The moon is a satellite of our planet, attracting the eyes of scientists and just curious people from time immemorial. In the ancient world, both astrologers and astronomers devoted impressive treatises to her. The poets did not lag behind them. Today, little has changed in this sense: the orbit of the Moon, the features of its surface and interior are carefully studied by astronomers. Compilers of horoscopes also do not take their eyes off her. The influence of the satellite on the Earth is being studied by both. Astronomers study how the interaction of two cosmic bodies affects the movement and other processes of each. During the study of the moon, knowledge in this area has increased significantly.
Origin
According to scientists, the Earth and the Moon were formed at about the same time. Both bodies are 4.5 billion years old. There are several theories about the origin of the satellite. Each of them explains certain features of the Moon, but leaves several unresolved questions. The giant collision theory is considered the closest to the truth today.
According to the hypothesis, a planet similar in size to Mars collided with the young Earth. The impact was tangential and caused the release into space of most of the matter of this cosmic body, as well as a certain amount of terrestrial "material". From this substance, a new object was formed. The Moon's orbital radius was originally sixty thousand kilometers.
The hypothesis of a giant collision explains well many features of the structure and chemical composition of the satellite, most of the characteristics of the Moon-Earth system. However, if we take the theory as a basis, some facts still remain incomprehensible. Thus, the deficiency of iron on the satellite can only be explained by the fact that by the time of the collision, differentiation of the inner layers had occurred on both bodies. To date, there is no evidence that such a thing took place. And yet, despite such counterarguments, the hypothesis of a giant impact is considered to be the main one throughout the world.
Parameters
The moon, like most other satellites, has no atmosphere. Only traces of oxygen, helium, neon and argon have been found. The surface temperature in illuminated and dark areas is therefore very different. On the sunny side, it can rise to +120 ºС, and on the dark side it can drop to -160 ºС.
The average distance between the Earth and the Moon is 384,000 km. The shape of the satellite is almost a perfect sphere. The difference between the equatorial and polar radii is small. They are 1738.14 and 1735.97 km respectively.
Complete revolution of the Moon around the Earthtakes a little over 27 days. The movement of the satellite across the sky for the observer is characterized by a change of phases. The time from one full moon to another is somewhat longer than the indicated period and is approximately 29.5 days. The difference arises because the Earth and the satellite are also moving around the Sun. The moon has to travel a little more than one circle to return to its original position.
Earth-Moon System
The moon is a satellite, somewhat different from other similar objects. Its main feature in this sense is its mass. It is estimated at 7.351022 kg, which is approximately 1/81 of the same parameter of the Earth. And if the mass itself is not something out of the ordinary in space, then its relationship with the characteristics of the planet is atypical. As a rule, the mass ratio in satellite-planet systems is somewhat smaller. Only Pluto and Charon can boast of a similar ratio. These two cosmic bodies some time ago began to be characterized as a system of two planets. It seems that this designation is also valid in the case of the Earth and the Moon.
Moon in orbit
The satellite makes one revolution around the planet relative to the stars in a sidereal month, which lasts 27 days 7 hours and 42.2 minutes. The Moon's orbit is elliptical in shape. At different periods, the satellite is located either closer to the planet, or further away from it. The distance between the Earth and the Moon changes from 363,104 to 405,696 kilometers.
With satellite trajectoryone more proof is connected in favor of the assumption that the Earth with a satellite must be considered as a system consisting of two planets. The orbit of the Moon is not located near the equatorial plane of the Earth (as is typical for most satellites), but practically in the plane of rotation of the planet around the Sun. The angle between the ecliptic and the satellite's path is slightly more than 5º.
The orbit of the Moon around the Earth is influenced by many factors. In this regard, determining the exact trajectory of the satellite is not an easy task.
A bit of history
The theory explaining how the moon moves was laid back in 1747. The author of the first calculations that brought scientists closer to understanding the features of the satellite's orbit was the French mathematician Clairaut. Then, in the distant eighteenth century, the revolution of the Moon around the Earth was often put forward as an argument against Newton's theory. Calculations made using the law of universal gravitation differed greatly from the apparent movement of the satellite. Clairaut solved this problem.
The issue was studied by such well-known scientists as d'Alembert and Laplace, Euler, Hill, Puiseux and others. The modern theory of the revolution of the moon actually began with the work of Brown (1923). The research of the British mathematician and astronomer helped eliminate the discrepancies between calculations and observation.
Not an easy task
The movement of the Moon consists of two main processes: rotation around its axis and circulation around our planet. It would not be so difficult to derive a theory explaining the movement of the satellite ifits orbit was not affected by various factors. This is the attraction of the Sun, and the features of the shape of the Earth, and the gravitational fields of other planets. Such influences perturb the orbit and predict the exact position of the Moon in a particular period becomes a difficult task. In order to understand what is the matter here, let us dwell on some parameters of the satellite's orbit.
Ascending and descending node, line of apsides
As already mentioned, the Moon's orbit is inclined to the ecliptic. The trajectories of two bodies intersect at points called ascending and descending nodes. They are located on opposite sides of the orbit relative to the center of the system, that is, the Earth. An imaginary line that connects these two points is referred to as a line of knots.
