The sun, the moon, the Earth and stars are all in the universe(宇宙).
We can see the sun in the daytime on the Earth. We can see the moon and stars at night on the Earth. The sun is much bigger than the Earth. The Earth is much bigger than the moon.
The moon looks bigger than stars because it is much nearer to the Earth.It's our nearest(最近的)neighbor(邻居)in space.There is no air or water on the moon.Nobody can live there.
Most stars are bigger than the sun. Why do they look small?Because they are very far away.