OUR NEIGHBORS’ MOVEMENTS.
How high! how distant! how mighty! How little we know about them, yet
how overwhelming the little we know, and how wonderful that we do know
it!
We have now to consider the movements of these distant
neighbors--first, their seeming movements; secondly, their real
movements.
I have already spoken about the seeming motions of the stars as a
whole, once believed to be real, and now known to be only caused by the
motions of our earth. For just as the turning of the earth upon her
axis makes the sun seem to rise every morning in the east, and to set
every evening in the west, so that same continued turning makes the
stars seem to rise every evening in the east and to set every morning
in the west.
When we speak of the stars as rising in the east, we do not mean that
they all rise at one point in the east, but that all rise, more or
less, in an easterly direction--northeast, east, and southeast. So also
with respect to the west. It is to the east and west of the earth as a
whole that they rise and set--not merely to the east and west of that
particular spot on earth where one man may be standing. All night long
fresh stars are rising, and others are setting, and if it were not for
the veil of light made by the sunshine in our atmosphere, we should see
the same going on all day long as well.
There are some constellations, or groups of stars, always visible at
night in our northern hemisphere; and there are some constellations
never visible to us, but only seen by people living in the southern
hemisphere--in Australia, for instance. There are other constellations
which appear in summer and disappear in winter, or which appear in
winter and disappear in summer. This change is caused by our earth’s
journey round the sun. It is not that the constellations have altered
their place in the heavens with respect to the other constellations,
it is merely that the earth has so altered its position in the heavens
that the groups of stars which a short time ago were above the horizon
with the sun by day are now above the horizon without him by night.
Mention has been a good many times made of the axis of the earth ending
in the North and South Poles. If this axis were carried straight onward
through space, a long, slender pole passing upwards into the sky
without any bend, from the North Pole in one direction and from the
South Pole in the other,--this would be the pole of the heavens. The
places of the stars in the sky are counted as “so many degrees” from
the North and South Celestial Poles, just as the places of towns on
earth are counted as “so many degrees” from the North and South Poles
of earth. There are atlases of the sky made as well as atlases of the
earth.
The constellation of the Great Bear is known to all who have ever used
their eyes at all to watch the heavens. Almost equally well known
are the two bright stars in this constellation named the Pointers,
because, taken together, they point in nearly a straight line to a
certain important star in the end of the Little Bear’s tail, not very
distant.
This star, important less from its brightness than from its position,
lies close to that very spot in the heavens where the celestial North
Pole passes. It is called the Pole-star. Night after night, through
the year, it there remains, all but motionless, never going below
the horizon for us in the northern hemisphere, or northern half of
the earth; never rising above the horizon for those in the southern
hemisphere. It shines ever softly and steadily in its fixed position.
If you travel further south, the Pole-star sinks downward towards the
horizon. If you travel further north, the Pole-star rises higher above
the horizon. If you were at the North Pole, you would see the Pole-star
exactly overhead.
[Illustration: CONSTELLATION OF THE GREAT BEAR.]
Very near the Pole-star is the constellation of the Great Bear,
with Cassiopeia nearly opposite on the other side of the Little
Bear, and other groups between the two, completing the circle. These
constellations do not, to us who live in the northern hemisphere,
rise or set; for they simply move in a circle round and round the
Pole-star, never going below the horizon. All day and all night long
this circling movement continues, though only visible at night. It is
caused entirely by the earth’s own motion on her axis.
[Illustration: THE GREAT BEAR 50,000 YEARS AGO.]
[Illustration: THE GREAT BEAR 50,000 YEARS HENCE.]
Lower down, or rather further off from the Pole-star, comes another
ring of constellations. These in just the same manner appear to
travel round and round the Pole-star. But being further away, each
dips in turn below the horizon--or, as we call it, each sets and
rises again. And by the time we come to yet another circle of leading
constellations, we reach those which are so far affected by the
earth’s yearly journey as to be only visible through certain months,
and to be hidden during other months.
[Illustration: CONSTELLATION OF ORION, AS IT APPEARS NOW.]
If we could stand exactly at the North Pole, during part of its six
months’ night, we should see the Pole-star just overhead, and all the
constellations circling round it once in every twenty-four hours. Those
nearest would move slowly, in a small ring. Those furthest, and lowest
down, would in the same length of time sweep round the whole horizon.
But the stars would not there seem to rise or set. If we were standing
at the South Pole, we should see exactly the same kind of seeming
movement, only with altogether a different set of stars. If we were
standing on the Equator at night, we should see the rising and setting
very plainly. The whole mass of stars would appear to rise regularly
and evenly in an easterly direction, to pass steadily across the sky,
each taking its own straightforward path, and to set in a westerly
direction.
