GIANT-SUNS AND CLUSTERS.
All stars do not shine alike. They are different in brightness,
different in size, different in speed.
There are brilliant suns and dim suns, great suns and little suns,
fast suns and slow suns, in the universe of stars, just as there are
brilliant worlds and dim worlds, great worlds and little worlds, fast
worlds and slow worlds, in our Solar System.
But the brightest star is not always truly the biggest star; just as
the brightest planet in our sky is by no means always the largest world.
You know how bright Venus is--a good deal brighter than Jupiter. Yet
Venus is far, far smaller than Jupiter. Venus is brighter because she
is so much the nearer of the two, not at all because of greater size.
The very brightest star in our whole sky is SIRIUS. Yet you must not
suppose that Sirius is larger in himself than any other star. He is
brighter partly because he is so much _nearer_ than most other stars.
I do not mean to say that Sirius is what one would call a very near
star, if such a word can be used about any single star in the sky.
Alpha Centauri, though the nearest of which we know, is not really
near; and Sirius is perhaps nearly twice as far off as Alpha. That,
however, is not much, compared with the enormous distances of many
stars.
Sirius is no doubt a splendid Sun, most likely larger and brighter than
our Sun. But our Sun is not so very particularly large as a star among
stars. He is only large as a Sun among little worlds. Sirius may very
well be bigger than our Sun and yet be by no means one of the biggest
stars in the sky.
No one has yet been able to measure the actual size of Sirius, because
he always looks to us like one point of light. But we know about how
far off he is, and we know that our Sun at that same distance would not
be so bright a star as Sirius is. This looks as though Sirius were the
larger Sun of the two, only without any very startling difference.
Matters are otherwise when we turn to ARCTURUS.
Sirius is in the southern half of the heavens, and Arcturus is perhaps
the very brightest star in all the northern half of the heavens, though
a good way behind Sirius in radiance.
Arcturus seems to be a truly wonderful Sun. He is eleven millions of
times farther away from us than our Sun is. Imagine what this means!
If you had a rope 92 millions of miles long, reaching from our Earth to
the Sun, you would need _eleven millions_ of such ropes, joined end to
end, to reach from the Earth to Arcturus!
If our Sun were moved to where Arcturus is we should see him only as a
very dim star indeed. But Arcturus is one of the most brilliant stars
in our sky.
This seems to show that he must be an enormous Sun: a very giant among
giants; so huge that our great Sun would perhaps be but as a little
ball by his side.
Capella, one of our most beautiful northern stars, is believed to
be another giant Sun. Our Sun, at the distance of Capella, would be
only just visible without a telescope, while Capella is almost, if
not quite, as bright as Arcturus. Since the radiance of Capella is
certainly not caused by nearness it is most likely caused by great size.
So, although Sirius may be to us “the monarch of the starry skies,” he
is monarch only in appearance. He is brightest because he is one of
the nearer stars, not because he is really one of the very largest.
Arcturus, Capella, and others also, are believed far to surpass him in
size.
In this little book I must not even try to tell you many of the wonders
of the starry heavens. If you wish to learn more you will by-and-by
read in other books about the many-colored suns which are seen in
telescopes, and the pairs of suns which journey through the skies in
company.[3]
[3] See “Sun, Moon and Stars,” pp. 283-286.
You will read also about the curious changeable stars, which get
bright and dim by turns; and about the extraordinary New Stars, which
sometimes appear and last for a while, and then vanish again.[4]
[4] Ibid. pp. 279-282.
I am only going to tell you now a very little about Star-Clusters and
Nebulæ.
A Star-Cluster is just what its name says it is--a Cluster of Stars
very near together. Near, as seen by us at this distance; not always
really near.
A great many star-clusters are known, and some can be seen without a
telescope, while others are mere specks even in a fairly good telescope.
In some clusters only about one or two hundred stars are seen. In
others we find a countless multitude of stars--thousands of suns
seemingly packed together in a mass.
The _packed_ look comes from great distance. If we were near enough
we should see the suns of such a cluster to be well apart--perhaps
even very widely separated. You know how the trees of a forest,
which close at hand stand apart, seem in the distance to shrink close
together. That is how the stars do.
[Illustration: _The Nebula in Andromeda._]
One very important cluster you may easily see any clear winter
evening--the cluster of the Pleiades. Most people can make out five or
six dim stars; and through a mere opera-glass a hundred may be counted.
The word “nebula” means “a cloud.” _Nebulæ_ is the plural, meaning
_clouds_.
