis
for any belief in astrology; assuredly it is a curious and interesting
occult study, but it must be understood to lie within that realm,
rather than in that of exact astronomical science.
THE SOLAR SYSTEM
When we speak of the “solar system,” we mean our central Sun, and the
various planets which revolve around it. The planets, beginning with
the one nearest the Sun, and proceeding outwards into space, are:
Mercury, Venus, The Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Most
of these planets have in turn, circling round them, smaller bodies
of satellites; the Earth has but one--the Moon. Other planets have
more than one. The planets vary greatly in size, as well as in their
relative distances from the Sun. The following may help the reader to
form a mental picture of their relative distances and sizes:
Imagine a large open common; on it place a globe 2 feet in diameter,
by way of representing the Sun; Mercury will then be represented by a
mustard seed at a distance of 82 feet; Venus by a pea at a distance of
142 feet; the Earth also by a pea, at a distance of 215 feet; Mars will
be a small pepper corn, at a distance of 327 feet; the Minor Planets
by grains of sand at distances varying from 500 to 600 feet; then a
moderate sized orange ¼ of a mile distant from the central point will
represent Jupiter; a small orange ⅖ths of a mile, Saturn; a full-sized
cherry, ¾ths of a mile, Uranus; and lastly a plum, at 1¼ miles,
Neptune,--the most distant planet yet known,--though some astronomers
suspect there may exist another planet still further off, and hope one
day to find it. (On the same scale, the _nearest_ “fixed” star would be
7,500 miles distant).
THE SUN
The Sun is the center of our solar (sun) system; it is the great giver
of light and heat, without which life upon our planet would soon become
extinct. It is an immense body, more than a million times the size
of our earth. In fact, its _radius_ is nearly twice the distance of
the moon from the earth! The mass of the Sun is 332,000 times that of
the earth. It gives 600,000 times as much light as the full moon. The
energy radiated per square yard from the Sun is equivalent to 140,000
horse power. The heat radiated by the sun would melt a layer of ice
4,000 feet thick every hour, all over its surface. Various estimates
of the amount of heat upon the surface have been made, but these do
not agree,--figures all the way from 10,000° F. to 180,000° F. having
been given. Certain it is that its internal heat is terrific, and there
is every indication that this heat has been more or less constant for
millions of years in the past. No purely physical theories of its heat
are at all satisfactory. The ultimate nature and source of the sun’s
heat are unknown--though various theories have been advanced by way of
explanation. I have discussed this question at some length, however in
my little book in the present series, “New Discoveries in Science,” to
which the reader is referred. (“What Keeps the Sun Hot?”)
The nature and constitution of the sun have, of course, been studied
intensively for many years by astronomers. The apparent surface of the
sun is called the “photosphere” (light surface). It is the part that
gives forth most of the light and heat. Above the photosphere lies
a sheet of gas, probably from 500 to 1,000 miles thick, called the
“reversing layer,” which is cooler than the photosphere. Outside the
photosphere is another layer of gas, from 5,000 to 10,000 miles deep,
called the “chromosphere” (cooler sphere). The outermost portion of the
Sun is the “corona” (crown). It is a halo of pearly light surrounding
the sun, but it cannot be seen except during a total eclipse. It is of
irregular form, and gradually fades out into the blackness of space
at a distance of from 1,000,000 to 3,000,000 miles. This must not be
confounded with the so-called “prominences,” which are vast eruptions
of flame, spurting out from the sun’s surface, and extending into space
for enormous distances--perhaps half a million miles! These also travel
with enormous velocity--five or six hundred miles per second. The earth
would appear an insignificant speck of dust, in this vast, roaring
furnace of flame!
Of late years, the question of the so-called “sun spots” has aroused
a great deal of interest, partly by reason of the fact that they
apparently affect electrical and magnetic conditions upon the earth.
These “spots” seem to reappear at stated intervals, and about every
eleven years reach their maximum intensity, (The period of the
revolution of the sun on its own axis has been estimated by their
study.)
Although the sun-spots were studied before the eighteenth century,
it is only within the past few years that the significance of these
enormous spots has become known. For long it was thought that they were
merely the great volcanoes of the sun; centers of great heat, generated
by the glowing, fiery gases of the sun. In 1908, however, Prof. Hale
demonstrated that the sun-spots acted as attraction centers, which drew
towards them the hydrogen of the solar atmosphere. “Subsequently, it
was found that these spots are the seats of great cyclones, in which
cool hydrogen gas is set whirling and is sucked down in the great
mælstrom of the Sun, rushing into the center of the spot at the rate of
60 miles a second. Consequently the spots are the center of great solar
disturbances, which are of an electromagnetic nature.” From this it was
concluded (1) that the spots are cooler than the surrounding area; (2)
they are centers of violent cyclones; and (3) they are magnetic fields
of great intensity. The connection of sun-spots with our weather, and
the relation of one to the other, have also been studied within the
past few years.
