In the universe, there is the sun, the moon, the earth and many stars. Through our geography lessons, we know the earth goes around 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. The other part of the earth is always contrary.

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 further, and small things also look bigger when they are nearer.

The sun is big enough to give out very strong light. The moon can’t give 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 in fact, the stars are much bigger and brighter than the moon. They look smaller than the moon also because they are further away from the earth.

Earth is so important because living things and people can only live on the earth. And some countries have sent astronauts to the space to learn more about the universe. At 9:00 a.m. on October 15th, 2003, Chinese astronaut Yang Liwei was sent up to space. He stayed there for 21 hours. It was the first time for Chinese to get into space.

Some people believe that humans could live on the planet Mars by the year 2100. Our own planet, the Earth, is becoming more and more crowded and polluted. It is hoped that people could start again and build a better world on Mars. Here is what life there could be like.

At present, our spacecraft are too slow to carry large numbers of passengers (乘客) to Mars and it would take months. With the development of technology, by the year 2100, the journey might only take about 20 minutes in spacecraft that travel at the speed (速度) of light! However, the spacecraft would travel really fast, so the journey to Mars might be quite uncomfortable. Many people would feel ill.

Humans can’t live without water, air or food. So far, nobody knows if there would be enough water or air on Mars for people. Moreover, scientists are not sure if plants could grow on Mars. Food would most probably be made like pills (药片) and would not keep long.

Compared with life on the earth, life on Mars would be better in some ways. People would have more space. They might live in houses with huge comfortable rooms. Also, robots would do lots of their work so that they could have more time to relax. There would probably be no schools. Every student would study at online schools with “e-teachers”.

Life on Mars would be interesting and challenging (充满挑战的). However, it may take hundreds of years to make it true. So the most important thing we need to do now is to protect our beautiful blue planet-the Earth!

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

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

The harm of the radiation won’t be found until their children even grandchildren are born. Some special medicine may work a little, but no really effective medicine has been found so far.

Space rubbish 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 spaceships, and the rest are space rubbish. An explosion (爆炸) in space in 1999 made a cloud of 300, 000 fragment (碎片), each at least 4mm in size. A small piece of these even knocked a spaceship window and caused some damage (损坏).

Scientists are watching and reporting any possible danger all the time. They are working to deal with space rubbish. Although space is really dangerous, it interests many people on the earth.

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.