The speed at which the moon is moving away from the earth. Scientists have determined that the moon is moving away from the earth at an increasing speed
We know the structure of the solar system, where in the center is our luminary the Sun - the source of energy and life on Earth. The Sun is huge, its mass is approximately equal to 333,000 Earth masses, and its radius is 109 Earth radii. All planets revolve around the Sun and almost every planet has its own satellites. Our Earth is the third planet from the Sun and has one natural satellite- The moon. This Earth-Moon pair was formed approximately 4.5 billion years ago.
There are three hypotheses about the origin and appearance of the Moon:
1 Hypothesis:
It was put forward by J. Darwin at the end of the century. According to this hypothesis, the Moon and the Earth initially constituted one common molten mass, the rotation speed increased as it cooled and contracted, as a result, this mass was broken into two parts. The small one is the Moon, the large one is the Earth. This hypothesis explains the low density of the Moon, formed from the outer layers of the original mass. But there is a serious objection from the point of view of the existing geochemical differences between the rocks Earth's shell and lunar rocks.
2 Hypothesis:
The capture hypothesis, developed by the German scientist K. Weizsäcker, the Swedish scientist H. Alfvén and the American scientist G. Urey, suggests that the Moon was originally small planet, which, when passing near the Earth as a result of the influence of the latter’s gravity, turned into a satellite of the Earth.
The probability of such an event is very low, and, in addition, in this case one would expect a greater difference between the earth and lunar rocks.
3 Hypothesis:
According to the third hypothesis, developed by Soviet scientists - O. Yu. Schmidt and his followers in the mid-20th century, the Moon and Earth were formed simultaneously by combining and compacting a large swarm of small particles. But the Moon as a whole has a lower density than the Earth, so the substance of the protoplanetary cloud should have divided with the concentration of heavy elements in the Earth. In this regard, the assumption arose that the Earth, surrounded by a powerful atmosphere enriched with relatively volatile silicates, began to form first; with subsequent cooling, the matter in this atmosphere condensed into a ring of planetesimals, from which the Moon was formed.
The last hypothesis at the current level of knowledge (70s of the 20th century) seems to be the most preferable.
Currently, the Moon is located at a distance of 3.844 * 108 m from us. Measurement results show that the Moon is moving away annually by an average of 4 cm, and this leads to a slowdown of the Moon around the Earth. Therefore, we can already assume that over time the Moon will become closer to the Sun and will be the first to fall into its hot embrace.
Astronomer from the USA, Lee Anna Wilson from the University of Iowa, studying the fate of the Moon, calculated that over time it will make one revolution around the Earth not in 27.32 days, as now, but in big time. The Moon's orbit will be disrupted, it will be attracted faster by the Sun, weaker by the Earth until it gets to the point where the forces of gravity and the attractive forces of the Sun will tear it apart. The moon will crack and fall to pieces, i.e. our satellite will end its existence in the form of a ring of debris rotating around the Earth. This ring will be similar to the ring of Saturn.
According to preliminary calculations by scientists, this ring will not live long and in the end it will “rain”, that is, it will fall onto our Earth - first small particles, and then larger ones.
If it really comes to this, then our Earth will follow the Sun, but others are also possible alternative options. The Earth, having lost its satellite - the Moon, will revolve around the Sun alone for years. And a lot depends on the luminary itself - the Sun, because it will also change all the time. All these options are hypothetical, and we assume that we can look at this fact from a different perspective.
Now the Moon is moving away from the Earth. But when the day and month become equal, it will begin to approach. Will the Moon fall to Earth or not?
What is the future for the Earth-Moon system? If we extrapolate modern data on the rate of removal of the Moon, we can draw the following conclusion. The length of the day and month will increase all the time. In this case, the day will grow faster than the month, and in the distant future they will become equal. As a result, the Moon will always be visible from only one side of the Earth.
A system in which the planet and the satellite always “look” at each other with the same side already exists in the Solar System. These are Pluto and Charon. This is the most stable state in a TWO-body system. But the Earth is much closer to the Sun. Tidal forces from the Sun also slow down the Earth's rotation: the amplitude of solar tides is only slightly less than half the lunar tides. Therefore, after the Earth and Moon rotate synchronously, the Sun will continue to slow down the Earth's rotation. The Earth will begin to rotate around its axis SLOWER than the Moon in orbit. And this means that the Moon will be BELOW the synchronous orbit. Consequently, it will begin to fall to Earth.
