The Moon has fascinated mankind throughout the ages. By simply viewing with the naked eye, one can discern two
major types of terrain: relatively bright highlands and darker plains. By the middle of the 17th century, Galileo
and other early astronomers made telescopic observations, noting an almost endless overlapping of craters. It has
also been known for more than a century that the Moon is less dense than the Earth. Although a certain amount of
information was ascertained about the Moon before the space age, this new era has revealed many secrets barely
imaginable before that time. Current knowledge of the Moon is greater than for any other solar system object except
Earth. This lends to a greater understanding of geologic processes and further appreciation of the complexity of
terrestrial planets.