But the Nebulæ are not fleeting and watery clouds, like our
Earth-clouds. They are pale patches of light in the sky, fixed as the
stars themselves--in one spot century after century.
Only two or three of the nebulæ can be seen without a telescope. The
brightest of them all is a faint patch in the star-group Andromeda; and
the next brightest is “The Great Nebulæ” in the constellation Orion.
Photographs are now taken of the nebula, and we thus see more of their
true shapes than could ever be found out by simply gazing at them with
our own eyes, which so soon get tired.
It used once to be thought that a Nebula was only a very, very far off
star-cluster--too far for the largest telescope ever to make us able to
see the little separate star-points.
But it has now been found that many of the nebulæ are not clusters of
stars at all; they are made of shining gases.
Gases out there in the distant sky, it is supposed, do not burn away,
like gas here on the Earth, because in the sky, far off, there is no
air, and nothing can _burn away_ without air. Only when the great
masses of gas are very hot they shine with their own heat; and instead
of burning away they go on shining, year after year. That is how we see
them.
Some nebulæ are made partly of gases and partly of stars. And some
star-clusters have a good deal of shining gas round about the stars.
For a long while nobody knew that there was any bright gas round the
stars of the Pleiades cluster. But lately, in some photographs taken
of the Pleiades, a curious soft haze has come out round several of the
stars, as you may see for yourself in a photograph which tells a truer
tale than our eyes can tell.
Do you remember hearing that a star is, most likely, a young world not
yet cooled? Well, it _may_ be that a nebula is a young sun, or cluster
of suns, not yet shaped.
These things we cannot know with certainty. We can only say what is
believed to be most likely the right explanation.
[Illustration: _The Great Nebula in Orion._]
Perhaps you have sometimes noticed across the sky at night a band of
pale light, wider here, narrower there.
In a clear evening, after dark, it may always be seen, and it is called
THE MILKY WAY.
Stars lie scattered over and around the Milky Way. But beyond and
behind all the brighter stars is spread that soft pale band, which
in itself is made up of stars--multitudes upon multitudes of distant
suns. They are either so very distant or so very small, or perhaps both
together, that we cannot see them as separate stars. We only see the
general shining of them all.
Through a telescope great numbers of stars can be seen in the Milky
Way, yet still the band of hazy light always lies beyond.
The Milky Way belongs to the same vast Universe of Stars to which our
Sun belongs. Indeed, our Sun, with all his planets, is actually _in_
the Milky Way.
When you are looking up into the sky, trying to learn about the
countless suns of the great Universe, never forget one thing--that “our
Father in Heaven” has made them all, and is KING over them all.
If we see a lovely picture, or a beautiful building, we naturally want
to know more about the man who painted the picture or planned the
building.
Then surely, while searching into the grand distances and glory of
the skies, we ought to lift our thoughts in reverent adoration to our
Father in Heaven, and to the Son of God, by whom “were all things
created that are in heaven and that are in earth.” For “_without Him
was not anything made that was made_!”
QUESTIONS.
1. Are stars all of the same size?
No; some are large and some are small.
2. Are the brightest stars always the largest in size?
Not at all. A star may be brighter than another only because it is much
nearer.
3. Which is the brightest star in our heavens?
Sirius, the Dog-star.
4. Is Sirius as bright as Venus?
No; but Venus is a planet, not a star.
5. Is Sirius one of the very largest stars?
Sirius is perhaps bigger than our Sun, but not one of the biggest stars.
6. Why, then, is Sirius the brightest?
Sirius is one of the nearer stars; not actually near, but far nearer
than many others.
7. Is our Sun one of the biggest stars?
No; only a moderate-sized star.
8. Tell the names of two giant suns.
Arcturus and Capella.
9. Why do we believe Arcturus and Capella to be larger than Sirius?
Because they are both very bright stars; and yet they are very much
farther away than Sirius.
10. What are Star-Clusters?
Clusters of hundreds or thousands of suns, so distant as to seem to us
quite close together.
11. What are Nebulæ?
Hazy clouds like patches in the sky.
12. What are Nebulæ made of?
Some are only great masses of shining gas. Sometimes they are made of
stars and gases together.
13. Which are the two brightest Nebulæ?
The Nebula in Andromeda and the Nebula in Orion.
14. Tell me the name of a well-known Star-Cluster easily seen?
The Pleiades.
15. What do we learn from a photograph of the Pleiades?
That some of the stars of this cluster have nebula-gas round them.