their positions in the heavens for long periods of time together. There
are, of course, no “fixed” stars at all since every celestial body is
moving with greater or lesser rapidity through space; but these stars
are so far distant from us that such movements are inappreciable,
even after long periods of time, and in spite of the most careful
observations. In comparison with the more rapidly moving heavenly
bodies, they do not appear to “move,” and have been denominated “fixed
stars” in consequence.
DOUBLE STARS
A large number of stars appear single, when viewed by the naked
eye, but when seen through a powerful telescope, are seen to be, in
reality, two stars which revolve round one another. Many thousands of
such double stars are now known to exist; indeed, apparently single
stars have been found, upon closer examination, to be composed of
a group of four or five or more stars--so that the name “multiple
stars” has been given to such groups. They are near one another in the
astronomical use of that word--though they may actually be hundreds
of thousands, or millions of miles apart. Many of these double stars
seem to be quite separate from one another. Others appear to have some
physical connection. Those which are known to form systems are known as
_binaries_.
COLORED STARS
Many of the double stars exhibit curious and beautiful phenomena
of complementary colors. In such cases, the larger star is usually
more or less reddish or orange, and the smaller one bluish-green or
greenish-blue. Many of the double stars, on the contrary, are of the
same color. There are white, red, blue, orange, green and yellow
stars. The planets also vary greatly in color--Venus, e.g., being
white, Mars reddish, etc. Inasmuch as the planets only reflect light,
however, this is due to quite different causes; the other colored stars
are self-luminous suns which emit light of their own.
VARIABLE STARS
In addition to variations in the color of stars, they also vary greatly
in brilliance, and certain stars are much brighter at times than at
others. In some cases these changes in brilliance are regular; in
others, irregular. “Omicron,” for example, which, Bayer recorded in
his Atlas in 1603, is a regular variable; its period of change is 331
days, 8 hours; in other words, it reaches its greatest brightness about
12 times in 11 years, when it sometimes attains the brilliancy of a
star of the 2nd magnitude, at which brilliancy it remains stationary
for about a fortnight. It then diminishes during about three months,
until it sinks down to a star of magnitude 9½, or even becomes totally
invisible. It remains in this condition for about 5 months, and then
gradually recovers--during the next following 3 months--its maximum
brilliancy. In other words, its brilliancy is absolutely periodic.
Other variables are by no means regular, however, but “come and go” at
different intervals.
Various theories have been advanced by way of explanation--one of
the simplest being that such stars are in reality double, one being
luminous and the other not; and that, during their revolutions, the
non-luminous star partially or totally eclipses the bright one, at
stated intervals. The whole subject, however, is difficult, and much
yet remains to be learned concerning these variable stars.
TEMPORARY STARS
From time to time, stars have suddenly appeared in the heavens, where
no star existed before! Such stars have usually become increasingly
brilliant for a short period of time, and then as suddenly died
away again, leaving no trace of their existence behind them. These
“new stars” for long puzzled astronomers. The theory often advanced
to explain them is that some distant star has “exploded,” and the
increasing brilliance which we see is the result. If such were the
case, its sudden dimming-down and disappearance would be quite
intelligible--as would be its sudden appearance. A large number of
such stars have now been recorded, and their existence is no longer in
doubt. In some cases, they have remained visible for weeks or months
before their final disappearance.
STAR GROUPS--CLUSTERS
Here and there throughout the sky are places where the brighter stars
seem to be clustered. These families of stars are of such magnificent
proportions as to stagger the imagination. Among the best known are the
Pleiades, the Hyades, Coma Berenices and Orion. Although they appear to
us very close together, they are not really so, being usually several
hundreds of thousands of miles apart. Many of these star-groups
are irregular; but numbers of them constitute clusters, which are
of various sizes and shapes. Perhaps the most interesting are the
so-called “globular clusters,” because they present the appearance of
stars having been massed together as globes. Some of them contain five
or six thousand stars. Although they appear to us so close together,
it has been calculated that, in a cluster containing 5,000 stars the
average distance of the stars from one another would be 30,000 times
the distance of the sun from the earth! The vast distances of space
considered in astronomy may perhaps be realized by this fact--when
it is considered that such a cluster appears to us as a single star,
only capable of being separated into its component parts by means of
high-powered telescopes!
