CHAPTER XXII.. Giant-Suns and Clusters.

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.

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.

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.

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.

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.