Will all this end in a grandiose catastrophe in the history of the Earth?
A good scenario for a horror film: The moon is getting closer and closer, and it is impossible to stop it. After all, if the satellite ends up below the synchronous orbit, then its irreversible fall begins. Or not?
The satellite located below the synchronous orbit will “fall” on the planet, and the one located above will “fly away” from it. True, there is a significant clarification here. This will only happen if the planet's rotation speed remains constant. This is true for small satellites. And for the big ones? At what mass of the satellite can it already be considered large?
The answer is simple: if the orbital angular momentum of the satellite is comparable in magnitude to own moment momentum of the planet. In this case, the removal or approach of the satellite will significantly change the speed of rotation of the planet.
A simple calculation shows that in the Earth-Moon system, most of the total angular momentum falls on the Moon, and not on the Earth. Indeed, the angular momentum of the Earth is equal to:
Here I= 0.33 – dimensionless moment of inertia of the Earth, M- its mass, R– equatorial radius, V – linear velocity at the equator.
The orbital momentum of the Moon is:
Here m– mass of the Moon, r is the average radius of its orbit, v is the orbital speed.
The mass of the Moon is 80 times smaller than Earth, its orbital radius is 60 times greater than the radius of the Earth, and its orbital speed (1 km/sec) is 2 times greater than the equatorial rotation speed of the Earth (500 m/sec). Consequently, the orbital momentum of the Moon is approximately four times greater than the rotational moment of the Earth. Therefore, under no circumstances will the Moon be able to fall to Earth, even if in the distant future it ends up in a synchronous orbit.
As an example, let's assume that the Moon is in its current orbit, and the Earth does not rotate on its axis at all. In this case kinetic energy will be transmitted from the Moon to the Earth. The Earth will gradually begin to rotate, and the Moon will approach it: fall to the Earth. But it won't fall.
How close will the Moon be to Earth?
Orbital angular momentum is proportional to the orbital radius and speed. Orbital speed is inversely proportional to the square root of the radius. Therefore, the orbital momentum is proportional to the square root of the radius. If the orbital radius decreases by two percent, the torque will decrease by one percent. And this percentage, due to conservation, will be transferred to the Earth. Considering that the modern period of the Earth's rotation of one day corresponds to 25 percent of the lunar orbital momentum, then one percent will correspond to a period of 25 days. This period will be shorter than the lunar month, which, due to Kepler's third law, will decrease by only three percent and will be approximately 28 days. That is, the Earth will rotate FASTER than the Moon. Consequently, the Moon will NOT be able to approach the Earth even by 2 percent, but will approach a little less.
The future of the Earth-Moon system general outline such.
At first, the Moon will continue to move away from the Earth, receiving angular momentum from it. But the Earth does not have much angular momentum left - 25% of the Moon’s orbital angular momentum. Therefore, the maximum that the Moon can get is to increase its angular momentum by 25%. The radius of its orbit will increase by 1.5 times (1.25 squared). And the lunar month will increase approximately 2 times (according to Kepler’s Third Law, you need to raise 1.5 to the power of 3/2) and will be 60 days. Accordingly, the earth's day will also increase to 60 days. This is the MAXIMUM distance that the Moon can move away from the Earth.
How long will it take the Moon to move this distance from the Earth (half the radius of its current orbit)?
The distance to the moon is 380 thousand km, the removal rate is 3.8 cm/year. It is easy to calculate that the Moon will travel half its radius in five billion years if it moves away at a constant speed. But the removal rate will gradually decrease. So we'll have to add a few more billion years.
What will we do next?
The Sun will continue to slow down the Earth's rotation (solar tides).
But as soon as the Earth's rotation slows down, the Moon will move a little closer and the rotation will speed up again. The Sun will slow it down again, and the Moon will again approach and speed it up, and so on. The Earth is, in a sense, lucky to have the Moon. During its youth, when our planet rotated very quickly, it transferred its momentum to the Moon and thus preserved it. Indeed, under the influence of lunar tides, the Earth's angular momentum is not lost, but is only redistributed in the Earth-Moon system. And under the influence of weaker solar tides it is lost. But these tides can only take away angular momentum from the Earth. But for a long time now the main part of the angular momentum of the Earth-Moon system has been concentrated in the orbital motion of the Moon. And the solar tides cannot do anything with it. The Earth gave the lion's share of its rotation to the Moon, and there this share remains safe and sound. And after many billions of years, the Moon will gradually return its rotation to the Earth.
