In the universe (宇宙), as we know, there is the sun, the moon, the earth and many stars. Through our geography lessons, we know the earth goes round the sun, and the moon goes round 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 farther, and small things also look bigger when they are nearer,

The sun is bright enough to give out very strong light. The moon can’t give out 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 (事实上) the stars are much bigger and brighter than the moon. They look smaller than the moon also because they are farther away from the earth.

There are still many other planets (行星) in the universe. All of them move round the sun. But of all these planets, only on the earth there are living things and people can only live on the earth too. At 9:00 a.m., on October 15th 2003, Chinese pilot (飞行员) Yang Liwei was sent up to space. He stayed there for 21 hours. It was the first time for Chinese to get into space.

We have always been interested in the moon. 2, 000 years ago, people already knew it moves around the earth and where it would be in the sky at different times of the year. At that time, everything about the moon was learned by watching it carefully in the sky.

When scientists could use telescopes to study the moon more closely, their ideas began to change. They could see the moon was made of rocks. Most scientists thought moon rocks would be different from those on the earth. This was because they believed the moon had once been a planet that had been caught in the earth’s gravity (重力) millions of years earlier.

In 1969, moon rocks were finally brought to the earth and studied. Much to their surprise, scientists found that, except for water, the moon and the earth were made of the same things. Once again new ideas were needed for this new information.

After years of study, most scientists now think that the moon was once part of the earth. They believe very early in its history, maybe 4 billion years ago, something about the size of Mars hit the earth. This sent billions of rocks into space around our planet. These rocks slowly joined together and after many years became the moon.

In the future, though our ideas about the moon may change again, we will still be interested in it.