MERCURY
This is the smallest of the planets in our solar system, being only
about 3,000 miles in diameter. It revolves round the sun in almost
exactly 88 days, at a distance of approximately 36,000,000 miles,
varying between 28½ million to 43½ million miles. Owing to its
smallness, it is often difficult to see this planet, and a powerful
telescope must be employed to study it effectually. It is thought
that Mercury possesses mountains, but it is practically devoid of
atmosphere. Dark, irregular spots have been observed upon the planet,
and its surface is thought, by some astronomers, to resemble that of
Mars, to a great extent. The solar heat on Mercury is about seven
times that on us, owing to its proximity to the Sun. Schiaparelli,
and others, have contended that the period of rotation of Mercury is
exactly equal to its period of revolution round the Sun. If that be
true, one side of the planet is always turned to the Sun, and the other
side away from it. One side of the planet would thus be intensely hot,
while the other side would be icy cold. Comparatively little is known
concerning this small planet, though much study has been devoted to it.
VENUS
This is one of the brightest and most beautiful “stars” in the sky,
and has for long been the theme of poets. It is practically the same
size as our earth, its diameter being approximately 7,500 miles. It
travels round the Sun in 224 days, at a mean distance of 67,000,000
miles. It revolves on its own axis in about 23½ hours, so that its days
are nearly the same as ours. It is thought that Venus has a fairly
dense atmosphere, and also water-vapor, which proves the existence
of water upon its surface. Dense layers of cloud exist in the upper
regions of its atmosphere, making direct observations of its surface
very difficult. For this reason, comparatively little is known as to
the conditions on the surface of Venus. Every eighth year Venus passes
through a period of great brilliance, being then so bright as to cast
a shadow, like the Moon. Venus must have a higher temperature than
our earth; its sky is always overcast; thunder and lightning must be
never-ending. Some controversy has existed as to the habitability of
Venus; but the consensus of opinion is that life would be practically
impossible upon its surface.
THE EARTH
The earth on which we dwell was thought by the ancients to be the
center of the entire Universe--the Sun, stars and the vast host of
Heaven were thought to revolve around it. This was the so-called
“geocentric” theory. It was later on displaced by the so-called
“heliocentric” theory, when it was found that the Sun, and not the
Earth, was the center of our system. It only remains to be said
that our Earth is the third of the planets which revolve round the
Sun--Mercury and Venus being nearer the Sun than we are, and the others
still further removed in space. We are thus but one of a number of
similar bodies moving through space, all revolving round the central
Sun.
MARS
This now-famous planet is somewhat smaller than our earth, being about
5,000 miles in diameter. It travels round the Sun in 686 days, at a
mean distance of 140,000,000 miles. The eccentricity of its orbit is
considerable. Mars appears to us reddish in color, owing to the vast
stretches of arid soil (desert) which exist upon its surface. Water
exists, but it is relatively scarce; it is gradually drying-up, as it
does in the case of all bodies of the kind--the water on our own earth
is very gradually becoming less and less, as the centuries pass.
Mars has been drawn particularly to the public’s attention, of late
years, by reason of the dispute (still raging) as to its habitability,
and the character of its so-called “canals”--the more or less regular
markings, like long, dark lines which have been seen to exist upon its
surface. Its surface has accordingly been studied minutely for many
years, but it may be said that no unanimity of opinion exists as to its
being an inhabited planet. Says Kæmpffert, in his “Astronomy,” (pp.
183-84):
“The mapping of Mars is no recent matter, for even in 1659 a rough
sketch of the surface of the planet was made by Huygens, in which
the V-shaped markings at the equator, pointing to the north, can be
identified as the _Syrtis Major_. This was followed by rough sketches
from time to time down to 1840, when Maedler first began a systematic
charting of the planet. His map was followed in 1864 by Kaiser’s, by
Flammarion’s in 1876, and Greene’s in 1877. Drawings of various parts
of the planet were made during these intervals, but were not combined
into good charts.”