Among all the moons solar system, the Earth's most unique satellite. Due to its close location to the Earth, as well as its size, the Moon gives our planet a stable and stable position in its eternal path in orbit. That is, it must be said that the Earth-Moon connection maintains its position in outer space in a more or less uniform rotation.
The formation of the Moon occurred approximately 4.5 billion years ago, according to latest information scientists, the Moon has become younger, losing several million years. I must say that the history of the formation of the Moon is amazing. And the Earth’s satellite itself is extremely important for the existence of life on the planet. However, the Earth is also important for finding the Moon in its orbit.
As has been described more than once, billions of years ago, a cosmic object of no less smaller size crashes into a huge protoplanetary substance. It was then, from the molten mass - and this was the Earth - that huge pieces of matter were pulled out from the mass of the planet. Thrown into space, solid rocks are retained by the Earth's gravity.
Trying to escape the captivity of the Earth's gravity, but not having the strength to do so, they begin to gather into one large object. And under the influence of rotational forces, they turn into a ball. So, our Blue Planet has acquired an important component for the education and preservation of life.
It's amazing how precisely in time the space object arrived. No less surprising is the fact that someone’s hand placed both space object exactly in the position and at those points where it was necessary for the flourishing of life on Earth.
Before the impact and formation of the Moon, our planet was not yet blue, and rotated 4 times faster than it does now. The Earth's axis stood at an inclination of 10 degrees, and the Earth's day at that time was very short - only 6 hours. And the angle of inclination affected the average temperature on Earth.
At this time, the Moon had not yet entered its current orbit, and was 12 thousand times closer to the Earth. Exposing the planet strong influence powerful gravity. Soon, oceans began to form, and tidal friction began to slow the Earth's rotation. Over the course of 3 billion years, the formation of continents continued, and the speed of rotation of the planet continued to decrease, reaching 18 hours a day. After another half a billion years, the earth's day reaches 222 hours, and by adding seconds per year, it reaches 24 hours.
Why is the Moon so necessary for the Earth?
In fact, the Moon plays a very important role in the life of our planet. Firstly, it is necessary to note the gravitational force of the satellite, acting in conjunction with the Moon-Earth, our planet is in a stable orbit. And also, thanks to the Moon, our Blue Planet received an inclination angle of 23 degrees.
This degree of inclination can be called optimal; nature, as if specially took care of the comfort of human life on Earth. Indeed, thanks to this angle, the planet maintains a rather narrow range of temperatures. The sun's rays emitted by our luminary spread evenly across to the globe, which creates good conditions for life on Earth. The stability of sunrises and sunsets is also associated with the Moon on Earth, supporting the changes of seasons that are familiar to us.
The Moon also has a strong influence on the Earth's water basins. The tides ebb and flow, all this passes under the watchful eye of our companion. The Moon also maintains a 4-meter rise in water level at the equator.
What will happen if the Moon moves away from the Earth? What does the Moon's distance threaten the Earth with?
It is impossible to say that the Moon is eternal above the Earth, and it may happen that the Earth’s satellite will occupy a more distant orbit relative to our planet. Or he will completely go on a free voyage through outer space. After all, as you know, the Moon, although by a small amount, is still moving away from the Earth.
Experts have been observing the Moon for almost half a century. The first American astronauts left a reflector on the satellite. This helped to accurately measure the distance between the Moon and the Earth. And on Earth, the satellite was monitored by modern technology.
And experts were able to answer the question of how far the Moon is moving away from the Earth. It turned out that this is about 4 centimeters per year - not such a small amount, considering that the distance is increasing every year. However, this is not a constant amount of removal. As we know, the distance between the satellite and our planet is not constant. Hence the amount of removal is inaccurate.
Periodically, as the Moon moves away, the Earth's axis changes its tilt angle by 2-3 degrees, in one direction or another from the axis. But even this small value of a couple of degrees responds to natural disasters on Earth. And if the chain connecting the Earth and the Moon is broken, then the two space objects, having lost their buoyant attractive force, will simply scatter in the vastness of space. Released as if from a sling.
