In the universe, as we know, 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 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 look smaller when they are farther, and small things also look bigger when they are nearer.

The sun is bright 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 still many other planets in the solar system (太阳系). All of them move round the sun. But of all these planets, only on the earth there are living things and people can only live on the earth too. At 9:00 am on October 15th, 2003, Chinese pilot Yang Liwei was sent up to space. He stayed there for 21 hours. It was the first time for Chinese to get into space.

Why is it called Mars（火星）? Well, Mars is the name of the Roman god of war（罗马战神）. People see the planet（星球）as a symbol of war for thousands of years. It is also known as the Red Planet because of its color. It is red because it’s rich in iron（铁）. Chinese people called it the “fire star” for the same reason.

Scientists was interested in the planet. They first saw Mars in the sky more than 4, 000 years ago. Then, people from all over the world studied the planet. About 200 years ago, scientists started to study pieces of Mars. They broke away and drifted（漂流）through space for millions of years before they got to Earth.

Scientists have learned some things about Mars. For example, Mars is home to a 21-kilometer-tall mountain—the tallest in our solar system（太阳系）. However, Qomolangma, Earth’s highest mountain, is just 9 kilometers tall. Like Earth, Mars has moons. It has two moons named Phobos and Deimos. The Red Planet also has the largest dust storms（沙尘暴）in the solar system. And they can last for months.

Earth is 10 times heavier than Mars. So The Red Planet’s gravity（重力）is only 37 percent as strong as Earth’s, meaning you can jump nearly two times higher on Mars. For the same reason, you are two times heavier on Earth than on Mars.