In the universe,as we all know,there is the sun,the moon,the earth and a good manystars.Through our geography lessons,we know the earth goes around the sun,and the moon goes around the earth.We have day and night because the earth keeps turning all the time.When our part of the earth turns to the sun,it is day.When our part of the earth turns away from the sun,it is night. Just because the moon is closer to the earth than the sun, it looks much bigger than the sun. Big things will look smaller when they are further, and small things also look bigger when they are nearer. The sun is big enough to give out very strong light. The moon can't give any light at all, but it looks quite bright, too. Why? In fact, the light from the moon comes from the sun. The moon looks much bigger and brighter than the stars. But actually   the stars are much bigger and brighter than the moon.They look smaller than the moon also because they are further away from the earth. There are many other planets in the universe. But of all the planets, only on the earth there are living things and people can only live on the earth, too. But at 9:00 a.m. on October 15th,2003, Chinese pilot Yang Liwei was sent up to space. He stayed there for 21 hours.It was the first time for Chinese to get into space. People and living things can live on the  _  .
earth Mars moon sun