“Observations made by Prof. Lowell and his staff at the Observatory,
at Flagstaff, Arizona, have had a study of this planet especially in
view.... The surface of Mars as seen in the telescope, is composed of
two white polar caps, which wane with the approach of summer; orange
areas, which are supposed by Lowell to be deserts, and blue-green
areas, which change their hue to orange during the Martian autumn and
winter, and resume their verdant tint in spring. The planet is covered
with a network of fine lines, first discovered by Schiaparelli, in
1877; and called by him ‘canals’--a designation by which they are still
known. These canals connect the polar caps with the temperate and
equatorial zones. According to Prof. Lowell, they may be regarded as
planetary irrigation ditches, which serve the purpose of leading the
melting water of the poles to those desert regions which would still
blossom, if properly watered. The canals disappear with the approach of
winter, and creep down from the poles towards the equator in summer--a
phenomenon which long puzzled astronomers, until Pickering ingeniously
suggested that we see, not the canals themselves (for they are much too
narrow) but the vegetation which fringes their banks--which withers as
the cold of winter descends, and which flourishes with the melting of
the snows.”
It may be said that this theory of the canals on Mars is not
universally accepted by astronomers, but is warmly disputed in some
quarters. The _markings_ are undoubted; but some astronomers are
inclined to think they are due solely to vegetal growth, and are not
the result of human hands. The controversy still continues. Meanwhile,
two satellites of Mars were discovered in 1877.
JUPITER
Jupiter is the largest of all the planets, having a diameter of about
88,000 miles; it is only about 1,000 times smaller than the sun--that
is, about 1,000 times larger than our earth. In volume, it is 1,300
times larger than our globe. Gravitation must be enormous on its
surface. Its density is however relatively low--being only about
one-quarter that of the earth. It is thought to be a world of water and
more or less dense gas. It is constantly covered by a thick blanket
of clouds and vapors, making direct observation very difficult--as we
saw was the case with some other planets. Immense as this planet is
in size, it revolves at a tremendous speed--approximately 10 hours.
Owing to its immense bulk, it cools more slowly than a body such as our
earth. Consequently it will take tens of millions of years for it to
cool sufficiently to permit life to become manifest upon its surface.
Yet it may at that time! In a sense, Jupiter may be said to be a planet
of the future; when our earth is cold and dead, Jupiter may be teeming
with animate existence.
Jupiter has 8 satellites, and a number of dark bands cross its surface
from east to west. A certain dark spot upon its surface has caused
great interest among astronomers, who are unable to determine its exact
nature. This planet revolves round the Sun in rather more than 11¾
years, at a mean distance of 483,000,000 miles.
SATURN
Saturn revolves round the Sun in 29½ years, at a mean distance of
886,000,000 miles, in an orbit slightly eccentric. According to
Barnard, its equatorial diameter is 76,470 miles, and its polar
diameter 69,770, which figures imply a polar compression of 1/11. This
planet is famous for the celebrated “ring” which surrounds it. As a
matter-of-fact, when observed by means of high-powered telescopes, this
famous “ring” is found to consist of a number of rings--three being
clearly distinguishable. For long it was thought that these rings were
vaporous; then that they were solid; but the present view is that they
are composed of myriads of discrete particles of matter, so closely
compacted together that to our remote eyes they appear as a solid mass.
These rings are fairly broad, but relatively thin in diameter; they
resemble a sort of huge disk. Perhaps 100 miles would be the thickness
of these rings. Their diameter, however, is tens of thousands of miles
in breadth. Owing to these rings, Saturn is one of the most beautiful
of all the planets, when viewed through a high-powered telescope.
Saturn doubtless has certain features in common with Jupiter, as to its
physical appearance. The general hue of the planet is yellowish-white;
it probably has no atmosphere, or at most a very tenuous one. It is
attended by ten satellites, the largest of which is known as Titan,
thought to be about 2,700 miles in diameter.
URANUS
This is the next to the last planet in our solar system. It is a large
planet, having a diameter of about 31,000 miles. Uranus revolves
round the Sun in rather more than 84 years, at a mean distance of
1,781,000,000 miles. It is attended by four (or five) satellites. Belts
and spots have been seen upon its surface, but relatively little is
known concerning its physical conditions, owing to its great distance
from us, and its relative smallness. This planet was discovered, as
is well known, by Herschel, and was named after him, but its name was
subsequently changed. (It is still mentioned as Herschel, in certain
books upon Astrology.) It is probable that the temperature of Uranus
is relatively low, owing to the small percentage of the sun’s rays
which reach its surface. It has been calculated that its theoretical
temperature is about 330° F.
NEPTUNE
The past century was remarkable for the discovery of this new planet:
Neptune. How it was accomplished is a matter of great interest. In
1820, it was found that Uranus was not following its computed path.
