The moon is the only natural satellite of Earth, and is the largest natural satellite in the Solar System 5. The moon does not have its own light source and the light actually comes from the Moon reflected light of the Sun. The average distance from the Earth-Moon center to center is 384 403 km, about 30 times the diameter of Earth. Diameter of the Moon is 3474 km,  is slightly smaller than a quarter the diameter of Earth. This means that the volume of the Moon is only about 2 percent by volume of Earth and its gravitational pull on its surface about 17 percent rather than the Earth's gravitational pull. The moon revolves around Earth once every 27.3 days (orbital period), and periodic variations in the Earth-Moon system, the Sun is responsible for the occurrence of the phases of the Moon is repeated every 29.5 days (period sinodic). The density of the Moon (3.4 g / cm ³) is lighter than the density of the Earth (5.5 g / cm ³), while the mass of the Moon is only 0.012 Earth masses. Months drawn by the force of gravity does not fall to the Earth caused by the centrifugal force arising from the Moon's orbit around the Earth. The amount of centrifugal force the Moon is slightly larger than the gravitational attractive forces between the Earth and Moon. This causes the Moon farther away from Earth at about 3.8 cm / year. The moon is in synchronous orbit with the Earth, this led to only one side of the Moon's surface that can be observed from Earth. Synchronous orbit with the same rotation causes kala kala revolution. In the month there is no air or water. Terhasil many craters on the lunar surface is caused by a comet or asteroid hit. The absence of air and water on the moon cause the absence of erosion that causes a lot of craters on the moon millions of years old and still intact. Among the biggest is the Clavius ??crater with a diameter of 230 kilometers and as deep as 3.6 kilometers. A lack of air also causes no sound can be heard on the Moon. The moon is the only thing that ever visited the sky and landed humans. The first artificial object to pass near the Moon was the Soviet Union's spacecraft, Luna 1, the first artificial object to hit the lunar surface was Luna 2, and the first photograph the far side is never visible from Earth, taken by Luna 3, all of the mission carried out in of 1959. The first spacecraft to successfully perform the landing was Luna 9, and who successfully orbited the Moon was Luna 10, both made in 1966.  Apollo Program of the United States is the only manned missions to date, which made six manned landings between 1969 and 1972.
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