We who are placed midway between the Pole and the Equator, see a
mixture of these two motions. Some stars seem to circle round and
round, as all would do if we stood at the North Pole. Some stars seem
to rise and set, as all would do if we stood at the Equator. So much
for the seeming movements of the stars.
But now, about their real movements. Are the stars fixed, or are they
not? These seeming daily and yearly motions do not affect the question,
being merely caused by our own motions. Trees and hedges may appear to
move as we rush past them in a train, yet they are really fixed.
[Illustration: CONSTELLATION OF ORION 50,000 YEARS FROM NOW.]
During a long while, after it was found out that the quick, daily
movements of all the stars in company were merely apparent, men
believed that they really had no “proper motions”--that is, no
movements of their own. For century after century the constellations
remain the same. Hundreds of years ago the seven chief stars of the
Great Bear shone in company as they shine now. Who could suppose that
each one of those seven stars is hurrying on its path through space
with a speed exceeding far that of the swiftest express-train? Yet so
it is. Hundreds of years ago the grand group of Orion, with belt and
sword, gleamed brilliantly night by night as it gleams in these days;
and Cassiopeia had her W form, and Hercules and Draco and Andromeda
were shaped as they are shaped still. Who would imagine that through
those hundreds of years each star of these different constellations was
hastening with more or less of speed along its heavenly road? Yet so it
is.
Cases have been decisively ascertained of stars changing their places
among the other stars by a slow and gradual motion. Three of the most
conspicuous of them--Sirius, Arcturus, and Aldebaran--have been proved,
by the comparison of modern with some ancient observations, to have
experienced a change of place to the southward, to the extent of more
than the breadth of the moon in all the three. And during the period of
accurate modern measurement, other instances have been ascertained of
steady change of place by the effect of proper motion.
But if the stars are thus rapidly moving in all directions, how is it
that we do not _see_ them move? How is it that, night after night, year
after year, century after century, even thousand years after thousand
years, the shapes of the constellations remain unaltered?
Suppose you and I were standing on the seashore together, watching
the movements of scores of sea-craft, little boats and large boats,
steamers, yachts, and ships. Suppose we stood through a full quarter
of an hour looking on. Some might move, it is true, very slowly; yet
their movements in every case would plainly be seen. There could be no
possibility of mistaking the fact, or of supposing them to be “fixed.”
Just so we see the nearer planets move. Little danger of our supposing
them to be “fixed stars.”
In the matter of the stars themselves, we must carry our illustration
further. Come with me up to the top of that lofty hill on the border
of the sea, and let us look from the cliff. We see still the movements
among boats and smacks, yachts and steamers, only the increased
distance makes the movements seem slower. But our view is widened. Look
on the far horizon and see three distant dots, which we know to be
ships--one and two close together, and a third a little way off, making
a small constellation of vessels. Watch them steadily for a quarter of
an hour. You will detect no movement, no increased distance or nearness
between any two of the three. The group remains unchanged.
Are they really moving? Of course they are, more or less rapidly,
probably with differing speed and in different directions. But at
so great a distance, one quarter of an hour is not long enough for
their motions to become visible to the naked eye. If we could watch
longer--say, for two or three hours--ah, that would make all the
difference! If only we could watch longer! But the hundreds, and even
thousands of years during which men have watched the stars, sink, at
our vast distance, into no more than one quarter of an hour spent in
watching the far-off ships from the high hilltop. The motions can not
be detected. In ten thousand years you might see something. In fifty
thousand years you might see much. But four or five thousand years are
not sufficient.
One other mode there is, by means of which the movements of the ships
on the horizon might be made plain. Suppose you had no more than the
quarter of an hour to spare, but suppose you had at your command a
powerful telescope. Then you may practically bring the ships nearer,
and by magnifying the small, slow, distant motions, you may make them,
as it were, larger, quicker, more easy to see.
Telescopes will do this for us, likewise, in the matter of the stars.
By means of telescopes, with the assistance of careful watching and of
close calculation it has been found that the stars are really moving
quickly, each one in his own pathway. The very speed of some of them
has been measured.
Arcturus is one of those stars, the motions of which are most plainly
to be seen. In the course of about one thousand years he changes
visibly his place in the sky by a space equal to the apparent diameter
of the moon. The seeming movement of Arcturus in one thousand years is
the same as the seeming width of the round moon that we see.
