In the universe, as we all know, there is the sun, the moon, the earth and a good many stars. Through our geography lessons, we know the earth goes around the sun, and the moon goes around 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.

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 farther, 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 out 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 actually the stars are much bigger and brighter than the moon. They look smaller than the moon also because they are farther away from the earth. There are many other planets in the universe. But of all the planets, only on the earth are there living things and people can only live on the earth, too. But at 9:00 a.m., October 15th, 2003, the Chinese pilot Yang Liwei was sent up in to space. He stayed there for 21 hours. It was the first time for Chinese to get into space.

Why is it called Mars? You might have asked yourself this before. Well, Mars is the name of the Roman god of war. People have seen the planet as a symbol of war for thousands of years. The ancient Greeks called the planet Ares after their god of war. Chinese people called it the“fire star" for the same reason.

Scientists have been interested in the planet since long before any space tasks. Egyptian scientists first saw Mars in the sky more than 4,000 years ago. Since then, people from all over the world have studied the planet.

Over the years, scientists have continued to study the planet and learned some basic things about it.

Mars is 10 times lighter and about 6 times smaller than Earth. Earth is 93 million miles (about 150 million km) from the sun, while Mars is 142 million miles away. That means it is much colder on Mars. In fact, the average temperature on Mars is - 62℃. Scientists found water on Mars long ago, but because of the low temperatures there, it is frozen. One day on Mars is called a sol and is about 40 minutes longer than one Earth day. The Red Planet's surface gravity is only 37% as strong as Earth's, meaning you would be able to jump nearly two times higher on Mars.

A． Earth               Mars

B． Earth             Mars

C． Earth               Mars

D． Earth               Mars

Astronauts go on spacewalks for many reasons. Spacewalks let astronauts work outside their spaceship while still in space. Astronauts can do science experiments on a spacewalk. Experiments can be placed on the outside of a spaceship. This lets scientists learn how being in space influences different things. Spacewalks also let astronauts repair satellites or spaceship that are in space. By going on spacewalks, astronauts can fix things instead of bringing them back to Earth to fix.

When astronauts go on spacewalks, they wear spacesuits to keep themselves safe. Inside spacesuits, astronauts have the oxygen（氧气）they need to breathe. They have the water they need to drink.

Astronauts put on their spacesuits several hours before a spacewalk. They leave the spaceship through a special door called an airlock. The airlock has two doors. When astronauts get ready to go on a spacewalk, they go through the first door and lock it tight behind them. They can then open the second door without any air getting out of the spaceship. After the spacewalk, astronauts go back inside through the airlock.

When on a spacewalk, astronauts use safety tethers to stay close to their spaceship. One end is tied to the spacewalker. The other end is connected to the spaceship. The safety tethers keep astronauts from flying away into space.