Luna

The Moon (Latin : Luna) is Earth's only natural satellite, and is the fifth largest one in the Solar system . The average centre-to-centre distance from the Earth to the Moon is 384,403 km, which is about thirty times the diameter of the Earth. The Moon has a diameter of 3,474 km —slightly more than a quarter that of the Earth, and about two-thirds of the average east–west distance across the United States. This means that the volume of the Moon is about 2 percent that of Earth. The gravitional pull at its surface is about 17 percent of the Earth's. The Moon makes a complete orbit around the Earth every 27.3 days, and the periodic variations in the geometry of the Earth–Moon–Sun system are responsible for the lunar phases that repeat every 29.5 days.

The Moon is the only calestial body to which humans have travelled and upon which humans have landed. The first artificial object to escape Earth's gravity and pass near the Moon was the Soviets Union's Luna 1, the first artificial object to impact the lunar surface was Luna 2, and the first photographs of the normally occluded Far side of moon were made by Luna 3, all in 1959. The first spacecraft to perform a successful lunar soft landing was Luna 9, and the first unmanned vehicle to orbit the Moon was Luna 4, both in 1966. The United State (U.S.) Apollo program achieved the only manned missions to date, resulting in six landings between 1969 and 1972. Human exploration of the Moon ceased with the conclusion of the Apollo program, although several countries have announced plans to send people or robotic spacecraft to the Moon.