The moon is a natural satellite of the Earth. Mysterious and beautiful, it has attracted the eyes of astronomers since ancient times. Even then, many of its features were noticed: phase changes, the time of sunrise and sunset, the duration of the lunar month. Ancient scientists noticed the constancy of the image of the night luminary. True, in those days they did not wonder why the Moon was turned to the Earth on one side. For them, this was the only possible situation, which fully corresponded to the prevailing beliefs about the structure of the sky.
Today things are a little different. Our ideas about the motion and interaction of space objects, supported by numerous observations, are very different from those that existed in ancient times. And almost everyone from the school bench knows why the Moon is turned to the Earth on one side.
The beginning of the story
Today, one of the secrets that the Moon stubbornly does not want to reveal to us is its origin. Various studies conducted with the aim of obtaining a definitive answer to this question have so far generated several versions. According to one of them, the Moon and the Earth are sisters, formed at about the same time from a common protoplanetary cloud. The results of radioisotope analysis, which made it possible to determine the same age of two cosmic bodies, speak in favor of this. However, there is evidence of large differences in the composition of our planet and its satellite. A version is put forward to match it: the moon formed somewhere far in space and, approaching the Earth, was captured by it. Close to it is the hypothesis suggesting that several space objects were attracted, which, after some time, collided and formed the Moon. Finally, there is a theory according to which our planet is more likely a mother for its satellite: the Moon appeared as a result of the collision of the Earth with a huge body. The embossed part subsequently began to rotate in orbit around the "progenitor".
Satellite-planet system
Be that as it may, it is only known for certain that the Moon is a natural satellite of the Earth. According to astronomical data, the night luminary at the time of its formation was located much closer to our planet. Moreover, it flew faster around the Earth and turned one side or the other. This situation is characteristic of the initial stage of the evolution of the satellite-planet system. An example of the outcome of the development of such a “relationship” is Pluto and its accompanying Charon. Both cosmic bodies are always turned to each other by one side, their rotation is synchronized. But first things first.
Tidal acceleration
The young moon immediately began to affect the earth. This was expressed in the formation of tidal waves in the recently emerging oceans, as well as in the crust. This effect has two main consequences. Firstly, as a result of some structural features of the Earth and its rotation, the tidal wave is ahead of the Moon. The entire mass of our planet, enclosed in such waves, in turn, acts on the satellite, gives it acceleration, and the Moon begins to move faster, gradually moving away from the Earth. Secondly, in this process, an oppositely directed force also arises, inhibiting the movement of the continents. As a result, the speed of the Earth's rotation around its axis decreases, and the length of the day increases.
The moon moves about 4 cm per year from our planet. However, this is not an eternal process, and the probability of the Earth losing its satellite is negligible. The “escape” of the Moon will end at the moment when the Earth's rotation around the axis is synchronized with the satellite’s orbital motion. In this case, our planet will always look at the night luminary on the same side.
Similar process
It is easy to assume that the answer to the question of why the Moon is turned to the Earth on one side is associated with a similar phenomenon. Indeed, the Earth's gravitational force causes similar tidal waves in the bowels of the satellite. Since our planet is more massive, the strength of its impact is much more tangible. Obeying her, the Moon has long synchronized its rotation with the movement around the Earth. As a result, the always visible and invisible side of the moon appeared.
Just over half
An attentive amateur astronomer can quickly enough find that the face of the night luminary is still changing somewhat. The visible side of the moon does not occupy exactly half of it. The orbit of the night luminary deviates from the plane of the Earth's rotation around the Sun (ecliptic) by about 5º. In addition, its axis is offset by 1.5º relative to the trajectory of the moon. As a result, up to 6.5 ° above and below the satellite poles are available for observation. This process is called lunar latitude libration. Similarly, there is a fluctuation in the longitude of the satellite. It is caused by a change in the speed of the moon, depending on the distance to the Earth. The part of the satellite hidden from the eyes due to this is reduced, and the other side of the moon, illuminated, increases to 7º longitude. So it turns out that in total, you can observe up to 59% of the lunar surface.