Adams, of Cambridge, and Leverrier, of Paris, each independently took
up this question, and, assuming that this perturbation was due to the
presence of a planet still more remote from the sun (which had been
hinted at in 1830 by Bessel) they set to work to calculate its position
in the heavens. They finished this at about the same time, arriving at
practically the same conclusions. Adams’ results were first submitted
to the Astronomer Royal, who set them aside without consideration until
too late. Leverrier sent his conclusions to a German astronomer, Galle,
who found the planet the first evening he looked for it, September 23,
1846.
Neptune is the furthest known planet of our solar system; it is a very
large body, having a diameter of about 37,000 miles. It revolves round
the sun in an immense orbit which it takes 164 years to complete. Its
mean distance from the Sun is nearly 2,800,000,000 miles--a majestic
sweep through the heavens! Relatively little is known as to the
physical conditions of Neptune, owing to its immense distance, and its
relatively small size. At least one satellite is known to exist. The
temperature on Neptune must be extremely low, owing to its distance
from the sun, whose rays would be exceedingly feeble at that great
distance.
THE MINOR PLANETS
Between Mars and Jupiter, a number of small bodies are known to exist,
which have sometimes been dignified by the name of “minor planets.”
They have also been called “Planetoids” and “Asteroids.” Special names
have been given these individual small bodies--Eros, Ceres, Pallas,
Vesta, Juno, etc. Eros passes, upon occasions, very close to our
earth; again passing beyond the orbit of Mars. Several hundreds of
these smaller planets are now known to exist--as though they were the
remnants of some shattered world. These bodies are very small: Ceres,
_e.g._, being about 250 miles in diameter; Pallas, 304 miles; Vesta,
211 miles; while a number of the others are thought to be from 5 to 15
miles in diameter.
ARE THERE OTHER PLANETS?
Inasmuch as some of the planets known to us have only been discovered
so lately (relatively) the question has naturally been asked: “Why may
there not be _other_ planets, beyond Neptune, still undiscovered?” It
is a perfectly legitimate question, and no definite answer to this
query can be given. It seems rather improbable that another planet
will be discovered. However, it is a conceivable possibility, and M.
Flammarion has stated that, in his estimation, such a planet probably
exists--gravitating at a distance 48 times as great as the distance
between the earth and the sun--that is to say, 7,500 million miles, in
an immense orbit which it takes at least 330 years to accomplish. Proof
as to the existence of such a planet has not, however, as yet been
forthcoming.
THE MOON
The Moon is the Earth’s only satellite, and by far the nearest body in
space to our Earth. Many astronomers are inclined to think that the
Moon at one time formed a part of the Earth, but was wrenched away from
it, leaving a huge cavity, which is now occupied by the Pacific Ocean.
The Moon is a cold body, emitting no light or heat of its own; all the
light which it seems to shed is entirely _reflected_ light--reflecting
the sun’s rays, much as a mirror might reflect them; hence its
beautiful silver color.
In round numbers, the Moon is approximately 240,000 miles distant
from us in space--the distance varying from 221,600 miles to 252,970
miles--causing a corresponding variation in its apparent diameter and
parallax.[A] The circumference of the Moon’s orbit is a little more
than a million-and-a-half miles, and it travels through space with the
velocity of 2,288.6 miles per hour, or 3,357 feet per second.
[Footnote A: See page 58 for a definition of this term.]
Our satellite always keeps the same face turned towards the Earth, so
that we only see one side of it; the other side is forever hidden from
the sight of man. However, the axis of the Moon tilts, in relation to
the earth, and permits us to glimpse a little more of the surface both
north and south, so that about five-eighths of the surface has actually
been observed.
The surface of the Moon has been subjected to intensive study, and its
“geography” is now as well known as that of our own earth. Vast “seas”
(i. e.) sea bottoms, mountain ranges, solitary mountain peaks, enormous
craters, are readily observed, and modern telescopes have now brought
the moon so close to us that it has been said that any body as high as
the Woolworth Building, in New York, would cast a shadow which could be
observed and noted.
The fact that the same face of the Moon is always seen by man does not
mean that this body remains stationary; it revolves on its own axis,
from west to east, but this revolution occupies exactly one siderial
month. The result is that the days and nights on the Moon, are many
times the length of our days and nights. The surface exposed to the
sun’s rays must get extremely hot, and, when deprived of these rays,
extremely cold. It has been estimated that the mean temperature of the
moon’s surface must approximate 200° F., during the “day” time, and
approach the intense cold of inter-stellar space during the “night”
(perhaps -250° C.). This would render life or vegetation of any kind
very unlikely. However, Professor Pickering has lately asserted that
vegetation _does_ apparently spring into being with extreme rapidity
during the moon’s day time--evidently remaining latent during the
intense cold of the “night.” (Some interesting material on this topic
may be found in Shipley’s “Is the Moon a Dead World?” No. 557 of the
present series.)