But the actual speed with which Arcturus rushes through space is said
to be no less than fifty-four miles each second, or not far from two
hundred thousand miles an hour. That is nearly three times as fast as
our own earth’s motion round the sun. How enormous the distance must be
which can shrink such speed to such seeming slowness!
Another beautiful star, Capella, is believed to travel at the rate of
thirty miles each second. The speed of Sirius is slower, being only
fourteen miles a second. The Pole-star creeps along at the rate of only
one mile and a half each second.
So also with the rest of the stars. There seems good reason to believe
that every star we see shining in the heavens, every star visible in
powerful telescopes, is perpetually hastening onward. But hastening
whither? God knows! We do not.
In all probability not one of the tens of millions of stars which
may be seen through telescopes is in repose. This is a matter of
conjecture, of reasoning from analogy, and of reasoning also from
the working of known laws. We _know_, as a consequence of direct
observation, apart from the new spectroscopic method, that at least
hundreds are upon the wing. We _assume_, as a matter of the greatest
possible likelihood, that all the millions besides, which can not be
actually seen to stir, are equally on the move. Knowing what we do know
of the laws by which the universe of stars is governed, it seems to us
an absolute impossibility that any single star, amid the whole vast
host, can be or could be permanently at rest.
If by any means a star were brought to repose--what then would happen?
It would inevitably start off again, drawn by the attraction of other
stars. From whatever direction the strongest pull came, the impulse
would be given. Lengthened repose would be out of the question. And
this, it seems to us, must be true, not of one star only, here or
there, but of every star in the enormous host of radiant suns which
make up the mighty Stellar System.
Our forefathers, one thousand years ago, could not measure the precise
positions of individual stars, as astronomers now are able to do.
They had no modern observatories, no telescopes, no spectroscopes, no
photographic appliances. These methods of observation we shall explain
in another chapter. Their measurements at best were rough, their
scientific knowledge was crude. Had we any such accurate observations
handed down from one thousand years ago as are made in these days, we
should no doubt see clearly many slight differences in the positions
of many stars which are not now apparent. But even then we should see
no changes sufficient in amount to affect the general outlines of the
leading constellations.
A star, which in the course of a century makes visible advance over a
space in the sky equal to only a small portion of the breadth of the
full moon, is looked upon as a fast voyager. One hundred times this
degree of movement, if it took place in a considerable number of stars
in our sky, would not in centuries very materially change the face of
our midnight heavens.
And all motions which would in the remotest degree affect the shapes of
constellations, must be sideway motions. Those line-of-sight motions,
of which the spectroscope alone tells us, could never have been
discovered by simple observation of the sky. Until the new method came
to light we had no means whatever of perceiving such movements among
the stars.
Suppose you are looking at two men in the distance, upon a wide, flat
plain. One of the two is walking very slowly _across_ your line of
vision. The second man is moving very slowly straight _towards_ you.
If you watch with care you may find out both the movements. The sideway
walking will be apparent first and most easily, because, as the man
moves, he has constantly a fresh part of the horizon behind him. But
in time the advance of the second man towards you will also become
apparent; for although he is seen still against precisely the same spot
on the horizon, he slowly occupies a larger spot on the retina of your
eye,--in other words, he seems to grow bigger. And that, as you know
from long experience, can only mean increasing nearness.
If a star seemed to grow larger as it drew nearer, we should then be
able to perceive that movement also. But no star in the sky ever does
seem to grow any larger. Every star is to us but one point of light.
It may be rushing towards us at an enormous rate of speed, yet still
as a single point it remains, always at the same point in our sky.
Therefore we have no chance of perceiving its movement; or rather, we
_had_ no chance until the discovery of this new method. In fact, the
very nearest known star is at so enormous a distance that, supposing it
to be coming towards us at the rate of one hundred miles each second,
it would still gain, in the course of a century, only one-fortieth part
more of brightness than it has now. It would not increase at all in
apparent size.
When we leave behind us the thought of starry motions, as we faintly
detect them at this great distance, and picture to ourselves the actual
far-off whirl of all those glorious suns, the effect upon the mind is
overwhelming. Stars are found to be rushing hither and thither, at
every degree of speed, in every imaginable direction: stars to right,
and stars to left; stars towards us, and stars away from us; stars
alone, and stars in company,--all this, and more, deciphered out of
the tiny gleam of quivering light, which streams through the vast
abyss of space from each distant orb to earth. So real star-motions
were known--first, through telescopic observation; secondly, through
spectroscopic observation; and now, lastly, photography has stepped in,
bringing with it much increase of exactitude.
But if all the stars are moving, what of our sun? Our sun is a star.
