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The sun, the moon and the stars are all in the sky. We can see the moon and the stars at night.
The sun is like a ball. It is much bigger than the moon. It gives us heat. The sun has "family". The family contains(包含，包括) the sun and a group of planets(行星).
The moon is like a ball, too, like the sun and the earth. Sometimes it looks as round as a plate. Sometimes it looks like half a plate. It looks bigger when it is much nearer to the earth. But it is much smaller than the sun. It is smaller than the stars. The light of the moon comes from the sun. It has no light of its own.
The stars look smaller than the sun and the moon. But most of the stars are bigger than the sun. They look small because they are very far away from us. The stars are in the sky all day. But the light from the sun is too bright, so we can't see the stars in the day.