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.

The moon is the nearest neighbour in space. It is our satellite (卫星) and men have visited it already. It is smaller than the earth. Plants can’t grow on the moon     1     there is no air or water on it.

The moon doesn’t have its own light. It shines back the light of the sun. When the sun is shining on the side of the moon which faces us, it     2     a great ball. We can’t see the other side of the moon. Because that side never faces the earth.

In fact, the moon isn’t as     3     as it looks. It is three hundred and eighty thousand kilometres away from the earth. Of course we can fly to the moon in a     4    . A spaceship flies very, very fast, and it flies at about eleven kilometres a second. So it only     5     more than three days to get there by spaceship.

Is there intelligent (有智力的) life on other planets? For years, scientists said “no.” or “we don’t know.” But today this is changing. Seth Shostakovitch and Alexandra Barnett are astronomers (天文学家). They believe intelligent life exists (存在)     1     in the universe. They also think we sill soon contact these beings(人；生物).

Why do Shostakovitch and Barnett think intelligent life exists on other planets? The first     2     is time. Scientists believe the universe is about 12 billion years old. “This is     3     enough for other planets to have intelligent life,” says Shostakovitch and Barnett. The second reason is size—the universe is huge. “Tools like the Hubble Telescope (哈勃望远镜) have     4     that there are at least 100 billion galaxies,” says Shostakovitch. “And our galaxy, the Milky Way, has at least 100 billion stars. Some planets going around these stars might be     5     to Earth.”

In the past, it was hard to look for     6     of intelligent life in the universe. But now, powerful telescopes (高倍望远镜) allow scientists to     7     smaller planets—the size of Mars or Earth—in     8     solar systems. These planets might have intelligent life.

Have beings from space already visited Earth? “Probably not,” says Shostakovitch. “It’s a long way away. However, intelligent beings may contact us in other way, such as radio signals (信号). In fact, they may be trying to communicate with us now, but we don’t have the right tools to     9     their messages. However, this is changing. By 2025, we could make contact with other life     10     in our universe and we might help each other.”

As space science develops, man has learned more and more about space. Space is not only     1     but also dangerous. While working in space, spacemen are facing danger as well as success.

Scientists have     2     out that the radiation (辐射) is the greatest danger to spacemen. When     3     are working in space, they are in danger of the radiation from the sun and other stars, which is bad for their health.

Space     4     is also thought to be a great danger to spacemen. It’s reported that there were 9,000 man-made things flying in space. About 30% of these are satellites, 10% are     5     , and the rest are space rubbish. A small     6     of rubbish even knocks a spaceship window and     7     some damage (损坏).

Scientist are watching and reporting any possible danger all the time. They are working to deal     8     space rubbish.     9     space is really dangerous, it interests many people on the earth. In the near future, it may become     10     for people to spend a few days in a space hotel. We may even choose to leave the earth and live in space in a few years. So we should do something to help improve the space environment.

Our earth gets its warmth and light     1    . The sun is a huge blazing（酷热的）ball, a million times     2     the earth. And it is millions of miles away. The earth spins（旋转） round once every 24 hours. It turns to face the sun and spins away every 24 hours.

When our part of the earth looks on to the sun, we see sunlight and we     3    . When our part turns away from the light, we have night.

When our part begins to turn     4     and we see the first sunlight, we call it morning.

When we are facing the sun most directly, it is noon. Then the sun is closest to begin straight（直接地）above us. When we begin to     5     from the sun, we have afternoon, evening and night.

I’m so happy! Tomorrow I’ll be one of the first students to     1    . The spaceship will leave the Earth at 9 a.m.. It’ll take us to the Moon. I can’t wait!

The moon is around 380,000 kilometres from the Earth, so it’ll take us     2     to get there. There’s no gravity in space, so we’ll all be able to float around in the spaceship. We’ll have to tie ourselves to our beds so that we won’t float away in our sleep!     3    , our bodies may get weak, so we’ll have to     4     every day.

When we arrive, I’m going to walk on the Moon. I’ll have to     5     to help me breathe because there is no air on the Moon. I am going to take as many photos as I can, that is, if my camera still works up there.

The moon looks     1     than the stars at night.     2     in fact, it is smaller than any other stars. The moon looks big to us, because it is closer     3     us than any stars. The moon goes around the earth. It makes one trip about four weeks. The moon is a round ball and looks beautiful.

Now people know quite a lot about the moon. There is no air or water on the moon, so there are not     4     trees or animals, or people on it. The moon gets its light (光) from the sun, but some places on the moon are quite dark. It’s very hot on the moon during the day, but it’s very cold at     5    .

The moon     1     around the earth. It is quite near to us in     2    . It is only 380,000 kilometres away and man has     3     visited it. So far, no man has travelled     4     than the moon, but spaceships without people have     5     other planets of the universe.

Many countries have     6     up satellites(卫星) into space.

These satellites go     7     the earth and help us to learn more about the earth, the weather and other things. Many countries use these satellites to send and receive     8    . For example,     9     their help, China can send its TV and radio programmes to other countries. We can also use satellites to     10     us make telephone calls to foreign countries.