In the distant future
So, the question of why the Moon always looks at the Earth on one side finds an answer in the peculiarities of the influence of the planet’s gravitational force on the satellite. However, as was said, a similar process after a certain time will lead to the fact that the Earth will look at the night luminary with only one part of it, regardless of what phase the moon is in. According to the calculations of John Darwin, the grandson of the founder of the theory of evolution, the length of the day by this moment will be fifty days familiar to us. The distance separating the Earth and the Moon will increase by about one and a half times. This will be the very ideal state of the satellite-planet system.
Sun tides
True, there is some likelihood that the moon is never destined to achieve sufficient removal. The reason for this possibility lies in the solar tides. The daylight has a similar lunar effect on both the planet and the satellite. If this fact is included in the theoretical construction of the future of two cosmic bodies, it turns out that at a certain distance from the Earth, the Moon will again approach. This reduction in distance will have devastating consequences. When the Moon is at a distance of 2.9 radii of the Earth, it will be torn apart by gravity.
Another “but”
However, this picture may not be realized. The fact is that, according to forecasts, the removal of the moon, then its approach and, finally, death will take several trillion years. During this time, a catastrophe of a more serious scale can happen, at least for all living things on the planet. The Sun, which has exhausted all stellar fuel reserves, will go out. Following this, all the conditions of interaction in the planetary system of the luminary will change.
Study
The other side of the moon, inaccessible to direct observation, for a long time was a mystery, literally covered in darkness. Only the beginning of the space age gave us the opportunity to get to know her better. The first aircraft to photograph about 70% of the surface of the hidden part was the Soviet Luna-3. The images transmitted to the Earth showed that the relief of the back side is somewhat different from the nature of the visible surface. There were practically no plains of the seas. Only two such formations were discovered, later named the Sea of Moscow and the Sea of Dreams.
Giant crater
In 1965, the Zond-3 spacecraft headed toward the moon. He completed the survey of the invisible part of the satellite. The image of the remaining 30% of the surface only confirmed the conclusions made earlier: the surface in this part is covered with craters and mountains, but there are practically no seas on it.
The most impressive size is one of the craters, located precisely on the dark side of the moon. Its length is 2250 km, and the depth is 12 km.
Hypotheses
Today, the secrets of the far side of the moon are largely unraveled. However, the human mind tends to fantasize about those things and phenomena that are inaccessible to direct observation. Therefore, on the Internet, it is easy to meet the most bizarre hypotheses related to the entire moon as a whole or only to its side hidden from the eyes. There are assumptions about the artificial origin of the satellite, its population by extraterrestrial intelligence and the intentional concealment of one of the parties. There are also references to the mysterious space base located on the dark part of the satellite. Such versions are quite difficult both to confirm and to refute. No matter how true or false they are, they are based on the same reason that prompted people to explore space: the hope to find fellow minds in the vast expanses of the Universe, the desire to touch the unknown.
However, today it is quite accurately known why the Moon is turned to the Earth on one side. And the assumption of artificial origin did not receive any serious continuation. The answer to this question became as obvious as understanding what phase the moon is in today and why. It is impossible, however, to say that we know everything about the earth satellite and no discoveries are expected in the future. On the contrary, the night luminary to match the ancient deities personifying it, remains mysterious and in no hurry to share secrets. Mankind has yet to learn a lot of interesting things about the satellite of our planet. Perhaps a new stage of study, which began recently, will bear fruit in the near future. It is absolutely certain that the implementation of some NASA projects is of great importance in this sense. Among them is Avatar, which consists in developing a telepresence costume. It will allow, being on Earth, with the help of robots to conduct experiments on the moon. Great hopes are also assigned to the colonization project, the implementation of which will result in the deployment of a scientific base on the satellite of our planet.