ECLIPSES
The total eclipse of the Sun, January 24, 1925, brought the subject of
eclipses to the public attention as never before, and many thousands
of persons watched that beautiful and impressive sight through smoked
glasses or strips of film.
When we speak of eclipses, we usually mean an eclipse of either the Sun
or the Moon. How are such eclipses caused?
A total or partial eclipse of the sun is caused by the moon passing
between the earth and the sun, the three celestial bodies forming, as
it were, a straight line. The sun is then shut-off from the vision
of the inhabitants of our globe over a certain, limited area of its
surface. The shadow cast by the moon falls across the earth.
But how is the moon eclipsed? Certainly the sun does not pass between
the moon and the earth, on such occasions! What causes the moon to be
eclipsed?
The answer is as follows: Inasmuch as both the earth and the moon are
illuminated by the sun, they both cast long shadows into space, as any
solid body does, when held in front of a strong light. The earth’s
shadow trails away for thousands of miles into space. Into this shadow
the moon enters, and when it does so, it becomes eclipsed--totally or
partially, as the case may be. Total eclipses are instances when the
whole surface of the celestial body is apparently covered; partial
eclipses are those in which only a portion of the body is dark--the
remainder being still visible.
In addition to eclipses, two other astronomical phenomena of interest
should here be mentioned: _Transits_, and _Occultations_. By “transit”
is meant the passage of some other heavenly body between ourselves and
the sun. Thus, Mercury and Venus, both lying nearer the sun than the
earth, occasionally pass in front of it. We then have a transit of
Venus, or a transit of Mercury, as the case may be.
By “Occultation” is meant the hiding of one heavenly body by
another--as when the moon hides some other planet or star, or one
planet hides another planet or star. The three bodies are then “in
line” as before. Of course, all eclipses represent instances of
Occultation.
TELESCOPES
Telescopes are of relatively recent origin; the ancients were forced
to make their observations without them, which makes some of their
conclusions all the more remarkable. There is considerable evidence
that the builders of the Great Pyramid employed the “Grand Gallery” for
astronomical observations (see “The Great Pyramid of Egypt,” in the
present series), and other devices were employed. But no telescopes of
any great power of magnification existed before the last century, while
our present marvelous instruments of precision are the evolution of the
present century.
Telescopes are of two kinds: refracting and reflecting. Any small
telescope exemplifies the former; the incoming light-rays are focussed
by a series of lenses, and directly observed by the eye. In the
employment of reflecting telescopes, however, another principle is
employed: the incoming light-rays are caught and reflected by means
of a curved mirror, and focussed on a lens, which in turn is inserted
in an elaborate eye-piece, in which the light-rays are magnified and
measured. Some of the modern instruments have a forty or more inch
aperture, and are capable of enormous powers of magnification.
THE SPECTROSCOPE: SPECTRUM ANALYSIS
For more than two thousand years, astronomy remained a purely
mechanical and mathematical science, being limited to observations and
deductions therefrom; but in 1860 the method of spectrum-analysis was
discovered. This was a most revolutionary discovery, inaugurating, as
it did, the whole science of astro-physics; and enabling us to know as
much of the physics and chemistry of distant stars and nebulæ--their
nature, constitution, and temperature--as we know of the planets of our
own system! Even the existence of otherwise invisible stars has been
demonstrated in this manner--their orbits, rate of motion, and mass.
The science of astro-physics is now one of the most exact in the whole
realm of science; and has only been rendered possible by the invention
of the spectroscope. As this instrument plays such an important part
in all astronomical research, a brief explanation of the instrument
becomes necessary.
