If you look at the moon,you may have many questions to ask.How big is the moon?How far is it from the earth?Is it like a ball or like a plate?Is it very hot or very cold out there?Are there living things on it?

 

　　After the telescope was invented in the seventeenth century,people got to know more and more about the moon.The moon rotates rather slowly and so one day on the moon is as long as two weeks on the earth,and one night is just as long.In the day time it is very　 hot on the moon,but it is very cold at night.This is because there is no air or water on it either to keep off the heat of the sun or to hold it.A man would not be able to live on the moon without a special suit.He would either freeze to death or be roasted dry.On the moon things are not as heavy as they are on the earth.Something that weighs a kiloramme on the earth would weigh only 166 gramms on the moon.

 

　　In 1969,the United States succeeded in sending a rocket to the moon and landing two astronauts on its surface.The astronauts have brought back to earth some moon rocks.Scientists have studied the rocks very carefully.They have found many elements in the moon rocks which are found on earth,but they have not been able to find any sign of life.