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 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 actually (事实上) 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.

    There are many other planets in the universe. But of all the planets, only on the earth there are living things and people can only live on the earth, too. But at 9:00 a.m. 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.

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    Many people think the camel stores water in its hump (驼峰), but it does not. Instead, the camel stores something else there—food. The camel's hump is really a hump of fat (脂肪). The camel is often called "a ship of the desert". When the camel is not travelling and is in a place where there is much food and water, it eats and drinks a lot. As it does so, its hump rises from the fat its body makes. Then, when the camel is travelling through the desert and when there is no food, it can live off the stored fat.

    A camel can go on for days or weeks with little food or water. However, when its hunger reaches the starvation (饿死)point, its hump shrinks (收缩) and may even slip off its back and hang down its side.

    Camels are not fussy (挑剔的) about what they eat. Thorny (多刺的) plants don't hurt their mouths, grass of any kind will do and so will hay, dry grain and cactuses (干草, 干粮, 仙人掌).

There are one­ hump camels and two­ hump camels. Camels with one hump are called Arabian camels. They come from North Africa. Camels with two humps are from Asia.

    The world's forests become smaller and smaller. People are still cutting down the trees. Why is this happening? There are two reasons—land and wood. People need land for animals and crops. And people want wood. Japan, Europe and North American need wood. There, it is used for buildings or it is made into furniture.

    But most places from the forests are not good for animals or crops. The soil (土壤) in the forests is very thin. When trees are cut down, the soil is washed away by the rain or the wind. Soon there is nothing but sand. Then more land will be needed and more trees will be cut down.

    Life in space is much different from life on earth. How do astronauts live in space?

    Eating    In the past, astronauts could only eat small pieces of dried food. But now they are able to eat more everyday food like fruit, vegetables and ice-cream.

    Sleeping    All the people on the ISS（国际空间站）have their own rooms. They should be tied（系）to their beds, or they'll fly away! That seems like a hard way to sleep, but astronauts say sleeping is really not too bad.

    Exercising    This is more important in space than on earth. Astronauts exercise on bikes and other machines（机器）for about two hours every day. That way, they can still be healthy when they get back home.

    Having fun    Astronauts can read books, play cards, listen to music or send emails to their friends and families when they aren't working. Sometimes they just sit and look out of the window. It's also much fun!

    Is there intelligent (有智力的) life on other planets? For years, scientists said "no" or "we don't know". But today this is changing. Seth Shostak and Alexandra Barnett are astronomers (天文学家). They believe intelligent life exists (存在) somewhere in the universe. They also think we will soon contact these beings (人；生物).

    Why do Shostak and Barnett think intelligent life exists on other planets? The first reason is time. Scientists believe the universe is about 12 billion years old. "This is long enough for other planets to have intelligent life," say Shostak and Barnett. The second reason is size—the universe is huge. "Tools like the Hubble Telescope (哈勃望远镜) have shown that there are at least 100 billion galaxies," says Shostak. "And our galaxy, the Milky Way, has at least 100 billion stars. Some planets going around these stars might be similar to Earth."

    In the past, it was hard to look for signs of intelligent life in the universe. But now, powerful telescopes (高倍望远镜) allow scientists to discover smaller planets. These planets might have intelligent life.

    Have beings from space already visited Earth? "Probably not," says Shostak. However, intelligent beings may contact us in other way, such as radio signals (信号). In fact, they may be trying to communicate with us now, but we don't have the right tools to receive their messages. However, this is changing. By 2025, we could make contact with other life forms in our universe and we might help each other.