About 100 thousand years ago, a slight change in the angle of the axis led to the fact that Sun rays began to fall differently. This led to environmental disaster, - where forests once raged, wastelands scorched by the Sun formed. And as scientists suggest, it could have been the reason for the migration of the ancient inhabitants of the planet from Africa to the North. And in Europe and North America this even led to the beginning ice age, lasting for millennia.
And if the Moon breaks the Moon-Earth chain, then a time of catastrophe will come on the planet. The truth is very fleeting. Huge masses of water, held by the Moon, will immediately break free and move deep into the planet with a powerful, unrestrained force. Sweeping away and destroying everything in its path, the first to experience this will be the residents of New York and Rio de Janeiro.
In addition, having lost lunar protection, the Earth may fall under the gravitational influence of another planet. And then there is no need to talk about stability on Earth. The planet will have a different inclination, and a changeable one at that. Which will lead to strong temperature changes. There will also be a redistribution of water basins; the level may increase by hundreds of meters.
However, the Earth also has an impact on the Moon, for example, the rotation of our satellite has slowed down to one revolution per month. The Earth also slows down its rotation, this is influenced by the enormous frictional forces of ocean waves on the bottom. In this case, the tidal wave shifts from the point directly facing the Moon.
Much in the life of our planet is connected with the Moon. A lot can be explained from a scientific point of view. However, to answer the curious question - who so accurately adjusted the celestial mechanism, and placed all the cosmic bodies strictly in their places, on this moment no one can.
The influence of the Moon on Earth is difficult to overestimate. In particular, it keeps the Earth at an inclination of 66 degrees from the orbital plane. Thanks to this, the climate on most of our planet is quite good.
It is impossible to predict which side the Earth will turn to the Sun if the Moon leaves to wander through space. Presumably, it will literally lie on its side. Glaciers will melt, deserts will freeze, and the ebb and flow of tides will be forgotten. To understand how this threatens all life on the planet, just watch any apocalyptic film.
Meanwhile, Russian ufologists have already taken the version with the removal of the Moon in pencil and put forward a theory in their own style.
Ufologists have long considered the Moon as the closest base of alien civilizations to us,” ufologist Yuri Senkin told Vecherka. - The fact that telescopes, lunar rovers and people who have visited the Moon several times did not find them there can be explained simply - we examined only one side of the satellite. Reverse side no one studied it.
It is difficult to say what caused the Moon to move away, but it is possible that this is the work of aliens - or whatever they have instead of hands. And even if this is so, it is unlikely that this was done in order to harm our civilization. Alien races may pursue completely different goals. The Moon, for example, is rich in resources, including those that are in terrible short supply on Earth.
The Vecherka journalists were not at all inspired by the prospect of losing the Earth’s satellite: firstly, it would be quite boring at night without it, and secondly, they want to live some more. Therefore, we immediately turned to the P. K. Sternberg State Astronomical Institute for clarification.
The head of the Department of the Moon and Planets, Doctor of Physical and Mathematical Sciences Vladislav Shevchenko laughed for a long time after listening to the question. He asked me to repeat it. And he laughed again without stopping.
Oh storytellers! - he said, catching his breath. - But seriously, the Moon is indeed moving away from the Earth, but we must understand that this has been happening for four billion years, ever since the Moon itself was formed.
According to Shevchenko, the removal of the Earth’s satellite is quite natural physical phenomenon- remember school curriculum in physics, called inertia. Imagine that you are riding on a carousel. Spinning faster and faster, you feel yourself starting to lean in the direction opposite to the axis of the carousel. And if you don't grab onto something, you could simply be thrown out. But the Moon has nothing to cling to. The speed with which it rotates around the Earth sets such inertia that the Earth’s gravitational field is powerless to hold this ball. And you need to understand that gravity affects our satellite less and less as it moves away.
According to calculations, the Moon is moving away from the Earth by about 3.8 centimeters per year, continues Vladislav Shevchenko. - Now the distance to it is 384 thousand kilometers. And when the Moon was just forming, it was about 60 thousand kilometers. Just a stone's throw away! It took about four billion years for this distance to increase sixfold.
And it will take several more million years for the Moon to move away, ceasing to completely cover the Sun during an eclipse. Therefore, it is too early to worry about this. Just know: when this happens, “Evening Moscow” will notify you personally first.