The volume of the Moon is about one-fiftieth that of the earth, but
its mass is only about one-eightieth that of our planet. The Moon
is practically devoid of atmosphere, which is another reason why it
cannot support “life,” in our sense of the word. Two theories have
been advanced as to the absence of the moon’s atmosphere: (1) that it
gradually combined, chemically, with the materials on its surface;
and (2) that it gradually escaped into space, because of the low
gravitational pull of the moon. There is no water on our satellite,
which means that there is no ice and no snow. The moon being so much
smaller than our earth, the pull of gravity is of course much less also.
Yet it is well known that the tides, on the earth, are greatly
influenced by the moon. Every atom composing our satellite must exert
some subtle pull upon every atom of our oceans, in order thus to affect
them. What is the nature of this attraction? Here we encounter the
mystery of gravitation! This question must accordingly be postponed
until we come to our discussion of that subject.
One of the most remarkable and distinguishing characteristics of the
moon consists in the so-called “lunar craters,” which appear to be
immense, extinct volcanoes. More than 30,000 of these have now been
mapped, varying in size from small hills to immense basins 50, 60, 100
miles in diameter. Ptolemy is 115 miles across, while Theophilus is 64
miles in diameter and 19,000 feet deep. The curious thing about these
lunar craters is that they are unlike the hilly volcanoes known to us
on our earth. They are rather huge circular pits, often square miles in
extent, surrounded by a circular wall, and almost invariably having a
single mountainous cone in the center.
Various theories have been advanced by way of explanation of these
craters. The most important of these are (1) that they represent
extinct volcanoes; (2) that they indicate spots where masses of matter
have dashed into the moon, from surrounding space; and (3) that
they represent the surface of the moon, when it was a hot, seething
mass--their resemblance to the “bubbles” formed at the surface of
boiling glue, mud, etc., being pointed to as analogous. Unanimity of
view does not exist even yet as to their origin.
The ever-changing “phases” of the moon have been observed by
generations of lovers. Thus, the new moon, full moon, etc., are
commonplace sights. These apparent changes are, of course, due entirely
to the relative position of the sun at the time. If the sun illumines
the whole face of the moon, as viewed from our earth, we have full
moon; if only a small portion of it, we see the first quarter, etc.
The whole disk of the moon may always be seen, however, by careful
observation. It is hardly necessary to say that the so-called “Man in
the Moon” is a mind’s eye picture, created by the configuration of the
various mountains, seas, etc., upon its surface.
THE ORIGIN OF THE SOLAR SYSTEM
Men in every age have speculated as to the constitution and origin
of our world, and of the Universe in general. The first really
detailed and scientific attempt was made, however, little more than a
hundred years ago by Laplace--and subsequently known as the Laplacian
hypothesis (1796).
Concurrent with the establishment of new facts, there was a tendency,
throughout the past century, to find some philosophic interpretation
of the Universe and its structure; to ascertain, if possible, the
“beginnings of things,” and explain them in some satisfactory manner.
This has been considered as epoch-making in astronomical research as
Darwin’s great theory of the Origin of Species was in biology. The
history of the two theories has been similar also. Both have served a
useful purpose; have helped to direct scientific thought for years; and
both are now largely outgrown. Both were, however, of great value and
of daring originality.
Laplace assumed the primal existence of a glowing ball of gas rapidly
revolving about an imaginary axis running through its center of
gravity. During the process of cooling, this mass would contract, and a
disk of gas would be thrown off in this manner; and hence a number of
gaseous rings be formed, which would ultimately cool down and assume a
spherical form. Laplace conceived that this process might be interfered
with by internal accident and by comets from without.
The first modifications of the theory were suggested by Sir Norman
Lockyer, who proposed what is known as the meteoritic hypothesis in
its place. The central idea of the theory was that--“All self-luminous
bodies in celestial space are composed either of swarms of meteorites
or of masses of meteoric vapor produced by heat.” The theory was based
on spectroscopic analysis. It said that the original nebulæ were
composed, not of gases, but of meteoric material and cosmic dust. This
theory was never fully accepted in place of that of Laplace, however;
but it paved the way for a more recent theory, which may be said to
be satisfactory and more or less inclusive. This is known as _the
planetesimal hypothesis_, and was advanced within the past few years
by F. R. Moulton and T. C. Chamberlin, of the University of Chicago.
At the present time, it may be said to be the accepted theory, so far
as any such theories are accepted, since it accords with all the facts
in a remarkable manner, and has been experimentally demonstrated. In
outline, the theory is as follows.
