日期：2008-07-30 the earth we live on is a planet. Are there people living on any other planets？ answer this question， we have to talk out why there are people on the earth. A few billion years ago， the earth was only a sea of fire. There was no life on the earth... 阅读全文>>

日期：2008-07-30 The moon is the closest star to the earth. It is over 380，000 kilometres from us. It takes 100 days for us to get there by train or 16 days by airplane. The sun is much farther away. It is 150 million kilometres from us-400 times farther than the m... 阅读全文>>

日期：2008-07-30 There are many， kinds of stars. Some are big and some are small. There arc nine planets revolving around the sun. The earth is， one of them. Of the nine planets， Jupiter is the biggest. It is one thousand times larger than the earth. But Mercury... 阅读全文>>

日期：2008-07-30 In the clear sky in summer and autumn， we can see， besides other stars， a silvery belt that looks like a river. People call it the Milky Way. This is formed by thousands of stars. If we look at them through a telescope， we can see the Milky Way i... 阅读全文>>

日期：2008-07-30 There are more stars in some parts of the sky than in others. The place that has the most stars is known as the Milky Way， or the Galaxy. From different positions， the number of stars is different. In summer most of the stars we see are those loca... 阅读全文>>

日期：2008-07-30 Besides white stars， there are also yellow， red and blue ones. The colour of the star is decided by its temperature. When we put a piece of iron over a fire， it becomes red first； when it becomes hotter， the colour yellow； finally， when it is... 阅读全文>>

日期：2008-07-30 Sometimes there are more stars in the sky than others. This has a lot to do with the cloud in the sky. If the cloud is thick， it will cover the star light and we won't be able to see many stars. When there is no cloud， there is less steam in the ai... 阅读全文>>

日期：2008-07-30 When you turn the light off at night， the room becomes very dark. When you light a candle in the dark room， it seems very bright. But if you turn on the light and put the candle beside the lamp， the candle will look dim. This is the same with the... 阅读全文>>

日期：2008-07-30 At night sometimes the stars twinkle like people blinking their eyes. Actually， it is the air playing a trick. The earth we live on is surrounded by a thick layer of air. Some is dry cold air and some is wet， hot and steamy. These air currents are... 阅读全文>>

日期：2008-07-30 When the stars shine in the evening sky， they are like many lights in the sky. How do the stars shine？ As we have already learned the sun is bright and hot like a huge furnace. It is fuelled by atomic energy which causes it to shine and give out he... 阅读全文>>

日期：2008-07-30 The moon， like the earth， is round all the time. Why then does the moon we see everyday change its shape？ The moon does not shine by itself. It is the sun-light that illuminates the moon so that we can see it. As the moon keeps revolving around th... 阅读全文>>

日期：2008-07-30 Like the earth， there are mountains， valleys and flat land on the moon. However， on the moon there are no trees in the mountain， there is no water in the valleys and there is no grass on the flat land. Nor is there air or water on the moon. It is... 阅读全文>>

日期：2008-07-30 When you travel by train and look out the window， you'll feel the lamp posts and houses all run backwards. But when you look carefully， you'll find the objects closer to the train run faster than those farther away. Mountains and big trees seem to... 阅读全文>>

日期：2008-07-30 Let's do a simple test first. Take a big balloon and a small apple and put them together. Which is bigger？ The balloon， of course. Now， put the apple in front of your eyes and put the balloon as faraway as possible. Now look again. Why， the bal-... 阅读全文>>

日期：2008-07-30 The sun appears to be as big as the moon. A dually， the sun is 100 million times bigger than the moon. So why does the sun look just as big as the moon？ This is because the sun is farther away from the earth than the moon.... 阅读全文>>

日期：2008-07-30 During the day time we can see the sun， but we cannot see it after sunset. Why is that？ The earth revolves all the time. During the day the earth faces the sun. As the earth turns its back to the sun， it becomes night and we cannot see it. It is t... 阅读全文>>

日期：2008-07-30 Our hands are small. But if you put one hand over your eyes， you won't be able to see the sky. When we look at things， those near us always appear bigger than those farther away. The sun is big but it is very， very far from us. it is like a disc.... 阅读全文>>

日期：2008-07-30 The sun brings us light and warmth. But what can we do if the sun burns out？ There is no need to worry. The sun is like a big stove using atom energy as its fuel. It bums and bums， giving out tremendous light and heat. Do you know how old the sun... 阅读全文>>

日期：2008-07-30 Although the sun is over one million kilometres away from us， we still feel its heat. In this sense， we can say that the sun is a very big fire ball. The temperature on the surface of the sun is 6，000'C. The temperature is much higher deep inside... 阅读全文>>

日期：2008-07-30 In the sky there is a very thick layer of air which is colourless. So why does the sky look blue？ It has something to do with the irradiation of sunlight. Sunlight is formed by the seven colours of red， orange， yellow， green， blue， indigo-blue... 阅读全文>>