The moon is Earth's only natural satellite. It is about one-quarter the size of Earth and orbits our planet at an average distance of about 239,000 miles (384,000 kilometers). The moon has no atmosphere, which means it has extreme temperatures, ranging from very hot during the day to very cold at night. The moon's surface is covered with craters, mountains, and lava flows, and it is thought to have formed about 4.5 billion years ago, not long after the formation of the Earth. The moon is in a sy