An English student went to a city in the south of America to study there. He walked around the city to look for a warm room to live in.
　　One evening， he was walking along the street with a map in his hand. He saw a small board（木板）in the window of a house， the word“Room”was on it.
　　“What a nice room this is！”he said. “The windows are in the south side. The sun will come into the room during the day. I？蒺ll take it.”
　　But he was wrong. The sun is always on the north in that city. Do you know why？
　　In the old days people thought the moon much bigger than any other stars. Now we know the moon is much smaller than any other stars. It looks bigger than any other stars because it is much nearer to us.
　　People once thought the moon had fire on it， and the fire made it bright. Now we know the moon has no fire on it. It is bright because it gets light from the sun.
　　People thought the sun was the biggest and brightest of all the stars.Now we know many other stars are bigger and brighter than the sun. It is because the sun is nearer to us than many other stars.
　　When the sun shines everything looks bright. Can you feel the heat when you stand in the sun？The sun gives the heat from very far away. It is hard to believe that the sun is about one hundred and fifty million kilometres away. The sun looks small because it is so far from us， but it？蒺s really very huge.
　　The earth circles the sun. It takes one year for the earth to go around the sun. And at the same time the earth itself is spinning （自转）around once every twenty？鄄four hours.
　　The sun gives us light. It keeps us warm. It makes things grow. Plants， animals and people need the sun. We can not live without the sun.