The next astronomical object to Earth is the Moon. It is the natural satellite created as a result of collision of Earth and the hypothetical planet Teja about 4.5 billion years ago.
Orbit of the Moon in the ancient time
After collision, Teja's fragments were thrown out into Earth orbit. Then under the influence of gravitation they formed a celestial body - the Moon. The orbit of the Moon was at that time much closer, than today and was at distance of 15-20 thousand km. In a firmament its visible size then was in 20 times more. Since collision, the distance of the Moon from Earth increased and for today it averages 380 thousand kilometers
In antiquity the people tried to calculate distance to visible celestial bodies. So the Ancient Greek scientist and the philosopher Aristarkh Samossky, defined distance to the Moon 18 times closer than the Sun. In fact, this distance is 400 times less.
More exact Gipparkh according to which, the distance to the moon equaled to 30 terrestrial diameters had results of calculations. Its calculations were based on calculations of a circle of Earth of Eratosthenes. To today's measures it made 40,000 km that determined diameter of Earth in 12800 km. It corresponds to the valid modern parameters.
Modern data on an orbit of the Moon
Today the science has rather exact methods of determination of distances to space objects. During stay of astronauts on the Moon, they installed on its surface the laser reflector by which scientists with high precision determine the sizes of an orbit and distance to Earth now. The form of an orbit of the Moon is a little extended in an oval. The closest point to Earth (perigee) is at distance of 363 thousand km, the most distant (apogee) — 405 thousand km. The orbit has also considerable eccentricity 0.055. Because of it its visible sizes in the sky are quite various. Also the plane of an orbit of the Moon on 5 ° is inclined to Earth orbit plane. On Long's orbit moves with a speed of 1 km/s and bends around Earth in 29 days. Its location in the sky is displaced every night to the right, looking from the northern hemisphere, and for observers of the southern hemisphere — to the left. For them the visible disk of the Moon looks in the turned look. The moon is closer than the Sun by 400 times and so less it in the diameter therefore on Earth solar eclipses in accuracy the stars coinciding with the sizes of disks and the satellite are observed. And because of an elliptic orbit of Long in a distant point it is less in the diameter and thanks to it ring-shaped eclipses are visible. The moon gradually continues to move away from Earth on 4 cm a century therefore in the distant future of such eclipses as now, people should not observe any more.