If a ray of sunlight be passed through a glass prism, the ray is split
up into its primary colors; so that, instead of a single spot of white
light being visible a narrow band of brilliant colors is seen--ranging
from red to violet. But this is not the most important part of the
discovery. When this spectrum was closely examined, it was found to
be crossed by numerous black bands of various thicknesses. Sometimes
these occurred in groups, sometimes singly. By enlarging the spectrum
by passing it through several prisms, as many as 3,000 of these bands
could be counted. The nature and explanation of these strange bands
of blackness remained long uninterpreted, however. It remained for
Kirchoff, in 1860, to discover their uses and significance.
Briefly, it is this. The chemical elements, when heated to a state
of incandescence, present each one its own characteristic spectrum;
each one has its own peculiar markings, or band of lines. No two
elements are exactly like in their bands, as shown in the spectrum.
Hence, whenever that particular marking is observed, it becomes certain
that that element, and none other, is present. These spectra are very
varied; iron, for example, has more than 2,000 such bands, while lead
and potassium have but one each.
In this way--all the chemical elements having been studied, and their
characteristic bands known--it became possible to explore the stars,
planets and suns, and discover their chemical composition. For, no
matter where an element was discovered--on this earth or on the
remotest star--it would always cast its particular spectrum, when thus
examined. The effect of all this upon astronomy can be perceived at
once. Not only the heavenly bodies known to us, but those which have
never been seen by human eye--even when aided by the most powerful
telescopes--can be studied and their chemical composition and structure
accurately determined. Here is progress indeed!
All this becomes the more remarkable when we stop to consider the
immense distances of space, and how widely separated the heavenly
bodies are from one another. This may, perhaps, be shown by one or two
illustrations. We are, roughly, about 93,000,000 miles from our own
sun. Now, the majority of the stars we see are suns, like ours. The sun
next removed from us in space is about 275,000 times as far from us as
we are from our sun. The orbit of Halley’s comet, of which so much has
been written lately, is some 3,280,000,000 miles in length; and this
sporadic body, coursing through space at a speed 50 times greater than
a rifle bullet, takes 75 years to complete its circuit. The nearest
star has been calculated to be nearly 25 trillion miles away; while
some of the stars are 40 times as far from us as that!
PHOTOGRAPHY
The second great engine of astronomical research, that has been added
during the past century, is _photography_. By this means exact maps
may be taken of the heavens at any hour of the night, and the precise
position of thousands of stars determined with the utmost exactitude.
A chart of the heavens, made in this manner, is not only more complete
but more accurate than the combined observations of any number of men
could possibly be. Moreover, the photographic plate will record the
existence of stars which cannot be seen even with the aid of the most
powerful telescopes. This is due to the fact that the plate gradually
collects light, and its _cumulative_ effect is noticeable, when its
_immediate_ effect cannot be perceived. This power of photographic
plates is most valuable, and cannot be duplicated in any other manner.
We are assured on good authority that “an ordinary good portrait camera
with a lens three or four inches in diameter, if properly mounted so
that an exposure of several hours can be made, will show stars so
minute that they are invisible even in the great Lick telescope.” An
international photographic chart of the heavens is now under way,
which, when finished, will represent an accurate catalog of every
visible sun, star, and planet, in the sky. After this, any unusual body
should be quickly discovered.
But photography is employed not only for mapping out the heavens, but
for reaching the farthest stars. The moon and the sun have both been
photographed repeatedly, and with most instructive results. The first
good pictures of the moon were made by Dr. John W. Draper of New York
City, in March, 1840. His son, Dr. Henry Draper, succeeded him in this
work, and his photographs were considered the best until Rutherfurd
began his remarkable work in 1865. After this, much important work
was done in the Lick observatory, and elsewhere. The first picture of
the sun was taken in 1845, by Fizeau and Foucault, on a daguerreotype
plate. Sun spots, total eclipses, etc., are now studied in great detail
by this means.
