The moon is a satellite of our planet, from time immemorial attracting the eyes of scientists and simply curious people. In the ancient world, both astrologers and astronomers devoted impressive treatises to her. Poets did not lag behind them. Today, in this sense, little has changed: the orbit of the moon, the features of its surface and bowels are carefully studied by astronomers. The compilers of horoscopes also keep their eyes on her. The influence of the satellite on the Earth is 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 formed at about the same time. The age of both bodies is 4.5 billion years. There are several theories of satellite origin. Each of them explains the individual features of the moon, but leaves a few unresolved issues. Closest to the truth today is the theory of a giant collision.
According to the hypothesis, a planet similar in size to Mars collided with a young Earth. The blow fell on a tangent and caused the release into space of most of the substance of this cosmic body, as well as a certain amount of terrestrial “material”. From this substance a new object was formed. The radius of the orbit of the moon was originally sixty thousand kilometers.
The giant collision hypothesis explains well many of the structural and chemical features 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 iron deficiency in the satellite can only be explained by the fact that by the time of the collision, differentiation of the inner layers occurred on both bodies. There is no evidence to date that this has occurred. Nevertheless, despite such counterarguments, the hypothesis of a giant collision is considered the main one in the whole world.
Parameters
The moon, like most other satellites, has no atmosphere. Only traces of oxygen, helium, neon and argon were found. The surface temperature in illuminated and dark areas is therefore very different. On the sunny side, it can rise to +120 Âş, and on the dark side it can drop to -160 Âş.
The average distance between the Earth and the Moon is 384 thousand km. In shape, the satellite is an almost perfect ball. The difference between the equatorial and polar radius is small. They are 1738.14 and 1735.97 km, respectively.
A full moon revolution around the Earth takes a little more than 27 days. The movement of a satellite in the sky for an observer is characterized by a phase change. The time from one full moon to another is slightly more than the specified period and is approximately 29.5 days. The difference arises because the Earth and the satellite also move around the Sun. The moon, in order to be in its original position, has to overcome a little more than one circle.
Earth-Moon System
The moon is a satellite, slightly different from other similar objects. Its main feature in this sense is mass. It is estimated at 7.35 * 10 22 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 on outer space, then its relationship with the characteristics of the planet is not typical. As a rule, the mass ratio in satellite-planet systems is somewhat less. Only Pluto and Charon can boast a similar ratio. These two cosmic bodies some time ago began to characterize as a system of two planets. It seems that this designation is true in the case of the Earth and the Moon.
Moon orbiting
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 orbit of the moon is an ellipse in shape. At different periods, the satellite is located closer to the planet, then further from it. The distance between the Earth and the Moon in this case varies from 363 104 to 405 696 kilometers.
One more evidence is connected with the satellite trajectory in favor of the assumption that the Earth with the satellite must be considered as a system consisting of two planets. The Moon’s orbit 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 trajectory of the satellite is slightly more than 5º.
The orbit of the movement of the moon around the earth is influenced by many factors. In this regard, the determination of the exact satellite trajectory is not an easy task.
A bit of history
A theory explaining how the moon moves was laid back in 1747. The author of the first calculations, which brought scientists closer to understanding the features of the satellite’s orbit, was the French mathematician Clerot. 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 gravity strongly diverged from the apparent movement of the satellite. Clero solved this problem.
The study of the issue was carried out by such famous scientists as D'Alembert and Laplace, Euler, Hill, Puizo and others. The modern theory of the circulation of the moon actually began with the works of Brown (1923). Studies by the British mathematician and astronomer helped bridge the gap between calculations and observation.
Challenging task
The movement of the moon consists of two main processes: rotation around the axis and revolution around our planet. It would not be so difficult to deduce a theory explaining the satellite’s movement if its orbit were not exposed to 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 disturb the orbit and to predict the exact position of the moon in a particular period becomes a difficult task. In order to understand what’s the matter, let’s dwell on some parameters of the satellite’s orbit.
Ascending and descending node, apse line
As already mentioned, the moon’s orbit is inclined toward 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. The imaginary line that connects these two points is denoted as a line of nodes.
The satellite closest to our planet is at the point of perigee. The maximum distance separates the two cosmic bodies when the moon is at its peak. The line connecting these two points is called the apse line.