There are several versions of the origin of the Moon, but in recent decades scientists have been leaning toward the theory of a giant collision. This happened about 4.6 billion years ago: the hypothetical planet Theia collided with the Earth tangentially, tearing out a huge piece from our long-suffering planet. The Earth immediately boiled, almost turning inside out, and the part of it that Theia tore out was captured by the Earth’s gravitational field, so that billions of years later we could lift our heads and say: “The moon is awesome today!”
INTERESTING FACT
Residents of the southern hemisphere see the Moon the other way around: for them it grows on the left, and decreases to the right.
First artificial satellite The Sun became the Soviet station "Luna 1" in 1959. Due to an error in the calculations, it missed the Earth's satellite at the second cosmic speed.
The smartphone your neighbor boy is carrying is many times more powerful than the computer that controlled the landing of astronauts on the moon.
Since time immemorial, the Moon has been a constant satellite of our planet and the closest to it celestial body. Naturally, people always wanted to visit there. But how far is it to fly there and how far is it?
The distance from the Earth to the Moon is theoretically measured from the center of the Moon to the center of the Earth. Measure this distance using the usual methods used in ordinary life, impossible. Therefore, the distance to the earth's satellite was calculated using trigonometric formulas.
Similar to the Sun, the Moon experiences constant movement in the earth's sky near the ecliptic. However, this movement is significantly different from the movement of the Sun. So the planes of the orbits of the Sun and Moon differ by 5 degrees. It would seem that, as a result of this, the trajectory of the Moon in the earth’s sky should be similar in general terms to the ecliptic, differing from it only by a shift of 5 degrees:
In this, the movement of the Moon resembles the movement of the Sun - from west to east, in the opposite direction to the daily rotation of the Earth. But in addition, the Moon moves across the earth's sky much faster than the Sun. This is due to the fact that the Earth revolves around the Sun in approximately 365 days (Earth year), and the Moon revolves around the Earth in only 29 days (lunar month). This difference became the impetus for dividing the ecliptic into 12 zodiacal constellations (in one month the Sun moves along the ecliptic by 30 degrees). During the lunar month, a complete change in the phases of the Moon occurs:
In addition to the trajectory of the Moon, there is also the factor of a very elongated orbit. The eccentricity of the Moon's orbit is 0.05 (for comparison, for the Earth this parameter is 0.017). The difference from the circular orbit of the Moon causes the apparent diameter of the Moon to constantly change from 29 to 32 arcminutes.
In one day, the Moon shifts relative to the stars by 13 degrees, and in an hour by about 0.5 degrees. Modern astronomers often use lunar occultations to estimate the angular diameters of stars near the ecliptic.
What determines the movement of the Moon?
An important point in the theory of the movement of the Moon is the fact that the Moon’s orbit in outer space is not constant and stable. Due to the relatively small mass of the Moon, it is subject to constant disturbances from more massive objects in the Solar System (primarily the Sun and Moon). In addition, the orbit of the Moon is influenced by the oblateness of the Sun and the gravitational fields of other planets in the Solar System. As a result, the eccentricity of the Moon's orbit fluctuates between 0.04 and 0.07 with a period of 9 years. The consequence of these changes was a phenomenon called a supermoon. A supermoon is an astronomical phenomenon during which full moon several times larger in angular dimensions than usual. So, during the full moon on November 14, 2016, the Moon was at a record high close range since 1948. In 1948, the Moon was 50 km closer than in 2016.
In addition, fluctuations in the inclination of the lunar orbit to the ecliptic are observed: by approximately 18 arc minutes every 19 years.
What is equal to
Spacecraft will have to spend a lot of time flying to the earth's satellite. You cannot fly to the Moon in a straight line - the planet will move in orbit away from the destination point, and the path will have to be adjusted. At a second escape velocity of 11 km/s (40,000 km/h), the flight will theoretically take about 10 hours, but in reality it will take longer. This is because the ship at the start gradually increases its speed in the atmosphere, bringing it to a value of 11 km/s, in order to escape from the Earth’s gravitational field. Then the ship will have to slow down as it approaches the Moon. By the way, this speed is the maximum that modern spacecraft have managed to achieve.
The notorious American flight to the Moon in 1969, according to official data, took 76 hours. NASA's New Horizons spacecraft managed to reach the Moon the fastest - in 8 hours and 35 minutes. True, he did not land on the planetoid, but flew past - he had a different mission.
Light from the Earth will reach our satellite very quickly - in 1.255 seconds. But flights at light speeds are still in the realm of science fiction.
