The natural satellite of Earth is the Moon. It is the fifth-largest moon in the Solar System and the largest relative to the size of its planet. The Moon plays a significant role in shaping Earth's tides due to its gravitational pull. Its surface is marked by craters, valleys, and maria – large, dark basaltic plains formed by ancient volcanic eruptions. The Moon has been the subject of human exploration, most notably during the Apollo program, with Apollo 11 being the first mission to land astronauts on its surface in 1969. Its phases and visibility have inspired countless cultures and mythologies throughout history.