The moon accompanies our planet in its largespace travel for several billion years. And it shows us, to earthlings, from century to century, always the same moon landscape of its own. Why do we admire only one side of our companion? Does the moon rotate around its axis or does it float in motionless space?
Characteristics of our cosmic neighbor
В Солнечной системе имеются спутники гораздо larger than the moon. Ganymede - the satellite of Jupiter, for example, is twice as heavy as the Moon. But then it is the largest satellite relative to the mother planet. Its mass is more than a percent of the earth, and its diameter is about a quarter of the earth. Such proportions in the solar family of planets no longer exist.
Давайте попытаемся ответить на вопрос о том, does the moon rotate around its axis, after looking more closely at our closest cosmic neighbor. According to the theory adopted today in scientific circles, our planet acquired a natural satellite while still a protoplanet — not completely cooled, covered with an ocean of hot red-hot lava, as a result of a collision with another smaller planet. Therefore, the chemical compositions of the lunar and terrestrial soils are slightly different - the heavy cores of the colliding planets merged, which is why the earth’s rocks are richer in iron. The moon got the remains of the upper layers of both protoplanets, there is more stone there.
Does the moon rotate
To be precise, the question of whetherThe moon is not entirely correct. After all, like any satellite in our system, it wraps around the mother planet and spins around it around the star. But the axial rotation of the moon is not very usual.
No matter how much you look at the moon, she is always turned tous a crater of quiet and sea of tranquility. “And does the moon rotate around its axis?” - from century to century, humans have asked themselves the question. Strictly speaking, if you operate with geometric concepts, the answer depends on the chosen coordinate system. With respect to the Earth, the axial rotation of the Moon is indeed absent.
But from the point of view of the observer, locatedon the Sun-Earth line, the axial rotation of the moon will be clearly visible, with one polar rotation to a fraction of a second being equal in duration to the orbital one.
Интересно, что явление это в Солнечной системе не is unique. So, the satellite of the dwarf planet of Pluto Charon always looks at its planet with one side, the moons of Mars - Deimos and Phobos behave in the same way.
In scientific language, this is called synchronous rotation or tidal capture.
What is tide?
In order to understand the essence of this phenomenon and confidently answer the question of whether the moon rotates around its own axis, it is necessary to disassemble the essence of tidal phenomena.
Imagine two mountains on the surface of the moon,one of which "looks" directly at the Earth, the other is at the opposite point of the moon. Obviously, if both mountains were not part of the same celestial body, but revolved around our planet on their own, their rotation could not be synchronous, the one that is closer, according to the laws of Newtonian mechanics, should rotate faster. That is why the masses of the moon orb, located at points opposite to the Earth, tend to "run away from each other."
How the moon "stopped"
How do tidal forces on this or thatheavenly body, it is convenient to disassemble the example of our own planet. We, too, revolve around the moon, or rather the moon and the earth, as it should be in astrophysics, "lead a round dance" around the physical center of mass.
As a result of the action of tidal forces andthe closest and most distant point from the satellite the level of the water covering the Earth rises. Moreover, the maximum amplitude of the ebb and flow can reach 15 meters or more.
Another feature of this phenomenon isthe fact that these tidal “humps” daily bend around the surface of the planet against its rotation, creating friction at points 1 and 2, and thus slowly stop the globe in its rotation.
The impact of the Earth on the moon is much stronger due to the difference in mass. And although there is no ocean on the moon, tidal forces act no worse on stony rocks. And the result of their work is obvious.
So does the moon rotate around its axis? The answer is yes. But the rotation is closely connected with the movement around the planet. Over millions of years, tidal forces have leveled the axial rotation of the moon with the orbital one.
And what about the Earth?
Astrophysicists claim that right after the bigcollision, which caused the formation of the moon, the angular velocity of rotation of our planet was much more than now. Day lasted no more than five hours. But as a result of the friction of tidal waves about the ocean floor year after year, millennium after millennium, the rotation slowed down, and this day has been 24 hours.
В среднем каждый век прибавляет нашим суткам по 20-40 seconds. Scientists assume that in a couple of billion years our planet will look at the moon just like the moon at it, that is, on one side. The truth of this, most likely, will not happen, because even before the Sun, having turned into a red giant, “swallow” both the Earth and its faithful satellite - the Moon.
By the way, tidal forces give earthlings not onlyincrease and decrease in the level of the world ocean in the equatorial region. By acting on the mass of metals in the Earth’s core, deforming the hot center of our planet, the Moon helps to maintain it in a liquid state. And thanks to the active liquid core, our planet has its own magnetic field, protecting the entire biosphere from the murderous solar wind and deadly cosmic rays.
