The Moon

Luna - the only natural satellite. The distance from Earth to the Moon equal 384.4 thousand km. The diameter of the Moon is 3474 km, a little more than a quarter of Earth's diameter. Accordingly, the size of the moon in terms of only 2% of the Earth. Because of the smaller mass force of gravity on the moon is 6 times less than on Earth. Period of the Moon around the Earth is 27.3 days. Due to the fact that the moon has a sufficiently large mass and is relatively close to Earth, we observe the gravitational interaction between them, in the form of tides. Tides are more noticeable on the coasts of the oceans, where they reach values of several meters, as they exist in closed basins, and even in the crust. As a result of the tides is a loss of energy in the Earth-Moon system due to friction arising between the oceans and the bottom, and between the crust and mantle. This energy loss leads to the fact that the interaction force between the Earth and the Moon is constantly decreasing, this explains that the distance between the Earth and Moon growing by about 4 cm every year.

Moon is the only celestial body on which landed people. The first artificial object to break the Earth's gravity and flying near the Moon was the Soviet Luna 1. The first satellite, the age of the lunar surface was Luna 2. The first satellite, took pictures of the back side of the moon was Luna 3. All three of these lunar program was successfully completed in 1959. The first successful soft landing on the Moon was the Soviet Luna 9. The American moon program "Apollo" began in the early 60s of last century with the announcement of President Kennedy that the U.S. will launch a man on the moon before the end of the 60s. As a result of this program, the U.S. managed to make six successful missions to the moon in the interval between 1969 and 1972. After completion of the Apollo program of research of our natural satellite actually stopped for a period of more than 30 years. Only at the beginning of this century, several countries, including Russia, the United States and China announced the beginning of their lunar program, results of which should be the return of man to the moon.