You can try to imagine the path to the Moon in familiar terms. On foot at a speed of 5 km/h, the journey to the Moon will take about nine years. If you drive a car at a speed of 100 km/h, it will take 160 days to get to the earth’s satellite. If airplanes flew to the moon, the flight to it would last about 20 days.
How in ancient Greece astronomers calculated the distance to the Moon
The Moon became the first celestial body to which it was possible to calculate the distance from the Earth. It is believed that astronomers in Ancient Greece were the first to do this.
People have been trying to measure the distance to the Moon since time immemorial - Aristarchus of Samos was the first to try. He estimated the angle between the Moon and the Sun to be 87 degrees, so it turned out that the Moon closer to the sun 20 times (the cosine of an angle equal to 87 degrees is 1/20). The angle measurement error resulted in a 20-fold error; today it is known that this ratio is actually 1 to 400 (the angle is approximately 89.8 degrees). Big mistake was caused by the difficulty of estimating the exact angular distance between the Sun and Moon using primitive astronomical instruments Ancient world. Regular solar eclipses By this time, ancient Greek astronomers had already allowed them to conclude that the angular diameters of the Moon and the Sun were approximately the same. In this regard, Aristarchus concluded that the Moon smaller than the sun 20 times (actually about 400 times).
To calculate the sizes of the Sun and Moon relative to the Earth, Aristarchus used a different method. It's about about observations of lunar eclipses. By this time, ancient astronomers had already guessed the reasons for these phenomena: the Moon was eclipsed by the Earth's shadow.
The diagram above clearly shows that the difference in distances from the Earth to the Sun and to the Moon is proportional to the difference between the radii of the Earth and the Sun and the radii of the Earth and its shadow to the distance of the Moon. At the time of Aristarchus, it was already possible to estimate that the radius of the Moon is approximately 15 arc minutes, and the radius of the earth's shadow is 40 arc minutes. That is, the size of the Moon was approximately 3 times smaller than the size of the Earth. From here, knowing the angular radius of the Moon, one could easily estimate that the Moon is located about 40 Earth diameters from the Earth. The ancient Greeks could only approximately estimate the size of the Earth. Thus, Eratosthenes of Cyrene (276 - 195 BC), based on differences in the maximum height of the Sun above the horizon in Aswan and Alexandria during the summer solstice, determined that the radius of the Earth is close to 6287 km ( modern meaning 6371 km). If we substitute this value into Aristarchus’ estimate of the distance to the Moon, it will correspond to approximately 502 thousand km (the modern value of the average distance from the Earth to the Moon is 384 thousand km).
A little later, a mathematician and astronomer of the 2nd century BC. e. Hipparchus of Nicaea calculated that the distance to the earth's satellite is 60 times greater than the radius of our planet. His calculations were based on observations of the movement of the Moon and its periodic eclipses.
Since at the moment of the eclipse the Sun and the Moon will have the same angular dimensions, using the rules of similarity of triangles one can find the ratio of the distances to the Sun and to the Moon. This difference is 400 times. Applying these rules again, only in relation to the diameters of the Moon and the Earth, Hipparchus calculated that the diameter of the Earth is 2.5 times greater than the diameter of the Moon. That is, R l = R z /2.5.
At an angle of 1′, you can observe an object whose dimensions are 3,483 times smaller than the distance to it - this information was known to everyone in the time of Hipparchus. That is, with the observed radius of the Moon being 15′, it will be 15 times closer to the observer. Those. the ratio of the distance to the Moon to its radius will be equal to 3483/15 = 232 or S l = 232R l.
Accordingly, the distance to the Moon is 232 * R з /2.5 = 60 radii of the Earth. This turns out to be 6,371*60=382,260 km. The most interesting thing is that measurements made using modern instruments, confirmed the correctness of the ancient scientist.
Nowadays, the distance to the Moon is measured using laser instruments that allow it to be measured with an accuracy of several centimeters. In this case, measurements take place in a very short time - no more than 2 seconds, during which the Moon moves away in orbit approximately 50 meters from the point where the laser pulse was sent.
The evolution of methods for measuring the distance to the Moon
Only with the invention of the telescope were astronomers able to obtain more or less accurate values for the parameters of the Moon’s orbit and the correspondence of its size to the size of the Earth.
A more accurate method of measuring the distance to the Moon appeared in connection with the development of radar. The first radar survey of the Moon was carried out in 1946 in the USA and Great Britain. Radar made it possible to measure the distance to the Moon with an accuracy of several kilometers.