If examination of the nebulæ in the sky be made, out of 120,000 of
them, nearly every one of them is found to be in the spiral form.
So common and universal is this, indeed, that it was concluded that
this must represent “some prevalent process in celestial dynamics.”
This process is, according to Chamberlin, the actual formation of a
solar system. As this spiral revolves, it accretes to itself various
smaller bodies, with their gases, atmospheres, etc., and these become
consolidated with the original body. As time went on, this spiral
gradually tended to decrease its speed, but at the same time, continued
to accrete bodies which came into contact with it in its flight
through space. Thus, we have to imagine our world, not as an expanded
molten mass which has continuously cooled and contracted, but, on the
contrary, as a small lump of cold and solid fragments that, moving
about in accordance with its attractions, continuously fed upon its
surrounding assemblage of “smaller fry,” and thus grew to its present
size. About the young earth so engaged it is possible to read, on the
basis of the hypothesis, something of its early history.
Thus we see that the old theory of Laplace has been reversed; and that,
instead of a great central mass of moving, white-hot gas, we have a
number of smaller bodies, all busily engaged in building up themselves,
at the expense of the surrounding masses of still smaller matter--much
as a crystal accretes to itself minute specks of crystalline matter
from the solution in which it is immersed. This is the newest of the
cosmological theories. According to it, all the planets might have been
formed at the same time. This view of the formation of the universe
opens up still wider problems, which are now the subject of keen debate.
CONSTELLATIONS
The ancients, when studying the heavens, saw all kinds of imaginary
animals in the various star-groups, and named them accordingly. A
constellation is really a group of stars, which seems to constitute a
sort of system of its own. Thus, we find reference to the Great Bear,
the Little Bear, the Bull, etc. It is difficult for the uninitiated
to see the resemblances which the ancients did, in these various
star-groups, and astronomical science has re-named them, as well as
adding a large number of new constellations to those already known.
Stars of the first six magnitudes (roughly) are visible to the
unaided eye; those of lesser magnitude must be detected by the aid
of telescopes. About 5,000 are thus visible; the number is increased
according to the magnifying power of the telescope used, and it is
estimated that there are more than 100,000,000 within the range of
visual and photographic instruments!
The names of a few of the best known constellations are as follows:
Ursa Major (The Great Bear); Cassiopeia; Hercules; Scorpio (the
Scorpion); Corona Borealis (The Northern Crown); Boötes (The Hunter);
Leo (the Lion); Andromeda; Perseus; Auriga (The Charioteer); Taurus
(the Bull); Orion; Canis Major (The Great Dog); Canis Minor (The
Smaller Dog); Gemini (the Twins), etc.
In these various constellations, certain noted stars are to be found.
Thus, in Gemini, its two principal stars are Castor and Pollux. In
Canis Major is Sirius. In Orion may be found Aldebaran and Betelgeuse.
The Pleiades and Hyades groups are in Taurus. In Perseus is Algol. In
Lyra is the first-magnitude star Vega. And so on.
The “Big Dipper,” so-called, is part of the Constellation Ursa Major;
and it is almost universally known that the Pole Star (Polaris) may
readily be found by its means. The constellations must be traced and
learned, one by one; but this the student must accomplish for himself!
METEORS: “SHOOTING STARS”
What are popularly known as “shooting stars” are not stars at all; they
are really meteors which appear at altitudes of from 60 to 100 miles,
as a rule, from the earth, and move over paths of 40 or 50 miles at a
rate of from 10 to 50 miles per second.
The light given out by meteors is due to their being heated by friction
with the atmosphere. Falling from space, they become attracted by the
earth’s gravitation, and fall towards it. Here they encounter the
earth’s atmosphere, and their rapid passage through it creates terrific
heat, which tends to consume them before they reach the face of the
earth, turning them into gases, or causing them to fall gently as dust.
This sudden flash is the “shooting star” in question.
The number of such meteors is very great. It has been computed that
between ten and twenty million strike the earth’s atmosphere daily.
Occasionally, a large number of meteors fall together; and then we have
a “meteoric shower.”
METEORITES
Occasionally, however, some of these bodies _do_ reach our earth,
despite the friction and opposition of the earth’s atmosphere. Such
bodies are called meteorites, siderites, or aerolites. Only a few of
these are seen to strike the earth yearly, and it is a remarkable fact
that, so far as we have any record, not one of them has ever struck a
town or killed an individual. The outside of the meteorite during its
passage through the air is subject to intense and sudden heating, and
the rapid expansion of its surface-layers often breaks it into many
fragments. The surface is fused and, on striking, cools rapidly. The
result is that it has a black, glossy structure, usually with many
small pits where the less refractive material has been melted out. Such
meteorites may be seen in most large museums.
