Why the moon is turned one side to the Earth

Another side of the moon

The moon is always turned to the Earth on one side - this is due to the fact that for about 4.5 billion years of the Earth-Moon system, our natural satellite has undergone the effect of tidal capture.

The reason for the division of the moon into visible and reverse sides

Such an effect in a system of several celestial bodies, when a more massive body acts on the lighter so through its tidal forces that the light body gradually slows down (or accelerates) the speed of its rotation around its own axis comparing its frequency with the frequency of rotation around a heavy body. A light body also affects a heavier one, but this effect has less in proportion to differences in mass. So let's say the Moon, by its gravitational influence, gradually slows down the rotation of the Earth around its axis, thereby lengthening the Earth's day by 1 second in about 3 thousand years, but at the same time it takes several billion years before the tidal capture of the Earth by the Moon, although the Moon was captured quite a long time ago.

Why the moon is turned one side to the Earth

If the Moon still manages to carry out a gravitational capture of the Earth (and for this it would be necessary that the Sun, which had turned into a red giant by that time, doesn’t bother us), then the Moon can only be observed from the eastern or western hemisphere of the Earth, depending on at what point does the rotation stop. During the gravitational impact of the Moon on the Earth, energy is released in the form of sea and ocean tides that cause the moon to gradually lose kinetic energy, which causes it to be 38 mm away from us. With gravitational capture of the Earth, tides will cease on it, and the Moon will practically cease to move away from us - since the only source of energy loss by the Moon will be gravitational waves, the radiation power of which from the Earth-Moon system is very small (about 0.2 μW).

History of the study of the far side of the moon

From time immemorial, people have been attracted by unexplored corners of the Earth

Although the Magellan expedition back in 1522 proved that there was no end to the Earth, and with the achievement of Mount Everest by Edmund Hillary and Tenzing Norgay on May 29, 1953, there were almost no blank spots on Earth, but almost the entire Solar system remained a mystery to us Sputnik-1 flight on October 4, 1957, when the space age began. Thus, the gaze of researchers from the Earth went to the solar system and the moon became its closest target, and the most attractive place on it was its reverse side, which is always hidden from the earth observer

Why the moon is turned one side to the EarthEngraving of 1888 Flammarion depicting a medieval pilgrim reaching the edge of the earth and looking beyond the vault of heaven

The first pictures of the far side of the moon were made by the Luna-3 station, which was launched on October 4, 1959 - exactly two years after the launch of Sputnik-1. It took the station 3 days to reach the moon, and then an even more difficult stage began - the moon-3 needed to photograph a surface whose exact reflectivity no one could reliably predict. Therefore, electronic cameras (just starting their development) fell away, only the film remained. In order to accurately obtain high-quality images, photographing took place with two lenses with a focal length of 200 and 500 mm and a shutter speed from 1/200 to 1/800 second in increments of 1/200. For 40 minutes of shooting, 29 pictures were taken, covering 70% of the entire surface of the back of the moon, after development they were transmitted to the Earth using a traveling beam camera

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In total, 17 photos were transmitted to Earth, 6 of which were subsequently made public. Also on November 6, 1960, the "Atlas of the far side of the Moon" was published, which included 500 individual parts of the lunar surface (the International Astronomical Union approved the names of the details of the surface of the far side of the Moon on August 22, 1961). Especially for this station, the Yenisei photo-television system was made, which took pictures and transmitted them to the Earth, as well as the Chaika system, which carried out orientation using the Solar and Lunar sensors, which made Luna-3 the first device in the world oriented along 3 axes

According to the shooting program for the far side of the moon, two more devices were launched, but both of them could not enter the Earth’s orbit. Only the probe-3 station, which was launched on July 18, 1965, was able to get pictures of the back of the moon of better quality. 25 images transmitted by this station had a resolution of 860 × 1100 pixels and were much better, which made it possible to compile a new atlas covering already 95% of the lunar surface and having 4000 details.

The unmanned part of the US lunar program at that moment was almost completely aimed at providing manned flights (whose landings were assigned to the visible part of the moon). So the US achievements in studying the far side of the moon in the first half of the 60s were not great. For example, getting into this area of ​​the Moon Ranger-4, which was supposed to take its pictures. But due to the failure of the radio equipment, the main achievement of this mission was only that for the first time in the world, an object created by man reached the surface of the far side of the moon. Only the fifth apparatus from the Lunar Orbiter program launched at the end of 1967 was able to make a full-fledged survey of this area - when the places of future Apollo landing were already shot and scientists were given carte blanche to shoot those areas of the Moon that are most of them interested in.

Why the moon is turned one side to the EarthTopographic map of the moon, visible (left) and back side (right). The lowlands are depicted in blue on the map, the hills are shown in red

The Tsiolkovsky Crater (on the far side of the Moon) was proposed by scientists as a possible landing site for Apollon-18, and after the cancellation of this mission - as a place for landing Apollon-17. And although this position was also defended by the only scientist who visited the moon (just during this last Apollo 17 flight), geologist Harrison Schmitt - this landing site was considered too dangerous and abandoned it in favor of the Taurus-Littrov valley (which perhaps brought scientists even a bigger surprise, revealing traces of volcanic activity

Another side of the moon

The reverse side of the moon has a denser concentration of craters than the visible side. Since the Earth covers only 0.1% of the sky on the visible side of the Moon, a version with Earth protection of the visible side is considered unlikely. At the moment, the main version of this situation is that the gravitational impact of the Earth in the past caused more active geological processes on the visible side of the moon than on the back. The lava flowing out in such processes covered the craters on the visible side of the Moon, while the craters on the reverse side remained almost untouched

Why the moon is turned one side to the EarthMap of the far side of the moon

Future research and use
At the moment, the reverse side of the Moon is of interest as a place for placing radio telescopes (since the Moon’s thickness will shield the spurious signal coming from the Earth) and as a place for helium-3 production (since the visible side is partially screened by the Earth from exposure to the solar wind ) At the moment, not a single person or automatic vehicle has reached the surface of the lunar side of the moon, but according to the plans of the Chinese space program, by the end of 2018, the Chang'e-4 automatic interplanetary station with the second Chinese lunar rover should land on the far side of the moon

However, the greatest interest in the moon at the moment is manifested in terms of studying it itself. So the Chinese Chang'e-5 station is supposed to deliver samples from Mount Rumker, which is of volcanic origin. Also in China and the USA, missions are being prepared for the delivery of samples from the south pole of the moon, where, according to the Chandrayan-1 probe, water deposits were discovered. The United States indicates the largest crater on the lunar surface, the South Pole-Aitken basin, located in the southern region of the back of the moon, as the landing site for its device. The mysteries of the origin of the moon and its resources continue to await humanity