In the universe, as we all know, there is the sun, the moon, the earth and many stars. 【小题1】 our geography lessons, we know the earth 【小题2】 around the sun, and the moon goes around the earth. We have day and night 【小题3】 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 【小题4】.

Just because the moon is 【小题5】 to the earth than the sun, it looks much bigger than the sun. Big things look smaller when they are further, and small things also look bigger when they are nearer. The sun is big 【小题6】 to give out very strong light. The moon 【小题7】 give any light at all, but it looks quite bright, too. Why? In fact, the light from the moon comes from the 【小题8】. 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’re further away from 【小题9】 earth than the moon.

There are many 【小题10】 planets in the universe. But of all the planets, there are living things only on the earth and people can only live on the earth too.

Scientists think that 【小题1】 has been life on earth for 【小题2】 (million) of years. However, we haven’t found life on other planets yet. The earth is a planet and 【小题3】 goes around the sun. And there are seven other planets that also go around the sun. The sun and its planets are 【小题4】 (call) the solar system. The solar system is 【小题5】 small part of the universe.

Scientists have launched many spaceships to 【小题6】 [ɪkˈsplɔː(r)] other planets in the solar system. Some spaceships have gone 【小题7】 [bɪˈjɒnd] the solar system. However, no one 【小题8】 discovered any life in space yet.

Why has no one from other planets 【小题9】 ( send) us a message? Have they tried to send 【小题10】   (information) to us? With so many stars in space, are we alone, or is there life on other planets in space?

We see the sun every day. If it is 【小题1】（sun）, we can see the moon at night, too. The moon is near us. So far astronauts 【小题2】（visit） the moon several times. The moon is almost 【小题3】 nearest satellite（卫星） to the earth in space.

Light 【小题4】（travel）at 300,000 kilometers a second. Light reaches us from the moon in less than a second and a half. The moon is about 382,000 kilometers away.

Light from the sun arrives in the earth in about 8.5 【小题5】（minute）. The sun is about 149,640,000 kilometers away 【小题6】 the earth. Other stars are much 【小题7】（far） away than the sun. Light from the nearest star reaches 【小题8】（we）in about four years. When you look at a star, it is very small. 【小题9】 in fact many of them are much bigger than the sun. They look small only because they are 【小题10】（real） far away.