The universe (宇宙) is so wide that we still don’t know much about it. It     1     the earth, the sun, the moon and the stars, and the space between them as well. Many of the stars can not be     2     because they are too far away. The moon travels around the earth. It’s our satellite. It’s the     3     to our earth. So far, humans have visited it already. And spaceships without people have reached other parts of the universe. Many countries have launched lots of man-made satellites into space. The satellites travel around the earth and help us     4     more about the earth, the weather and other things. They are used for     5     messages. With their help, TV and radio programs can be sent to countries all over the world. Satellites can also help us make telephone calls to foreign countries.

Our knowledge of the universe has been growing all the time.     6     space satellites (人造卫星), the world itself is becoming a much     7     place and people from different countries now understand each other better.

The universe is very big. But how large is the universe? It is impossible     1     how large the universe is.

But we know the earth is our home. It is a planet and it     2     around the sun. The moon goes around the earth. There are seven other planets go around the sun. The sun and its planets are a system     3     the solar system. So far, some astronauts     4     to the moon. Some scientists     5     many spaceships to some other planets. But we haven’t     6     life on other planets, because none of them     7     an environment like the earth.

Scientists have also found many other galaxies in the universe. But they are very far away, so no spaceship has travelled far enough     8     them. Is there any life out of the solar system? Have there been visitors to the earth from other planets? I think there is still a long way     9     to know that. When I grow up, I     10     an astronaut and work for China’s space station.

Scientists think that there has been life on the earth for hundreds of millions of years. However, we haven’t     1     life on any other planets yet.

The earth is a planet and it     2     around the sun. Seven other planets also go around the sun. None of them has an environment like that of the earth, so scientists do not     3     they will find life on them. The sun and its planets are called the solar system, and our solar system is a small part of a much larger group of stars and planets,     4     the Galaxy or the Milky Way. There     5     billions of stars in the Galaxy, and our sun is only one of them.

Scientists     6     many other galaxies in the universe already. They are very far away and their light     7     to travel for many years to reach us. So how large is the universe? It is impossible to imagine.

Scientists have sent spaceships to the planet Mars to take photos. They have even sent spaceships to travel outside the solar system . However, no spaceship has travelled far enough     8     other stars in our Galaxy. Scientists have always asked the questions: With so many stars in the universe, are we alone or is there life in space? Have there been visitors to the earth from other planets? Why has no one     9     with us? We     10     the answers yet.