The Moon is Earth's constant companion. It orbits our planet like a huge satellite. The Moon completes one orbit around the Earth in 27.3 days, while rotating on its own axis at the same time.
It moves around the Earth at a speed of 3700 kilometers per hour. The time between two identical phases_of_the_Moon is 29.5 days. Current research indicates that the Moon is 4.5 billion years old.
Although measurements have been made and rock samples taken, scientists do not agree on how the Moon was first formed. Different theories exist. One states that the Moon separated from the Earth because of its fast rotation (theory of formation by fission), another that the Moon was originally an independent planet, which was caught in the gravitational field of the Earth (theory of formation far from Earth). Another theory sees a simultaneous formation of the Moon and the Earth as the answer (double planet theory).
The following theory has been the most commonly accepted one since 1975: over four billion years ago, the Earth was struck by a large meteorite or other solid body (planetesimal), probably the size of Mars. The impact broke pieces off the Earth. These were caught in the same orbit and merged to form the Moon. However, the question of the Moon's origin has not been finally settled.
With its diameter of 3476 kilometers, the Moon is about a quarter the size of the Earth. Its mean distance to the Earth is approximately 384,404 kilometers. This distance fluctuates marginally, as the Moon has a slightly eccentric orbit. Therefore, the Moon does not travel at a constant speed in its orbit. When the Moon is closer to the Earth it is faster, becoming slower with increasing distance. For this reason the Moon's rotation lags a little behind its orbit, allowing us to sometimes see a small part of the usually hidden side.
Temperatures on the Moon range from 100┬░ Celsius on the side exposed to the Sun to minus 170┬░ Celsius on the dark side.
Little is known about the interior of the Moon. Scientists agree, however, that there is a solid crust made of granite-like rock and that the mantle, which lies below this crust also consists of rock. Further towards the interior of our satellite, there is a partially molten layer, where moonquakes occur. The Moon's core is probably made of metal. It probably consists of a mass of iron several hundred kilometers thick, which would explain certain magnetic phenomena on the Moon. All these issues have not yet been conclusively clarified.