COMETS
During the past century, many of these “tramps of the solar system”
have been discovered and their orbits computed. The “head” may range
from ten thousand to a million miles, or more, while its “tail” may
stream across the heavens for millions of miles. These comets’ tails
always point away from the sun; and for long the reason for this was
not known. It is now believed that this is due to light-pressure; the
energy of the sun’s rays press this delicate matter outwards into
space. (This theory has been elaborated at considerable length by the
Swedish astronomer and chemist, Arrhenius.)
Many readers of this little book will remember the excitement caused
by Halley’s comet, which came relatively close to the earth in 1910,
so that many persons thought there would be a collision, and were
terrified accordingly! As a matter of fact, the tails of comets are
usually of almost inconceivable tenuosity. Halley first observed this
comet, computed its orbit and predicted the date of its return.
Some comets have tails: others do not. Not much is known concerning
the origin and destination of comets; where they originated, or how.
They travel at tremendous speed over many millions of miles of space,
returning after a few years, or after a lapse of several centuries.
They are very striking looking, even when observed by the naked eye. A
number of comets have been noted. The following are a few of the more
remarkable comets which were observed during the past century:
The Comet of 1811. This was visible for nearly a year and a half, and
was carefully studied by William Herschel. Its tail was said to be
nearly a hundred million miles long, and fifteen million miles broad.
Encke’s Comet (1819). This comet is of extreme interest because of
its change of volume. Moulton says: “On October 28, 1828, it was
135,000,000 miles from the sun, and had a diameter of 312,000 miles.
On December 24, its distance was 50,000,000 miles and its diameter was
14,000 miles; while at its perihelion passage of December 17, 1838, at
a distance of 32,000,000 miles, its diameter was only 3,000 miles.”
Beila’s Comet (1826). This comet has a most interesting history. In
1846 it was again seen; and a month later it had divided into two
parts. They traveled along parallel orbits, some 160,000 miles apart.
In 1852, they were seen to be 1,500,000 miles apart. Since then they
have never been seen. They have, apparently, vanished from the face of
creation!
Donati’s Comet (1858). This comet was visible for more than nine
months. Its tail was estimated as 54,000,000 miles long. Its period of
revolution was more than 2,000 years.
The Great Comets of 1880 and 1882. The latter of these passed through
some hundreds of thousands of miles of the sun’s corona. Its orbit was
not appreciably changed, but, after emerging, it was seen to possess at
least five nuclei--showing the effect upon the comet of the disruptive
forces through which it had passed.
NEBULAE
These are of especial interest, for the reason that they have played
so large a part in forming cosmic theories--the Laplacian, the
Planetestimal, etc. Nebulæ are of various kinds--“Annular Nebulæ,”
resembling a flat, oval, solid ring, having a dark hole in the center.
Then there are “Elliptic Nebulæ,” of varying degrees of eccentricity;
the Great Nebula in Andromeda being a good example. (Numbers of
isolated stars may be found within its limits.) “Spiral Nebulæ” are,
perhaps, the best known of all, and their name accurately describes
their appearance. There are also the so-called “Planetary Nebulæ,” as
well as Nebulous Stars, Irregular Nebulæ, etc. Of late years, much
interest has been centered upon the so-called “Dark Nebulæ.” Herschel
had long before described various “holes in the heavens,” wherein no
stars could be discerned. It is now believed that such spots do not
represent “holes,” as much as dark masses of matter, which seem to
blot out the bright stars behind them. The interested reader may refer
to Hale’s “The Depths of the Universe” for additional information
upon this topic, which is relatively new to astronomy. It is also
interesting to note that the spectra of Nebulæ contain the bright
lines in the green of a substance called “nebulium,” because it is not
found except in nebulæ.
THE MILKY WAY
This is, in a sense, one vast nebula running right round the heavens
in the form of a belt, or ring; its familiar resemblance to spilt milk
being the origin of its popular name. To the naked eye, it appears
merely a hazy band of light, but the telescope shows that it is made
up of an enormous number of stars, millions of miles apart, but which
can only be distinguished from one another by telescopic aid. It
constitutes the so-called “Galaxy.” It seems to be spread out in the
form of a vast disk, whose diameter is many times its thickness. Our
solar system appears to be near the center of this vast system, and, as
we penetrate further and further into space, it becomes apparent that
fewer and fewer stars, and fewer and fewer nebulæ, seem to exist. Hence
the limitation of the material Universe. The Milky Way is made up of
thousands of millions of suns; yet their enormous distances make them
appear to constitute one vast, luminous belt encircling our globe!