Perturbations of the orbit
As a result of the influence on the satellite’s movement of a large number of factors at once, it essentially represents the sum of several movements. Let us consider the most noticeable disturbances arising.
The first of these is the regression of the line of nodes. The 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 opposite direction (therefore called regression) to the satellite’s movement. In other words, the plane of the moon’s orbit rotates in space. She needs 18.6 years for one full turn.
The apse line is also moving. The movement of the line connecting the apocenter and pericenter is expressed in the rotation of the orbit plane in the same direction where the moon moves. This happens much faster than in the case of line nodes. A full turn takes 8.9 years.
In addition, the lunar orbit experiences vibrations 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'. As in the case with the line of nodes, the period of such fluctuations is 18.6 years.
Finally, the orbit of the moon changes shape. It stretches a little, then returns to its original configuration. In this case, the eccentricity of the orbit (the degree of deviation of its shape from the circle) varies from 0.04 to 0.07. Change and return to original position take 8.9 years.
Not so simple
In fact, there are not so many four factors that need to be taken into account during calculations. However, they do not exhaust all the perturbations of the satellite’s orbit. In fact, each parameter of the motion of the moon is constantly affected by a large number of factors. All this complicates the task of predicting the exact location of the satellite. And taking into account all these parameters is often the most important task. For example, the calculation of the trajectory of the moon and its accuracy affects the success of the mission of the spacecraft sent to it.
The influence of the moon on the earth
The satellite of our planet is relatively small, but its effect is clearly visible. Perhaps everyone knows that it is the Moon that forms the tides on Earth. Here it is immediately necessary to make a reservation: the Sun also causes a similar effect, but due to the much greater distance, the tidal influence of the sun is not very noticeable. In addition, a 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 effect of the Sun on our planet is approximately two hundred times greater than the similar parameter of the Moon. However, tidal forces primarily depend on field heterogeneity. The distance separating the Earth and the Sun smooths them, so the effect of the moon close to us is more powerful (twice as much as in the case of the star).
A tidal wave forms on the side of the planet that is currently facing the night luminary. On the opposite side, a rush also occurs. If the Earth were motionless, then the wave would move from west to east, located exactly under the moon. Its full revolution would be completed in 27 or so days, that is, in the sidereal month. However, the period of rotation of the Earth around the axis is slightly less than 24 hours. As a result, the wave runs on the planet’s surface from east to west and completes one revolution in 24 hours and 48 minutes. Since the wave constantly meets the continents, it shifts forward in the direction of the Earth's motion and is ahead of the planet’s satellite in its run.
Moon orbit removal
A tidal wave causes the movement of a huge mass of water. This directly affects the movement of the satellite. An impressive part of the mass of the planet is shifted from the line connecting the centers of mass of two bodies, and attracts the moon to itself. As a result, the satellite is affected by a moment of force that accelerates its movement.
At the same time, continents running onto a tidal wave (they move faster than the wave, because the Earth rotates at a faster speed than the Moon rotates), are affected by the 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 passes into a higher orbit. This decreases the speed of the moon. In orbit, it begins to move more slowly. Something similar is happening with the Earth. It slows down, resulting in a gradual increase in the length of the day.
The moon is approximately 38 mm away from Earth. The studies of paleontologists and geologists confirm the calculations of astronomers. The process of a gradual deceleration of the Earth and the removal of the moon began about 4.5 billion years ago, that is, from the moment of the formation of two bodies. The researchers' data support the assumption that the lunar month was shorter and the Earth rotated at a faster speed.
A tidal wave arises 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 since these layers are not so malleable.
Removing the moon and slowing 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 “hangs” over one part of the surface. Earth and satellite will always be rotated by the same side to each other. It is appropriate to recall that part of this process has already been completed. It was tidal interaction that 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 in such equilibrium. These are already called Pluto and Charon.
The moon and the earth are in constant interaction. It cannot be said which of the bodies influences the other more. In this case, both are exposed to the sun. A significant role is played by other, more distant, cosmic bodies. Taking into account all such factors makes it rather difficult to accurately build and describe a model of the satellite’s motion in orbit around our planet. However, a huge amount of accumulated knowledge, as well as constantly improving equipment, make it possible to more or less accurately predict the position of the satellite at any time and predict the future that awaits each object individually and the Earth-Moon system as a whole.