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.

Lots of scientists believe that there’s life on other planets. Because of this, they keep doing research about the universe. They have sent astronauts to the moon. And they have     1     the answer. There’s no life on the moon. Not long ago they     2     spaceships to Mars. There, they didn’t find life, either. And they found the environment of Mars was     3     from that of the earth. Then they knew it was     4     for people to live on Mars.

    5     they haven’t received a message from other planets, they believe that their idea is right. Recently they have     6     a planet. It’s     7     Proxima Centauri. It’s very     8     to our earth. It is just over four light years away. Proxima Centauri is     9     than the earth. And there’s water on this planet. It     10     mean that life is possible there. Now scientists are studying this planet. Soon they will tell people the answer.

From a plane you can see the fields,     1    , mountains or rivers below. If we go into space, we see more and more of the earth. People and man-made satellites are     2     out into space to look at the earth, the stars and other     3     and learn more about them.

The moon is our     4     neighbour in space. It is our satellite and men have visited it already. It is smaller than the earth.     5     can’t grow on the moon because there’s no air or water on it.

The moon hasn’t its own light. It     6     back the light of the sun. When the sun is shining on the side of the moon that faces us, it     7     like a great round ball. We can’t see the moon when the sun is shining on the side of the moon that faces away from     8    .

In fact the moon isn’t as near as it looks. It is three     9     and eighty thousand kilometres away from the earth. Of course we can fly to the moon in a spaceship. A spaceship     10     very, very fast, and it flies at about eleven kilometres a second. So it only takes more than three days to get there by spaceship.

Lots of scientists believe there’s life on other planets. Because of this, they keep doing research     1     the universe. They have sent astronauts to the moon. And they have     2     the answer. There’s no life on the moon. Not long ago they     3     spaceships to Mars. There, they didn’t find life. And they found the environment of Mars was     4     from that of the earth. Then they knew it was     5     for people to live on Mars.

    6     they haven’t received a message from other planets, they believe their idea is right. Recently they have discovered a planet. It’s     7     Proxima Centauri (比邻星). It’s very     8     to our earth. It is just over four light years away. Proxima Centauri is     9     than the earth. And there’s water on this planet. That     10     mean that life is possible there. Now scientists are studying this planet. Soon they will tell people the answer.

Lots of scientists believe that there’s life on other planets. Because of this, they keep doing research about the universe. They have sent astronauts to the moon. And they have     1    the answer. There’s no life on the moon. Not long ago they     2     spaceships to Mars. There, they didn’t find life, either. And they found the environment of Mars was     3     from that of the earth. Then they knew it was     4     for people to live on Mars.

    5     they haven’t received a message from other planets, they believe that their idea is right. Recently they have     6     a planet. It’s     7     Proxima Centauri. It’s very     8     to our earth. It is just over four light years away. Proxima Centauri is     9     than the earth. And there’s water on this planet. It     10     mean that life is possible there. Now scientists are studying this planet. Soon they will tell people the answer.

Scientists have always wanted to know more about the other worlds in space. Years ago they knew a lot about the moon. They knew how big it was and how far it was     1     the earth. But they wanted to know more about it. They thought and thought. At last they found the only way to know more was to send men to the moon.

The moon is about 384,000 kilometers     2     from the earth. A plane can not fly to the moon because the air reaches only 240 kilometers high above the earth. Then there is no air. But there’s something that can fly even     3     there is no air. That is a rocket. Rockets can fly out     4     space. Rockets with men in them have already reached the moon. Some rockets     5     men in them have flown to other parts much farther than the moon in the universe. One day rockets may be able to go to any place.

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.

What do you know about Mars? What does it look like?

Mars is the     1     planet from the sun in our solar system and     2     after Mars, the Roman god of war. Its diameter is 53% as     3     as that of the earth. Mars gets around the sun     4     a distance of about 228 million kilometers. You can tell which planet is Mars because it is bright red in the night sky. It looks like a red     5     orange ball. It’s very beautiful. But during spring and summer, the surface of Mars is covered by strong storms. The gravity on the surface of Mars is about two-fifths as strong as it is on earth. So a person     6     weighs 90 kilos on earth weighs only 36 kilos on Mars. The     7     on Mars is between -138℃ and 28℃. The air     8     only 0.13% oxygen.

It takes a spaceship about eight months     9     Mars from the earth when the two     10     are closest to each other. Scientists are still searching for more information about Mars.

The planet Mars is the     1     and most similar planet to Earth. It is very interesting to     2    . For example, Mars has seasons with     3     weather, but other planets have the same temperatures all year round. Was there life on Mars?   

To find out, scientists need to know if Mars ever had water. In 2004, two robot explores （探测器）, or “rovers”, called Spirit and Opportunity were     4     to look for signs of water. These rovers can drive over rocks and all kinds of rough ground. They can also use cameras and send     5     back to Earth.     6     of all, the two rovers found chemicals and patterns （图文） in the rocks that were probably made by water. Then, they moved to another area and found other rocks which may have been created by water. Now scientists think there was probably water on the planet long ago. Today they are still not sure if there was life on Mars. They     7     need more information to decide. The discoveries of the two rovers answered some old questions, but they also     8     many new ones.

What do you know about Mars? What does it look like?

Mars is the fourth planet from the sun in our solar system and is     1     after Mars, the Roman God of War. Its diameter（直径）is 53% as long as     2     of the earth. Mars goes around the sun at a distance of about 228     3     kilometers. You can     4     which planet is Mars because it is bright red in the night sky. It looks like a red and orange ball. It’s very beautiful. But during spring and summer, the surface of Mars is covered by strong     5    . The gravity on the surface of Mars is about two     6     as strong as it is on earth. So a person who weighs 90 kilos on earth weighs only 36 kilos on Mars. The temperature on Mars is     7     -138°C and 28°C. The air has only 0.13% oxygen.

It     8     a spaceship about eight months to reach Mars from the earth when the two planets are the     9     to each other. Scientists are still     10     for more information about Mars.