CHAPTER XXI.. Star-Groups.

STAR-GROUPS.

The names of different Star-Groups are very old indeed. On a map or globe of the heavens you may see them pictured, with the figure of an animal or a man from which the name of the Constellation is taken.

These figures were no doubt a help, in very early times, when people wished to learn the different stars; though the star-groups can hardly be said to bear any real likeness to the figures.

As we journey round the Sun, month by month, we see him against different Star-groups in the heavens--against one constellation after another.

Actually, of course, we do not see the Sun against the stars, since all stars beyond the Sun are hidden by his brightness. But we see at night those stars which lie in the opposite direction, and we know each month, without seeing, which group lies exactly behind the Sun.

Suppose you are in a room with a lighted lamp on a table in the middle. And suppose you walk slowly round the table.

As you go you will see the lamp against different parts of the room in turn. First, perhaps, against a window, then against a wall, then against a fireplace, then against a door, then against another wall, then against a sideboard or chiffonier, and so on.

The lamp itself does not stir; but you, by moving onward, change its background and give it a sort of “seeming pathway” round the room. If it were very far away, instead of very close, it might really appear to you to be moving.

This is how we see the Sun seem to travel among the different star-groups. He does not go any nearer to the stars than usual; he only comes between them and us. In fact he does not really go or come; but as we move on we make him lie between us and one star-group after another.

Twelve constellations are behind this seeming pathway of the Sun, and they are called “The Signs of the Zodiac.” It would be a good plan to learn them by heart some day. Here are the names of the twelve star-groups in English and in Latin:

The Ram Aries. The Bull Taurus. The Twins Gemini. The Crab Cancer. The Lion Leo. The Virgin Virgo. The Scales Libra. The Scorpion Scorpio. The Archer Sagittarius. The Goat Capricornus. The Water-carrier Aquarius. The Fishes Pisces.

In all these twelve groups we find only five stars of the first magnitude.

Besides those particular star-groups which lie behind the Sun as we journey there are many other constellations in all parts of the sky.

Certain stars in the southern half of the heavens can be seen by people living on the northern half of our Earth. And certain stars in the northern half of the heavens can be seen by people living on the southern half of our Earth.

But the very far north stars, lying over, or very nearly over, our north pole, are never seen at all in the far south of the Earth. And the very south stars, lying over, or very nearly over, our south pole, are never seen at all in the far north of the Earth.

People living, for instance, in South Australia cannot get a glimpse of the Pole-star or the Great Bear; and people living in England or in New England cannot get a glimpse of the Southern Cross.

Remember that, either way, whether from the north pole or from the south pole of the Earth, a man always looks up into the sky. The heavens are always upward. The sky above the south pole is no more downward than the sky above the north pole. All the “downward” of which we know is towards the centre or middle of our Earth.

Nobody now need sit looking up at the sky and saying,

“Twinkle, twinkle, little star; How I wonder what you are!”

for we know what the stars are.

I do not mean for a moment that we know all about them, or that we have not an immense amount still to learn. But we do certainly know what they are. They are Suns.

The twinkling is not a part of the stars themselves. It is brought about by the way in which the little rays of star-light travel through our air. If we could get away from the Earth, right outside the air, we should then see the stars to shine steadily, without any twinkling.

Jupiter and Venus and other planets do not twinkle when we look upon them. You may usually know a planet from a star by its not twinkling.

No planet can ever be seen by us, even through the very biggest of telescopes, at such an enormous distance as that of the nearest star. For the planets shine by borrowed light, as our Moon shines; and you know how dim moonlight is, compared with sunlight. Only a sun, shining with the brilliance of its own great heat, can possibly be seen so very, very far away.

Any number of worlds may be there: cooled worlds, like our Earth; half-cooled worlds, like Jupiter and Saturn--such worlds journeying round distant stars as the planets of the Solar System journey round our Sun. Only if they are there we cannot know it; our eyes cannot make them out.

Suppose you and I could go for a long, long journey through the skies, straight from our Earth away to the star Alpha Centauri. That is the nearest star in all the heavens of which we yet know.

Alpha Centauri is a very bright star, one of the First Magnitude. But you cannot see it in our northern skies. You would have to go much farther south to get a sight of Alpha Centauri.

Suppose that we were to start on this vast journey, taking with us the great Lick telescope of California. And suppose that all the way we never once looked back in this direction until we reached the neighborhood of that bright star--until we got near enough to see Alpha Centauri as a large radiant Sun.

Then suppose that we turned round and gazed through the big telescope towards this little Earth left so far behind.

What do you think we should see?

No Earth at all! No Moon! No Jupiter, no Venus, no Mars, no planets! No great, warm, glowing Sun! Only one little faint distant star sending forth its feeble glimmer!

All else would have vanished utterly. At the distance of the nearest star, nobody, looking in this direction, with man’s eyes and with such telescopes as we have on Earth, could find out anything at all about the Solar System. All the worlds and their moons would be hidden. The very most that anyone could see would be our Sun, as one tiny star.

Just so we on the Earth gaze at the far-off stars; and we see them shining as lonely suns with no worlds travelling round them. Yet they may not be lonely. Any one of those stars may have its own great kingdom of worlds. Any number of planets may be there. Who can tell? We are not able to know, because the gentle shining of borrowed or reflected light cannot possibly reach to such a distance. The most that we have any right to say is that we are not able to see any worlds belonging to the stars.

QUESTIONS.

1. What is meant by the Signs of the Zodiac?

The twelve constellations against which in turn the Sun is seen in the course of a year.

2. How is the Sun seen against these constellations?

In consequence of our Earth’s yearly journey round the Sun.

3. Do we actually see the stars beyond the Sun?

No; for all stars in the same direction as the Sun are hidden by his brightness.

4. Tell me the names of the twelve constellations.

Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, Pisces.

5. How many very bright stars are in those constellations?

Five stars of the first magnitude.

6. Can all stars in the sky be seen from all parts of the Earth?

No. Some stars to the far north are never seen in the far south; and some stars to the far south are never seen in the far north.

7. Tell me of a constellation never seen from Australia.

The Great Bear.

8. Tell me of a star-group never seen from New England.

The Southern Cross.

9. What are Stars?

Stars are Suns.

10. Why do Stars twinkle?

Only because of the way in which their light travels through our air.

11. Tell me of one way by which we may know planets from stars?

A star generally twinkles; and a planet generally does not twinkle.

12. Do any planets belong to the distant stars?

Any of the stars may have worlds belonging to them, but we cannot see such worlds.

13. Why cannot we see them?

Because the distance is too great.

14. Why should we see a star if we cannot see a planet at that distance?

A star shines by its own light. A planet shines only by reflected light, therefore much more dimly.

15. If we could journey to the nearest known star, how much should we see of the Solar System?

No planets nor moon at all: nothing but the Sun as one dim star.