The Moon
The Moon is the only permanent natural satellite of the Earth. At about one-quarter the diameter of Earth, it is the largest natural satellite in the Sol System relative to the size of its planet. Orbiting Earth at an average distance of 238,900 miles, its gravitational influence slightly lengthens Earth's day and is the main driver of Earth's tides.
The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period, the amount of visible surface illuminated by the Sun varies from none up to 100%, resulting in lunar phases. The Moon is tidally locked to Earth, which means that a full rotation of the Moon on its own axis causes its same side to always face Earth. 59% of the total lunar surface can be seen from Earth through shifts in perspective due to libration.
The most widely accepted origin explanation posits that the Moon formed about 4.51 billion years ago, out of the debris from a giant impact between the planet and a hypothesized body called Theia. The near side of the Moon is marked by dark volcanic maria ("seas"), which fill the spaces between ancient crustal highlands and impact craters. The Moon's apparent size is nearly the same as that of the Sun, allowing it to cover the Sun almost completely during a total solar eclipse.
The first human-made artificial object to reach the Moon from the Earth was the Soviet Union's Luna 2 in 1959. The only human lunar missions to date have been those of the United States' Apollo program, which landed twelve men on the surface between 1969 and 1972.
Until 2016 it was inhabited, as it was the location of the Kingdom of Attilan.
Alternative Name(s)
Luna
Type
Planetoid / Moon
Location under
Included Locations
Included Organizations