NEIGHBORING FAMILIES.
We have now to take flight in thought far, far beyond the outskirts of
our little Solar System. Yes, our _great_ Solar System, with its mighty
sun, its planets, its moons, its comets and meteorites, its ceaseless
motions, its vast distances,--even all this sinks to littleness beside
the wider reaches of space which now have to be pictured to our minds.
For our sun, in all his greatness, is only a single star--only one star
among other stars--and not by any means one of the largest of the stars.
How many stars are there in the sky? Look overhead some cloudless
night, and try to count the brilliant points of light. “Millions,” you
would most likely give as your idea of their number. Yet you would be
wrong; for you do not really perceive so many. The stars visible to
man’s naked eye have been mapped and numbered. It is found that from
two to three thousand are, as a rule, the utmost ever seen at once,
even on a favorable night, and with particularly good sight.
But what is actually the full number of the stars? Two or three
thousand overhead. Five or six thousand round the whole world. So
much visible to man’s unaided eyes. Ah, but take a telescope, and see
through it the opening fields of stars beyond stars. Take a stronger
telescope, and note how, as you pierce deeper into space, fresh stars
beyond fresh stars shine faintly in the measureless distance. Take the
most powerful telescope ever made, and again it will be the same story.
There has been a chart or map drawn of known stars in the northern
hemisphere--including those visible in telescopes down to a certain
magnitude--containing over three hundred thousand. But that is only a
part of even what man can see. Sir William Herschel calculated roughly
that the number of stars within reach of his powerful telescope, round
the whole earth, amounted probably to something like twenty millions.
Twenty millions of suns! For that is what it really means. Twenty
millions of radiant, burning, heavenly bodies--some the same size as
our sun; some larger, perhaps very much larger; some smaller, perhaps
very much smaller; but all SUNS. And any number of these suns may have,
just like our own, families of planets traveling round them, enjoying
their light and their heat.
We talk about stars of the first, second, and other magnitudes. Stars
can be seen without a telescope as low down as the sixth magnitude;
after that they become invisible to the naked eye. This word
“magnitude” is rather misleading. “Magnitude” means size, and whatever
the real size of the stars may be, they have to our sight no seeming
size at all. So when we speak of different _magnitudes_, we really mean
different _brightnesses_. The brightest stars are those of the first
magnitude, the next brightest those of the second magnitude, and so on.
No doubt many a star of the third or fourth magnitude is really much
larger than many a star of the first or second magnitude, only being
farther away it shines more dimly, or the higher-magnitude star may in
itself possess greater natural brilliancy.
Of first-magnitude stars there are altogether about twenty; of
second-magnitude stars about sixty-five; of third-magnitude stars about
two hundred; and so the numbers increase till of the sixth-magnitude
stars we find more than three thousand. These are all that can be
commonly seen with the naked eye, amounting to five or six thousand.
With telescopes the numbers rise rapidly to tens of thousands, hundreds
of thousands, and even millions.
For a long while it was found quite impossible to measure the distances
of the stars. To this day the distances of not over two dozen, among
all those tens of thousands, have been discovered. The difficulty of
finding out the distance of the sun was as nothing compared with the
difficulty of finding out the distances of the stars.
No base-line sufficient for the purpose could for years be obtained.
I must explain slightly what is meant by a “base-line.” Suppose you
were on the brink of a wide river, which you had no means of crossing,
though you wished to discover its breadth. Suppose there were on the
opposite brink a small tree, standing alone. As you stood, you would
see the tree seeming to lie against a certain part of the country
beyond. Then, if you moved along your bank some fifty paces, the tree
would seem to lie against quite a different part of the country beyond.
Now if you had a long piece of string to lay down along the fifty paces
you walked, and if two more pieces of string were tied, one from each
_end_ of the fifty paces, both meeting at the tree, then the three
pieces of string would make one large triangle, and the “fifty paces”
would be the “base” of your triangle.
If you could not cross the river, you could not of course tie strings
to the tree. But having found your _base-line_, and measured its exact
length, and having also found the shape of the two angles at its two
ends, by noting the seeming change of the tree’s position, it would
then be quite easy to find out the distance of the tree. The exact
manner in which this calculation is made can hardly be understood
without some slight knowledge of a science called trigonometry. The
tree’s distance being found, the breadth of the river would be known.