THE NUMBER OF STARS
When the heavens are viewed with the naked eye, a few hundred stars may
perhaps be seen--some bright, some faint. Viewed through opera glasses,
many more stars may been seen; while their number is again greatly
increased by the use of a telescope. The larger and more powerful the
telescope employed, the greater the number of stars thus discovered in
the depths of space. The interesting question thus arises: What is the
total number of stars in the entire firmament? Can they be estimated?
And if so, what would their approximate number be?
What we call “stars” are, of course, in practically all cases
_suns_--often vastly larger and hotter than our own. These stars
differ from one another in order of brilliance; some are brighter than
others. They are accordingly classified according to their order of
brilliance, and known as stars of the “First Magnitude,” of the “Second
Magnitude,” etc., up to about the Seventeenth Magnitude. Any star of a
given magnitude is, roughly, about two-and-a-half times as brilliant as
one of the next lower order, and this variation holds throughout--each
magnitude being that much greater in brilliance.
The “magnitude” of the stars varies according to their light-giving
power, and also their distance from us. One of the methods adapted to
measure the magnitude is to compare its brightness with an artificial
star, gradually cutting-off its light by means of neutral, tinted glass
until the two are equal. The color of the star must be taken into
account, in such measurements, the eye being more sensitive to some
colors than to others.
Now, it is an interesting and significant fact that the number of the
stars decreases as their magnitude decreases; that is to say, the
greatest number of stars are found of the first magnitude; a lesser
number of the second; still less of the third, and so on (broadly
speaking). After reaching the ninth magnitude, the number very rapidly
diminishes. It has been calculated that there are about 120,000,000
stars in the first 16 or 17 magnitudes. If the proportion were
maintained throughout, however, there would be more than ten times that
number. Some authorities have asserted that there are, roughly, half a
billion stars of varying magnitudes in the heavens.
THE POSITION OF OUR SOLAR SYSTEM
It has been maintained that our solar system is at, or very near,
the center of the whole Universe. Certain it is that the further we
proceed into space, the less the number of stars encountered, which has
given rise to the suspicion that their number is actually _limited_,
and that the whole Universe consists of a sort of sphere, in which is
enclosed all the stars that exist, and that, beyond this sphere, no
stars whatever remain. No matter exists beyond this point! Such a view
fits in rather well with Einstein’s conception of “curved space,” and a
finite universe of infinite proportions! Of course, it is conceivable
that, outside this vast system, another similar system may exist, and
another and still another; but of such systems we know nothing, and it
seems improbable that proof of their existence could ever be obtained
by man. So far as we can tell, the universe is _One_, and the matter
and energy of that one are limited.
THE MOVEMENT OF OUR SOLAR SYSTEM
It has been shown that our whole solar system is sweeping through space
at the speed of about ten miles a second towards the stars in the
constellation Hercules, and particularly towards Vega, one of its suns.
However, Vega is likewise moving through space, so that by the time our
sun reaches the spot now occupied by Vega (half a million years or so)
Vega will no longer occupy that position, and no “collision” will take
place in consequence! We shall not, in fact, pass very near that star.
DISTANCES OF THE STARS
Astronomical distances are so vast that they can only be measured in
the mind relatively. The distances between the planets in our own
solar system seem big enough; yet they shrink into insignificance when
compared to the distances which separate our whole solar system from
even the nearest of the stars. _Alpha Centauri_ is the nearest star,
and it is separated from us by a distance 276,000 times as great as
that which separates us from our sun. It is approximately 25 billion
miles away. Traveling with the speed of an express train flung into
space, at 40 miles an hour, towards the nearest star, without any
stoppage or any slowing down, we should not arrive at our destination
until after an interrupted flight of 75 million years. Yet this is
our nearest neighbour! Only a _very few_ of the stars are within
400,000,000,000,000 miles of the sun. The great majority of them are
many times this distance from us.
So vast are these distances that some simple means of expressing them
on paper was sought. A “light Year” was finally decided upon as the
_unit_ of measurement--that is, the distance which light would travel
in one year, speeding at the rate of 186,000 miles a second. It has
been estimated that many stars are one, two, three and perhaps five
hundred thousand light-years distant from us in space. The interested
reader may figure-out the number of miles this represents for himself!
TEMPERATURE OF THE STARS
Measurements which have been undertaken prove that the surface
temperature of our Sun is between 5,000°C. and 7,000°C. It is
thought that many stars are considerably hotter than this. We can
form no adequate conception of such intense heat; all matter would
be vaporized; yet, under the enormous pressures which must prevail,
these vapors would in turn be converted into thick, semi-fluid
substances--especially in the interior.
FIXED STARS