Astronomy (天文学) is the oldest science known to man. Thousands of years ago man looked at the stars and wondered about heavens(天堂). But the six planets that he could see with his eyes alone limited man.

    The Greeks studied astronomy over 2,000 years ago. They could see the size, color, and brightness of a star. They could see its place in the sky. They watched the stars move as the seasons changed. But the Greeks had no tools to help themselves study the heavens.

    Each new tool added to the field of astronomy helped man reach out into space. Until there were telescopes(望远镜), man did not know much about the moon. He did not know that the planet called Saturn(土星) had rings around it. His sight was so limited that he could not see all the planets. In the early 1700s, people thought there were only six planets. Pluto (冥王星), the last of the nine planets to be discovered was seen until 1930.

    Before the spectroscopes (分光镜), man didn't know what kind of gas was in the sun or other stars, without radio telescopes(射电望远镜), we did not know that radio noise came from far in space.

    Today, astronomy is a growing science. We have learned more in the past fifty years than in the whole history of astronomy.

    For nearly a century before there was such a thing as a space program, a view of space was possible. People could see full views of the Moon, explore Mars(探测火星),and study the outer space beauty. All of this was made possible by a small group of artist-astronomers(天文艺术家) who worked to show people how other worlds in space might look.

    Lucien Rudaux, a French artist, was the first to use his artistic ability and his knowledge of astronomy in art. His paintings show a mixture of skilled observations, brilliant imagination and careful attention. As a result, many of his works have come surprisingly close to actual conditions on distant planets. His painting of Mars included moonlike craters(火山口) that were first photographed by the astronauts in 1965. His 1930 painting of a dust storm looks remarkably like a photograph of a storm taken by the astronauts in 1976.

    The artist-astronomers, including Rudaux, made people interested in outer space by painting what turned out to be exact portraits of the planets.

    Another thing an astronaut has to learn about is eating in space．Food is weightless, just as men are.

    Food for space has to be packed in special ways．Some of it goes into tubes that a man can squeeze into his mouth．Bite-sized cookies are packed in plastic.

    There is a good reason for covering each bite．The plastic keeps pieces of food from traveling in the spaceship．On the earth very small pieces of food would simply fall to the floor．But gravity doesn't pull them to the floor when they are out of the plastic in a spaceship．They move here and there and can get into a man's eyes or into the spaceship's instruments．If any of the instruments is blocked, the astronauts may have trouble getting safely home.

    As astronauts travel on longer space trips, they must take time to sleep．An astronaut can fit himself to his seat with a kind of seat belt. Or, if he wants to, he can sleep in a sleeping bag which is fixed in place under his seat．But be careful he must put his hands under the belt when he goes to sleep．This is because he is really afraid that he might touch one of controls that isn't supposed to be touched until later.

    No one knows exactly the earth began. According to a widely accepted theory, the earth began with a “Big Bang”,exploded loudly and produced water vapor and many gases， (make) the earth's atmosphere. As the earth cooled down, water appeared and stayed the surface. It was the presence of waterallowed the earth to dissolve harmful gases and acids into the oceans and seas, which made possible for life to develop. First, the appearance of small plants encouraged the development of early shellfish and all sorts of fish. Next, green plants began to grow on land. were followed by land animals. So reptiles appeared for the first time. Later, dinosaurs developed.they suddenly disappeared. After that, mammals came into being. Finally, humans appeared and spread all over the earth. However, they are putting too much carbon dioxide into the atmosphere, making the earth too hot(live) on. So whether life will continue on the earth will depend on this problem can be solved.