Mars is the fourth planet from the Sun in the Solar System. Named after the Roman god of war, Mars, it is often described as the “Red Planet”. Mars sometimes can easily be seen from Earth with just our eyes.

Some people believe that humans could live on the planet Mars by the year 2100. At present, however, our space ships are too slow to carry large numbers of passengers to Mars—it would take months. With the development of technology, by the year 2100, the journey might only take about 20 minutes in space ships that travel at the speed of light! However, the space ship would travel so fast that the journey to Mars might be quite uncomfortable. Many people would feel ill.

Humans cannot live without water, oxygen（氧气）or food. So far, nobody knows whether there would be enough water or oxygen on Mars for people there. Besides, scientists are not sure whether plants could grow on Mars. Food would most probably be in the form of pills（药片）and would not be so delicious.

Gravity（重力）could be another problem. The gravity on Mars is only about three-eighths of that on the Earth. People would have to wear shoes that are specially designed to prevent themselves from floating（漂浮）off into space.

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 large comfortable rooms. Also, robots would do most of their work so that they could have more time to relax.

There would probably be no schools on Mars. Every student would have a computer at home connected to an interplanetary（星际间的）network. They would study at online schools with “e-teachers”.

Anyhow, so many problems and challenges are there, but one thing is clear: Life on Mars would be interesting as well as challenging.

Last year I had a trip with my friend, Nancy. The weather was cloudy except for one night. Nancy and I sat in the field and we felt relaxed. We talked about the fantastic trip, looking at the stars. “It’s a pity we don’t know which stars we’re looking at, Jenny,” said Nancy. “I know some of them.” I answered. Nancy felt surprised when I finally finished telling her all the names I knew.

My interest in stars began when I was eight. My aunt took me to a planetarium (天文馆). A guide showed us the groups of stars and told us stories about how they got their names. The stories were wonderful.

Everyone knows we can see the stars better when it’s not cloudy, but lots of people don’t realize that a bright moon also stops us seeing very much. I always look for the Plough (北斗星), because once I see that, I can find the North Star and other stars.

I wanted to learn more about the stars, so I took a course at the club. There are so many lights in the city that we have to go into the countryside to see any stars. I’m planning to make videos about stars in the countryside. I’ll post them online for everyone to watch. My greatest dream is to be an astronaut and I wish I could have space travel.

If you look at the sky one night and see something moving and shining that you have never seen before, it might be a comet (彗星).

A comet sometimes looks like a star. Like a planet, a comet has no light of its own. It shines from the sunlight it reflects (反射). Like the earth, a comet goes round the sun, but on a much longer path (轨道) than the earth travels.

If a comet isn’t a star, what is it then?

Some scientists think that a large part of a comet is water frozen into pieces of ice and mixed with iron and rock dust and perhaps a few big pieces of rock. When sunshine melts (融化) the ice in the comet, great clouds of gas go trailing after it. These clouds, together with the dust, form a long tail.

Many people perhaps have seen a comet. However no one knows how many comets there are. There may be millions of comets, but only a few come close enough for us to see.

An Englishman named Edmund Halley, who lived from 1656 to 1742, found out a lot about the paths that comets take through the sky. Some comets move out of our sight and never come back. Others keep coming back at regular times. A big comet that keeps coming back was named after Halley because he was the one who worked out when it would come back again. Maybe you have ever seen Halley’s Comets because the last time it came close to the sun and the earth was in the year 1986. Then people all over the world were outside at night to look at it. You will probably be able to see Halley’s Comets when it comes near the earth again.