This mode of measuring distance was found comparatively easy in the
case of the moon. But in the case of the sun there was more difficulty,
on account of the sun’s greater distance. No base-line of ordinary
length would make the sun seem to change his position in the sky in the
slightest degree. Nor till the very longest base-line on the earth was
tried could the difficulty be overcome. That base-line is no less than
eight thousand miles long. One man standing in England looking at the
sun, and another man standing in Australia looking at the sun, have
such a base-line lying between them, straight through the center of the
earth.
In the case of the stars this plan was found useless. So closely has
the sky been mapped out, and so exactly is the place of each star
known, that the tiniest change would have been at once noticed. Not
a star showed the smallest movement. The eight thousand miles of the
earth’s diameter was a mere point with regard to them.
A bright idea came up. Here was our earth traveling round the sun, in
an orbit so wide that in the middle of summer she is over one hundred
and eighty millions of miles away from where she is in the middle of
winter. Would not that make a magnificent base-line? Why not observe
a star in summer and observe the same star again in winter, and then
calculate its distance.
This, too, was done. For a long while in vain! The stars showed no
signs of change, beyond those due to causes already known. Astronomers
persevered, however, and with close and earnest care and improved
instruments, success at last rewarded their efforts. A few--only a few,
but still a few--of those distant suns have submitted to the little
measuring-line of earth, and their distance has been roughly calculated.
Now, what is their distance? Alpha Centauri, the second star which was
attempted with success, is the nearest of all whose distance we know.
You have heard how far the sun is from the earth. The distance of Alpha
Centauri is _two hundred and seventy-five thousand times as much_. Can
you picture to yourself that vast reach of space--a line ninety-three
millions of miles long, repeated over and over again two hundred and
seventy-five thousand times?
But Alpha Centauri is one of the very nearest. The brilliant Sirius is
at least twice as far away. Others utterly refuse to show the smallest
change of position. It is with them, as had been said, much the same as
if a man were to look at a church-steeple, twenty miles distant, out
of one pane in a window, and then were to look at it out of the next
pane. With the utmost attention he would find no change of position in
the steeple. And like the base-line of two glass panes to that steeple,
so is the base-line formed by our whole yearly journey to thousands
of distant stars. We _might_ measure how far away they are, only the
longest base-line within our reach is too short for our purpose.
The planet Neptune has a wider orbit than ours. But even his orbit,
seen from the greater number of the stars, would shrink to a single
point. After all, how useless to talk of two hundred and seventy-five
thousand times ninety-three millions of miles! What does it mean? We
can not grasp the thought.
Let us look at the matter from another view. Do you know how fast light
travels--this bright light shining round us all day long? Light, so far
as we know, does not exist everywhere. It travels to and fro, from the
sun to his planets, from the planets to one another; from the sun to
the moon, from the moon to the earth, and from the earth to the moon
again.
Light takes time to travel. This sounds singular, but it is true. Light
can not pass from place to place in no time. Light, journeying through
space, is invisible. Only when it strikes upon something, whether a
solid body or water or air, does it become visible to our eyes. The
shining all round us in the day-time is caused by the sunlight being
reflected, not only from the ground, but from each separate particle
of air. If we had no atmosphere, we should see still the bright rays
falling on the ground, but the sky above would be black. Yet that black
sky would be full of millions of light-rays, journeying hither and
thither from sun and stars, invisible except where they alight upon
something.
The speed of light is far beyond that of an express train, far beyond
that of the swiftest planet. In one tick of the clock, Mercury has
rushed onward twenty-nine miles. In one tick of the clock, storm-flames
upon the surface of the sun will sweep over two or three hundred miles.
But in one tick of the clock a ray of light flashes through one hundred
and eighty-six thousand three hundred and thirty-seven miles.
One hundred and eighty-six thousand miles! That is the same as to say
that, during one single instant, a ray of light can journey a distance
equal to about eight times round and round our whole earth at the
Equator.
By using this wonderful light-speed as a measurement, we gain clearer
ideas about the distances of the stars. A ray of light takes more
than eight minutes to pass from the sun to the earth. Look at your
watch, and note the exact time. See the hand moving slowly through the
minutes, and imagine one single ray of light, which has left the sun
when first you looked, flashing onward and onward through space, one
hundred and eighty-six thousand miles each second. Eight minutes and a
half are over. The ray falls upon your hand. In those few minutes it
has journeyed ninety-three millions of miles.
