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About three hundred years ago, there lived a wise man, named Galileo, who spent his nights in watching the stars, and in considering how they moved. Perhaps you think the stars are little shining lamps, lit up in the sky every night, which do not move at all. Galileo knew better; and, in his long night-watches, he found out some wonderful things about our world which you shall hear. Not that he was exactly the first to make these discoveries. But Galileo was among the first who wished to make others as wise as himself. He wrote his wonderful secrets in a book and taught the people. Alas, his books were burned, and he, himself, was imprisoned. Men said his strange tales were not true, and were angry with the man who wished to teach them.

Have you noticed that things look smaller and smaller the farther you are from them? That a kite flies up, till it looks like a speck; that a man in the distance looks no bigger than a child? Get far enough off, and the very largest thing looks no bigger than a dot. Even our own great world would seem no larger than one of the stars in the sky if we could get far enough off to see it so small; which we never can, because we cannot get out of our own world.

Galileo's wonderful discovery was, that nearly all the stars we see in the sky are as large, some of them many times as large, as our world. They are so far off that they look small to us, just as our world would look if seen from a star.

Then he went on to tell that our world is really a kind of star, which, with seven others something like it, is always going around the sun. These eight stars, which are always wandering around the sun, are called planets, a word which means wanderers. Our world is a planet, and its name is Earth; another planet is called Venus; and each of the other planets has a name of its own which you may learn some day.

But, you say, the stars all shine like lamps; how then can our Earth look like a star? It is not on fire. It is true that most of the stars do shine and burn like the sun, but these eight planets, of which our Earth is one, shine in another way. Have you ever seen the windows of a house look red and bright when the sun was shining on them in the evening? Sometimes you would think the house was on fire, they look in such a blaze; but it is only the light of the sun which they are sending back, or reflecting. On a sun-shiny, hot day by the sea-side you can hardly bear to look at any thing. Water and houses and pavement dazzle you so with the sun's light, which they are reflecting, that it is almost as bad as trying to look at the sun himself.

If we were off our Earth, far, far away, up in space, we should not see houses, trees, and water, but just a ball shining all over with the light of the sun, which it is giving back or reflecting. And that is how it is that these eight planets, and our moon also, shine like bright stars, though they are not really bright themselves. They send back, or reflect, the bright light of the sun.

Notebook Work: Write the answers to the questions.

1. Why did people burn Galileo's books and imprison him?

2. Does an object look larger or smaller as you move farther from it?

3. Up close, are the stars in the night sky tiny like marbles or large like our Earth?

4. Why do planets shine like stars from space? Do they glow with their own light, like our sun, or do they merely reflect light?

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