And our sun also is moving. He is pressing onward, in a wide sweep
through space, bearing along with him his whole vast family--planets,
satellites, comets, meteorites--round or towards some far distant
center. For aught we know, every star in the heavens may have a like
family traveling with him.
In infinite space the stars are strewn in immense clusters, like
archipelagoes of islands in the ocean of the heavens. To go from one
star to another in the same archipelago light takes years; to pass
from one archipelago to another it takes thousands of years. Each of
these stars is a sun similar to ours, surrounded, doubtless, at least
for the most part, by worlds gravitating in its light; each of these
planets possesses, sooner or later, a natural history adapted to its
constitution, and serves for many ages as the abode of a multitude of
living beings of different species. Attempt to count the number of
stars which people the universe, the number of living beings who are
born and die in all these worlds, the pleasures and pains, the smiles
and tears, the virtues and vices! Imagination, stop thy flight!
The sun is not one of the most quickly-moving stars. His rate of speed
has not been found out with any certainty, but it is believed to be
about four or five miles a second.
And where are we going? This has been in part discovered. If you and
I were driving through a forest of trees, we should see the trees on
each side of us seeming to move backward, while behind they would close
together, and in front they would open out.
Astronomers--and first among them, William Herschel--reasoned that
if our Solar System were really in motion, we ought to be able to
see these changes among the stars. And some such changes have become
visible through careful watching--not so much those ahead and behind as
those at the sides.
It is not actually so simple a matter as looking at the trees in a
forest, because the trees would be at rest, whereas each star has his
own particular real motion, as well as his seeming change of place
caused by our sun’s motion. It is more like moving in a small steamer
at sea, among hundreds of other craft, each of which is going on its
own way, at the same time that all on either side seem to move backward
because we are moving forward.
So each movement had to be noted, and the real motions had to be
separated from the seeming backward drift of stars to the right and
left of the sun’s pathway. The result of all this is that the sun,
with his planets, is found to be hastening towards a certain far-off
constellation named Hercules.
It is a strange and unexpected fact, but absolutely true, that each sun
of space is carried along with a velocity so rapid that a cannon-ball
represents rest in comparison; it is at neither a hundred, nor three
hundred, nor five hundred yards per second that the earth, the sun,
Sirius, Vega, Arcturus, and all the systems of infinitude travel: it
is at ten, twenty, thirty, a hundred thousand yards a second; all run,
fly, fall, roll, rush through the void--and still, seen as a whole, all
seems in repose.
The immense distance which isolates us from all the stars reduces
them to the state of motionless lights apparently fixed on the vault
of the firmament. All human eyes, since humanity freed its wings
from the animal chrysalis, all minds since minds have been, have
contemplated these distant stars lost in the ethereal depths; our
ancestors of Central Asia, the Chaldeans of Babylon, the Egyptians of
the Pyramids, the Argonauts of the Golden Fleece, the Hebrews sung by
Job, the Greeks sung by Homer, the Romans sung by Virgil,--all these
earthly eyes, for so long dull and closed, have been fixed, from age
to age, on these eyes of the sky, always open, animated, and living.
Terrestrial generations, nations and their glories, thrones and altars
have vanished: the sky of Homer is always there. Is it astonishing
that the heavens were contemplated, loved, venerated, questioned, and
admired, even before anything was known of their true beauties and
their unfathomable grandeur?
Better than the spectacle of the sea, calm or agitated, grander than
the spectacle of mountains adorned with forests or crowned with
perpetual snow, the spectacle of the sky attracts us, envelops us,
speaks to us of the Infinite. “I have ascended into the heavens, which
receive most of His light, and I have seen things which he who descends
from on high knows not, neither can repeat,” wrote Dante in the first
canto of his poem on “Paradise.” Let us, like him, rise towards the
celestial heights, no longer on the trembling wings of faith, but
on the stronger wings of science. What the stars would teach us is
incomparably more beautiful, more marvelous, and more splendid than
anything we can dream of.
How do such contemplations enlarge and transfigure the vulgar idea
which is generally entertained of the world! Should not the knowledge
of these truths form the first basis of all instruction which aims
at being serious? Is it not strange to see the immense majority of
human beings living and dying without suspecting these grandeurs,
without thinking of learning something of the magnificent reality which
surrounds them?
Where the sun and his planets will journey in future ages no living man
can say. Indeed, though it is a question which does not lack interest
to a thoughtful mind, yet there are numberless other questions about
centuries near at hand which concern man far more nearly. The history
of the Universe, and the history of this Earth of ours, must have
advanced many broad stages before our sun and his attendant planets can
have traveled so far that any change will be apparent in the shape of
the star-constellations which spangle our sky.