The moon is Earth's natural satellite that orbits our planet. It formed approximately 4.5 billion years ago from debris after a giant impact with Earth. While only one-fourth the size of Earth, the moon is the fifth largest moon in the solar system and has significant effects on our planet through its gravitational pull and influence on ocean tides. Some of the most notable events in our exploration of the moon include the first unmanned and manned landings by the Soviet and American space programs in the 1950s and 1960s.