Moon
Moon is the only natural satellite of Earth, and is a natural satellite of the 5th largest in the Solar System. Moon does not have its own light source and light the Moon actually comes from the reflection of sunlight.

The average distance from the center of the Earth-Moon to the center is 384,403 km, about 30 times the diameter of Earth. The diameter of the Moon is 3474 km, [1] is slightly smaller than a quarter the diameter of Earth. This means that the volume of the Moon is only about 2 percent of the volume of the Earth and the pull of gravity at its surface about 17 percent than the gravitational pull of the Earth. Month circulating around the Earth once every 27.3 days (orbital period), and periodic variations in the Earth-Moon system and the Sun is responsible for the occurrence of the phases of the Moon that repeats 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 pulled by Earth's gravity does not fall into 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 force attraction between the Earth and Moon. This causes the Moon further away from Earth at about 3.8 cm / year.

Moon is in synchronous orbit with Earth, this led to only one side of the Moon's surface that can be observed from Earth. Synchronous orbit causes kala kala rotation equal to its revolution.

In the month there is no air or water. Many craters on the lunar surface proceeds caused by the blow of a comet or asteroid. The absence of air and water on the moon causes the absence of erosion craters on the moon caused many millions of years old and still intact. Among the largest 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.

Moon is the only thing that ever visited the sky and landed humans. The first artificial objects that pass near the Moon was the Soviet Union's spacecraft, Luna 1, the first artificial object that hit the Moon's surface was Luna 2, and the first photograph the moon's far side that was never seen from Earth, taken by Luna 3, all missions carried out in 1959. The first spacecraft to successfully perform the landing was Luna 9, and the successful orbiting the Moon was Luna 10, both conducted in 1966. [1] Apollo program of the United States is the only manned missions to date, who performed six manned landings between 1969 and 1972.