So much for the sun’s distance. How about the stars? Alpha Centauri,
a bright star seen in the southern hemisphere, is one of our nearest
neighbors. Yet each light-gleam which reaches the eye of man from that
star, left Alpha Centauri four years and a third before. During four
years and a third, from the moment when first it quitted the surface
of the blazing sun, it has flashed ceaselessly onward, one hundred and
eighty-six thousand miles each second, dwindling down with its bright
companion-rays from a glare of brilliancy to a slender glimmer of light
till it reaches the eye of man. Four years and a third sounds much,
side by side with the eight minutes’ journey from the sun. Sound would
take more than three millions of years to cross the same abyss. At
the constant velocity of thirty-seven miles an hour, an express-train
starting from the sun Alpha Centauri would not reach the earth until
after an uninterrupted course of nearly seventy-five millions of years.
This is our _neighbor_ star. The second, the nearest after it, is
nearly double as far, and is found in quite another region of space, in
the constellation of Cygnus, the Swan, always visible in our northern
hemisphere. If we wish to understand the relative situation of our sun
and the nearest two, let us take a celestial globe, and draw a plane
through the center of the globe and through Alpha Centauri and 61
Cygni. We shall thus have before us the relation which exists between
our position in infinitude and those of these two suns. The angular
distance which separates them on the celestial sphere is 125°. Let
us make this drawing, and we shall discover certain rather curious
particulars. In the first place, these two nearest stars are in the
plane of the Milky Way, so that we can also represent the Milky Way on
our drawing; again, this celestial river is divided into two branches,
precisely in the positions occupied by these two nearest stars, the
division remaining marked along the whole interval which separates
them. This drawing shows us, further, that if we wish to trace the
curve of the Milky Way with reference to the distance of our two stars,
it will be nearer to us in the constellation of the Centaur than in
that of the Swan; and, in fact, it is probable that the stars of that
region of the sky are nearer than those of the opposite region. Another
very curious fact is, that both the nearest stars are double.
But look at Sirius, that beautiful star so familiar to us all. The
light which reaches you to-night, left his surface from nine to ten
years ago. Look at the Little Bear, with the Pole-star shining at the
end of his tail. That ray of soft light quitted the Pole-star some
forty years ago. Almost half a century it has been speeding onward and
ever onward, with ceaseless rapidity, till its vast journey is so far
accomplished that it has reached the earth. Look at Capella, another
fair star of the first magnitude. The light which reaches you from her
has taken over thirty years to perform its voyage. Ten, thirty, forty
years--at the rate of 186,000 miles per second!
These stars are among the few whose distance can be roughly measured.
Others lie at incalculable distances beyond. There are stars whose
light must, it is believed, have started hundreds or even thousands of
years before the soft, faint ray at length reaches the astronomer’s
upturned eye through the telescope.
Look at Capella, how gently and steadily she shines! You see Capella,
not as she is _now_, but as she _was_ thirty years ago. Capella may
have ceased to exist meantime. The fires of that mighty sun may have
gone out. If so, we shall by and by learn the fact--more than thirty
years after it happened. Look at the Pole-star. Is there any Pole-star
now? I can not tell you. I only know there _was_ one, forty years ago,
when that ray of light started on its long journey. Stars have ceased
to shine before now. What may have happened in those forty years, who
can say? Look at that dim star, shining through a powerful telescope
with faint and glimmering light. We are told that in all probability
the tiny ray left its home long before the time of Adam.
There is a strange solemnity in the thought. Hundreds of years
ago--thousands of years ago--some say, even tens or hundreds of
thousands of years ago! It carries us out of the little present into
the unknown ages of a past eternity.
If the neighboring stars are placed at tens and hundreds of trillions
of miles from us, it is at quadrillions, at quintillions of miles
that most of the stars lie which are visible in the sky in telescopic
fields. What suns! what splendors! Their light comes from such
distances! And it is these distant suns which human pride would like
to make revolve round our atom; and it was for our eyes that ancient
theology declared these lights, invisible without a telescope, were
created! No contemplation expands the thought, elevates the mind, and
spreads the wings of the soul like that of the sidereal immensities
illuminated by the suns of infinitude. We are already learning that
there is in the stellar world a diversity no less great than that
which we noticed in the planetary world. As in our own Solar System
the globes already studied range from 6 miles in diameter (satellites
of Mars) up to 88,000 miles (Jupiter)--that is to say, in the
proportion of 1 to 14,000--so in the sidereal system the suns present
the most enormous differences of volume and brightness: 61 Cygni, the
stars numbered 2,398 in the catalogue of Lalande, and 9,352 in the
catalogue of Lacaille, and others of the eighth or ninth magnitude, are
incomparably smaller or less luminous than Sirius, Arcturus, Capella,
Canopus, Rigel, and the other brilliants of the firmament.