THE TIDES
Every particle of matter attracts every other particle of matter
throughout the entire Universe. The Sun and the Moon both exert a
definite pull upon the earth; the moon particularly, being the earth’s
satellite, is (so to say) held in place by the earth. The moon,
exerting this definite pull, naturally influences the water of the
earth most of all, because water is a fluid, mobile body. A heaping-up
of the water then occurs--“high tide.” But the moon also attracts the
earth to some extent; and the consequence of this is that the water
on the opposite side of the globe is, as it were, left behind, which
causes a heaping-up of the water there also. Hence, there are two high
tides daily, with an interval of 12 hours between them, on opposite
sides of the globe.
When the sun and moon pull together, we have the highest tides--“spring
tides.” When they do not pull together (being in different parts of the
heavens) we have only the surplus pull of the moon over the sun, and
the tides are consequently not so high. These are the “neap tides.” All
tides act as a sort of check or brake upon the rotation of the earth on
its axis--tending to slow down its speed to some extent. “Tidal waves”
are due to a combination of special causes.
GRAVITATION
The mysterious influence or “pull” which various celestial bodies
exert upon one another is known as gravity or gravitation. We know
that masses of matter attract one another according to their size;
the larger the body, the greater the force exerted, etc. Further, the
influence decreases according to a definite law--according to the
square of the distance between the two bodies. The innermost nature
of gravitation is still largely a mystery--though various ingenious
theories have been advanced in order to explain it. (See my article
in “The Monist,” for July, 1913, and pp. 44-46 of “New Discoveries
in Science” in the present series.) Gravitation is supposed to act
throughout the whole Universe, so that all celestial bodies mutually
influence one another, to some extent. Its speed, mode or action, etc.,
as well as its essence or true nature are, however, unknown even yet;
they are still unsolved mysteries!
THE ETHER
At all events, gravitation is thought to act through, or by means of,
the Ether--the nature of which is still another mystery! Lodge, in his
“Ether of Space,” has given some interesting figures as to the enormous
strain which the ether must be supposed to transmit or carry. Lack
of space, however, prevents a further discussion of this interesting
question; a brief summary may be found on pp. 53-55 of my book on
“Chemistry for Beginners,” in the series of Blue Books. For our present
purposes, it need only be said that the ether is the only hypothetical
connecting-link between celestial bodies--since there is no air or
atmosphere in interstellar space. And it is across or by means of this
ether that gravitation must be exerted.
ATOMIC ANALOGIES
Recent investigations of the innermost structure of the atom have
shown us that it is probably constituted on very much the same plan
as our solar system--a central “sun” or proton, round which revolve
the negative planets or “electrons.” This question I have treated more
fully in my “Chemistry for Beginners,” pp. 42-44, to which the reader
is referred.
THUNDER AND LIGHTNING
The lightning flash is merely a huge electric spark, such as may
be seen between the terminals of any electric machine. In cases of
flashes, or forked lightning, this “spark” is seen directly. Sheet
lightning is observed when the original flash is hidden behind clouds,
and only its reflection or effects are seen. The rumbling of thunder is
due to the reverberations and echoes of the original “peal.” The peal
is thought to be due to the sudden rushing together of the molecules of
the upper atmosphere, which have been rent asunder by the flash--a sort
of vacuum created. Camille Flammarion has written an interesting book
on “Thunder and Lightning,” which may be consulted for further details.
FIREBALLS
These are virtually the same as “shooting stars” (_q.v._,) and no
essential difference can be pointed to, as to their origin or nature.
They are not mere “blobs” of lightning, but solid bodies which
sometimes burst, with a great noise--though they are usually noiseless.
Many of them appear to be pear-shaped, but they may be seen to change
their size and shape during the period of visibility. Fireballs are
often accompanied by a train of sparks.
ATMOSPHERIC ELECTRICITY
The surface of the earth is constantly charged with negative
electricity of a static character. The upper atmosphere is usually
charged positively, though, this may vary according to circumstances.