Laser ranging has become an even more accurate method for measuring the distance to the Moon. To implement it, several corner reflectors were installed on the Moon in the 1960s. It is interesting to note that the first experiments on laser ranging were carried out even before the installation of corner reflectors on the surface of the Moon. In 1962-1963, several experiments were carried out at the Crimean Observatory of the USSR on laser ranging of individual lunar craters using telescopes with a diameter of 0.3 to 2.6 meters. These experiments were able to determine the distance to the lunar surface with an accuracy of several hundred meters. In 1969-1972, Apollo astronauts delivered three corner reflectors to the surface of our satellite. Among them, the most advanced was the reflector of the Apollo 15 mission, since it consisted of 300 prisms, while the other two (Apollo 11 and Apollo 14 missions) only consisted of one hundred prisms each.
In addition, in 1970 and 1973, the USSR delivered two more French corner reflectors to the lunar surface on board the Lunokhod-1 and Lunokhod-2 self-propelled vehicles, each of which consisted of 14 prisms. The use of the first of these reflectors has an extraordinary history. During the first 6 months of operation of the Lunokhod with the reflector, it was possible to conduct about 20 laser ranging sessions. However, then, due to the unfortunate position of the lunar rover, it was not possible to use the reflector until 2010. Only photographs of the new LRO apparatus helped to clarify the position of the lunar rover with the reflector, and thereby resume work sessions with it.
In the USSR, the largest number of laser ranging sessions were carried out at the 2.6-meter telescope of the Crimean Observatory. Between 1976 and 1983, 1,400 measurements were taken with this telescope with an error of 25 centimeters, then observations were stopped due to the curtailment of the Soviet lunar program.
In total, from 1970 to 2010, approximately 17 thousand high-precision laser ranging sessions were carried out in the world. Most of them were associated with the Apollo 15 corner reflector (as mentioned above, it is the most advanced - with a record number of prisms):
Of the 40 observatories capable of performing laser ranging on the Moon, only a few can perform high-precision measurements:
Most of the ultra-precise measurements were made on a 2-meter telescope at the Mac Donald Observatory in Texas:
At the same time, the most accurate measurements are performed by the APOLLO instrument, which was installed on the 3.5-meter telescope at Apache Point Observatory in 2006. The accuracy of its measurements reaches one millimeter:
Evolution of the Moon and Earth system
The main goal of increasingly accurate measurements of the distance to the Moon is to attempt to gain a deeper understanding of the evolution of the Moon's orbit in the distant past and in the distant future. To date, astronomers have come to the conclusion that in the past the Moon was several times closer to the Earth, and also had a significantly shorter rotation period (that is, it was not tidally locked). This fact confirms the impact version of the formation of the Moon from the ejected material of the Earth, which prevails in our time. In addition, the tidal influence of the Moon causes the Earth's rotation speed around its axis to gradually slow down. The rate of this process is an increase in the Earth's day every year by 23 microseconds. In one year, the Moon moves away from the Earth by an average of 38 millimeters. It is estimated that if the Earth-Moon system survives the transformation of the Sun into a red giant, then after 50 billion years the Earth's day will be equal to the lunar month. As a result, the Moon and Earth will always face only one side towards each other, as is currently observed in the Pluto-Charon system. By this time, the Moon will move away to approximately 600 thousand kilometers, and the lunar month will increase to 47 days. In addition, it is assumed that evaporation earth's oceans in 2.3 billion years will lead to an acceleration of the process of removal of the Moon (Earth tides significantly slow down the process).
In addition, calculations show that in the future the Moon will again begin to move closer to the Earth due to tidal interaction with each other. When approaching the Earth at 12 thousand km, the Moon will be torn apart by tidal forces, the debris of the Moon will form a ring similar to the known rings around the giant planets of the Solar System. Other known satellites of the Solar System will repeat this fate much earlier. So Phobos is given 20-40 million years, and Triton is about 2 billion years old.
Every year, the distance to the earth’s satellite increases by an average of 4 cm. The reasons are the movement of the planetoid in a spiral orbit and the gradually decreasing power of gravitational interaction between the Earth and the Moon.
Between the Earth and the Moon, it is theoretically possible to place all the planets of the solar system. If you add up the diameters of all the planets, including Pluto, you get a value of 382,100 km.