The Moon has fascinated mankind throughout history. Telescopic observations revealed its surface has many overlapping craters. It is less dense than Earth. Current knowledge of the Moon is greater than any other solar system object except Earth, lending to a better understanding of geologic processes. The Moon orbits Earth every 27 days. It has no atmosphere, so temperatures vary greatly between day and night. Some interesting facts about the Moon are that it formed from Earth, it always shows the same face to Earth, its gravity is only 17% of Earth's, and only 12 people have ever walked on its surface.