The earth and upper air thus resemble two sheets of tin-foil, with
the air an imperfect dialectric between them. This may be broken
down, especially in wet or damp weather. The effects upon the mental
and physical health are often very noticeable (see Dexter: “Weather
Influences,” etc.)
THE EARTH’S MAGNETISM
It has long been known that the magnetic pole does not coincide with
the North Pole (or South Pole). The compass points to the magnetic
north pole, and not to the true north pole. Lines of magnetic force
seem to envelop the earth, terminating at the north and south poles,
respectively. Although this is purely a terrestrial phenomenon, it is
necessary to mention it here, since it has enabled us to explain, very
largely, the remarkable manifestation known as
THE AURORA BOREALIS
This is usually seen in northern climes, and the reason for this is
now clear. We know that the corpuscles discharged from a Crookes tube
are deflected by a magnet. These corpuscles are discharged in immense
numbers by the sun, and rain upon our earth. Now, the earth is a
magnet, and these corpuscles are caught by the lines of force girdling
our earth, and carried towards the poles, where they find themselves
in an atmosphere comparable with high vacua. They then begin to give
out the shifting and darting lights characteristic of the cathode rays,
causing a certain luminosity. These darting and shifting lights would,
on this theory, account for the Aurora Borealis--which is also known to
vary with the number of sun-spots.
TIME: MEASUREMENT OF:
Our divisions of time are purely arbitrary, and are all based upon
the revolution of our earth upon its axis, which thus constitutes
a gigantic clock. All other clocks, watches, etc., are adjusted
accordingly. This is really our only way of measuring time; subjective
feelings are very illusory, and have to be checked-up by other means.
The solar day is the basis of all our calculations--a month, a year,
etc., being only so many days in length. Our earth, therefore, is the
clock by which we measure the time of the Universe!
SPACE: MEASUREMENT OF:
The measurement of space is always a difficult problem, even for
near-by objects (see my “Psychology for Beginners”). When applied to
celestial bodies, it becomes immensely complicated, and the only wonder
is that such apparently accurate measurements have in fact been made!
Such measurements cannot, of course, ever be made _directly_, but must
depend upon trigonometry and abstruse mathematical calculations. Most
of them are based upon the following principles: If we observe a
distant object from two different points-of-view, at a known distance
apart, the angle formed by imaginary lines running from the object to
one position, and to the other, can readily be calculated. Knowing
this angle, much can be ascertained as to the size, distance, etc., of
the distant body. If a distant star be viewed from opposite sides of
the earth, we have here a known base-line of slightly more than 8,000
miles. But this is altogether too small for astronomical distances! A
much longer base-line must be sought. Accordingly, observations are
made of a distant star when the earth is (so to say) “north” of the
sun, and further observations of the same star when the earth is (so
to say) “south” of it--six months later, when the earth has traveled
half-way through its orbit round the sun. The diameter of the earth’s
orbit being known (186,000,000 miles, almost) we have here a base-line
of this size for use in our measurement of the angle and subsequent
calculations. Immense as this base-line is, however, it is too small
for our purposes, for so immense are astronomical distances, that _no
change whatever_ can be observed in the relative positions of certain
fixed stars--even when studied from such different positions in space!
In other words, the star is so far distant that, when viewed from two
positions in space, distant from one another nearly one hundred and
eighty-six million miles, it appears to occupy the same position! But a
mere summary of this question, and its details would involve an entire
volume in itself!
THE INTERNATIONAL DAY LINE
Inasmuch as our earth revolves on its axis, a new day is beginning
at some different moment all round the world. This being the case,
how are we to fix some definite and official “starting point” for our
day--since the day officially begins at midnight, and not at sunrise?
To determine this, an arbitrary International Day Line has been drawn,
on the 180th meridian--just half way round the globe from Greenwich.
Fortunately, this falls in the Pacific Ocean, where there is almost
no land. When the sun crosses this line, a new day begins. I have
explained this more fully in my book “New Discoveries in Science” in
the present series (pp. 40-42).
CALENDARS, ETC.