The satellite is closest to our planet at the point of perigee. The maximum distance separates two space bodies when the Moon is at its apogee. The line connecting these two points is called the line of apsides.
Orbit disturbances
As a result of the influence of a large number of factors on the movement of the satellite, in fact, it is the sum of several movements. Consider the most noticeable of the emerging perturbations.
The first one is node line regression. The straight line connecting the two points of intersection of the plane of the lunar orbit and the ecliptic is not fixed in one place. It moves very slowly in the direction opposite (that's why it is called regression) to the movement of the satellite. In other words, the plane of the Moon's orbitrotates in space. It takes her 18.6 years to make one full rotation.
The line of apses is also moving. The movement of the straight line connecting the apocenter and periapsis is expressed in the rotation of the orbital plane in the same direction as the Moon moves. This happens much faster than in the case of a line of nodes. A full turn takes 8, 9 years.
In addition, the lunar orbit experiences fluctuations of a certain amplitude. Over time, the angle between its plane and the ecliptic changes. The range of values is from 4°59' to 5°17'. Just like in the case of the line of nodes, the period of such fluctuations is 18.6 years.
Finally, the Moon's orbit changes its shape. It stretches a little, then returns to its original configuration again. At the same time, the eccentricity of the orbit (the degree of deviation of its shape from a circle) changes from 0.04 to 0.07. Changes and return to its original position take 8.9 years.
It's not that simple
Actually, the four factors that need to be taken into account during the calculations are not so many. However, they do not exhaust all perturbations of the satellite's orbit. In fact, each parameter of the Moon's motion is constantly affected by a large number of factors. All this complicates the task of predicting the exact location of the satellite. And accounting for all these parameters is often the most important task. For example, the calculation of the Moon's trajectory and its accuracy affects the success of the mission of the spacecraft sent to it.
Influence of the Moon on the Earth
Our planet's satellite is relatively small, but its impact is goodnoticeably. Perhaps everyone knows that it is the Moon that forms the tides on Earth. Here we must immediately make a reservation: the Sun also causes a similar effect, but due to the much greater distance, the tidal effect of the star is little noticeable. In addition, the change in the water level in the seas and oceans is also associated with the peculiarities of the rotation of the Earth itself.
The gravitational influence of the Sun on our planet is about two hundred times greater than that of the Moon. However, tidal forces primarily depend on the inhomogeneity of the field. The distance separating the Earth and the Sun smooths them out, so the effect of the Moon close to us is more powerful (twice as significant as in the case of the luminary).
A tidal wave forms on the side of the planet that is currently facing the night star. On the opposite side, there is also a tide. If the Earth were stationary, then the wave would move from west to east, located exactly under the moon. Its full revolution would be completed in 27-odd days, that is, in a sidereal month. However, the period of rotation of the Earth around its axis is slightly less than 24 hours. As a result, the wave runs across the surface of the planet from east to west and completes one rotation in 24 hours and 48 minutes. Since the wave constantly meets with the continents, it shifts forward in the direction of the Earth's movement and outstrips the planet's satellite in its run.
Deleting the Moon's orbit
A tidal wave causes a huge mass of water to move. This directly affects the movement of the satellite. The imposing partThe mass of the planet is displaced from the line connecting the centers of mass of two bodies, and attracts the Moon to itself. As a result, the satellite experiences a moment of force, which accelerates its movement.
At the same time, the continents running on a tidal wave (they move faster than the wave, since the Earth rotates at a higher speed than the Moon does), experience a force that slows them down. This leads to a gradual slowdown in the rotation of our planet.
As a result of the tidal interaction of two bodies, as well as the action of the laws of conservation of energy and angular momentum, the satellite moves to a higher orbit. This reduces the speed of the moon. In orbit, it begins to move more slowly. Something similar happens with the Earth. It slows down, resulting in a gradual increase in the length of the day.
The moon is moving away from the Earth by about 38 mm per year. The studies of paleontologists and geologists confirm the calculations of astronomers. The process of gradual slowing down of the Earth and the removal of the Moon began approximately 4.5 billion years ago, that is, from the moment the two bodies formed. Researchers' data support the assumption that earlier the lunar month was shorter, and the Earth rotated at a faster speed.
The tidal wave occurs not only in the waters of the oceans. Similar processes occur both in the mantle and in the earth's crust. However, they are less noticeable because these layers are not as malleable.
The recession of the Moon and slowing down of the Earth will not happen forever. In the end, the period of rotation of the planet will be equal to the period of revolution of the satellite. The moon will "hover" over one areasurfaces. The earth and the satellite will always be turned by the same side to each other. Here it is appropriate to recall that part of this process has already been completed. It is tidal interaction that has led to the fact that the same side of the Moon is always visible in the sky. In space, there is an example of a system that is in such an equilibrium. These are already called Pluto and Charon.
Moon and Earth are in constant interaction. It is impossible to say which of the bodies has more influence on the other. At the same time, both are exposed to the sun. Other, more distant, cosmic bodies also play a significant role. Accounting for all such factors makes it quite difficult to accurately build and describe a model of a satellite's motion in orbit around our planet. However, a huge amount of accumulated knowledge, as well as constantly improving equipment, makes it possible to more or less accurately predict the position of a satellite at any time and predict the future that awaits each object individually and the Earth-Moon system as a whole.
