The Moon
The rocks (岩石) on the moon tell us the moon is about 4.6 billion (十亿) years old, or about the same age as the Earth (地球). The moon is about one-fourth (四分之一) the size of the Earth. If the Earth is an apple, the moon is a hawthorn (山楂). The moon is very hot in the day and cold at night. This is because the moon has little air (空气) around it. The Earth has a lot of air around it. This keeps the Earth not too hot in the day and not too cold at night. There is no wind or water on the moon.