It is called the front. On the other hand, except for the area near the edge of the moon, which is visible in the middle due to Libra movement, most areas on the back of the moon are invisible from the earth. In the era without detectors, the back of the moon has always been an unknown world. A major feature of the back of the moon is that there are almost no dark lunar surface features such as the moon and the sea. When the artificial probe runs to the back of the moon, it will not be able to communicate directly with the earth. The moon orbits the earth in 27.32 1666 days, and moves half a degree relative to the background starry sky every hour, which is similar to the apparent diameter of the moon. Unlike other satellites, the orbital plane of the moon is closer to the ecliptic plane than the equatorial plane of the earth. Relative to the background starry sky, the time required for the moon to go around the earth (the moon makes one revolution) is called sidereal month; The time between the new moon and the next one (or the time between two identical moon phases) is called the new moon. The reason why Wang Shuo's moon is longer than that of the star moon is that during the earth's operation on the moon, it moved forward a certain distance in its orbit around the sun. Because the rotation period of the moon is exactly the same as that of its period of revolution, it can only be seen from the earth that the moon always faces the earth with the same face. From the early days of the formation of the moon, the earth was affected by a moment, which led to the slow rotation speed. This process is called tidal locking. Therefore, part of the angular momentum of the earth's rotation is converted into the angular momentum of the moon's revolution around the earth. As a result, the moon is far away from the earth at a speed of about 38 mm per year. At the same time, the earth's rotation is getting slower and slower, and the length of a day is getting longer every year 15 microsecond. The gravity exerted by the moon on the earth is one of the reasons for the tidal phenomenon. The orbit of the moon around the earth is synchronous, and the so-called synchronous rotation is not strict. Because the orbit of the moon is elliptical, when the moon is at perigee, its rotation speed can't keep up with the revolution speed, so we can see that the eastern part of the moon reaches 98 degrees east longitude. On the contrary, when it is at the apogee in the middle of the month, its rotation speed is faster than its revolution speed, so we can see that the western part of the moon passes through 98 degrees Darcy. This phenomenon is called meridian libration. Looking at the earth from the moon
Strictly speaking, both the earth and the moon revolve around the center of mass, which is 4,700 kilometers away from the center of the earth (that is, 3/4 of radius of the earth). Because the center of homogeneity is below the surface, the movement of the earth around the center of homogeneity seems to be "shaking". Seen from the south pole of the earth, both the earth and the moon rotate clockwise; Moreover, the moon also orbits the earth counterclockwise; Even the earth moves clockwise around the sun. This phenomenon occurs because the angular momentum of the earth and the moon relative to the sun is the same, that is, "they have been rotating in this direction from the beginning." Many people don't understand why the inclination of the moon's orbit and the inclination of the moon from the axis change so much. In fact, the orbital inclination is relative to the central celestial body (the earth), from the axial inclination to the satellite. The orbit plane of the moon (ecliptic plane) keeps an included angle of 5. 145396 with the ecliptic plane (earth's orbit plane), while the rotation axis of the moon forms an included angle of 1.5424 with the normal of the ecliptic plane. Because the earth is not a perfect sphere, but bulges at the equator, the white road surface keeps precessing (that is, the intersection with the ecliptic rotates clockwise) and completes one week every 6793.5 days (18.5966). During this period, the angle between the white plane and the equatorial plane of the earth (the equatorial plane of the earth inclines to the ecliptic plane at 23.45) will change from 28.60 (i.e. 23.45+5. 15) to18.30 (i.e. 23.45-5. 15). Similarly, the angle between the rotation axis of the moon and the white plane will be between 6.69 (that is, 5. 15+ 1.54) and 3.60 (that is, 5. 15- 1.54). These changes in the lunar orbit will in turn affect the inclination of the earth's rotation axis, making it swing by 0.002 56, which is called nutation. The two intersections between the ecliptic plane and the ecliptic plane are called the lunar intersection-the ascending intersection (north point) refers to the point where the moon passes to the north of the ecliptic plane; Descending node (South Point) refers to the point where the moon passes south of the ecliptic. When the new moon is just at the intersection of the moon, a solar eclipse will occur; An eclipse occurs when the full moon is just at the intersection of the moons. The structure on the back of the moon is quite different from that on the front. The Moon Sea occupies less land and there are many craters. The terrain is uneven, and the longest and shortest radius of the moon are located on the back. Some places are 4 kilometers longer than the average radius of the moon, and some places are 5 kilometers shorter (such as Van der Graf depression). No "lump" was found on the back. The moon shell on the back is thicker than that on the front, with the thickest point reaching 150km, while the thickness of the moon shell on the front is only about 60km. A map on the back of the moon
The moon itself does not shine, but reflects sunlight. The brightness of the moon varies with the angular distance between the sun and the moon and the distance between the earth and the moon. The average brightness is 1/465000 of the brightness of the sun, and the brightness varies from 1/630000 to 1/375000. At the full moon, the average brightness is-12.7 (see). Its average illumination to the earth is 0.22 lux, which is equivalent to the illumination of 100 watt electric lamp at a distance of 2 1 meter. The surface of the moon is not a good reflector. Its average albedo is only 7%, and the other 93% is absorbed by the moon. The albedo of Guangdong Sea is even lower, about 6%. The albedo of the lunar highlands and craters is 17%, and it seems that the mountains are brighter than the moon sea. The brightness of the moon changes accordingly, and the brightness of the full moon is more than ten times that of the upper and lower chords. Because there is no atmosphere on the moon, the heat capacity and thermal conductivity of lunar materials are very low, so the temperature difference between day and night on the surface of the moon is very large. During the day, the temperature where the sun shines vertically is as high as+127℃; The temperature can be reduced to-183℃ at night. These values only represent the temperature on the surface of the moon. The temperature of lunar soil can be measured by radio observation. This measurement shows that the temperature in the deeper part of the lunar soil rarely changes, which is precisely due to the low thermal conductivity of lunar material. From the propagation of lunar seismic waves, we know that the moon also has layered structures such as shell, mantle and core. The outermost lunar shell is 60 ~ 65km thick. Under the lunar crust to the depth of 1000 km is the lunar mantle, which accounts for most of the lunar volume. Below the lunar mantle is the lunar core. The temperature of the lunar nucleus is about 1000℃, which is probably in a molten state. It is speculated that it may be composed of iron, nickel, sulfur and eclogite.
primary data
The average orbital radius of Apollo moon landing photos (19) is 38,4401km, the orbital eccentricity is 0.0549, the perigee distance is 363300km, and the apogee distance is 405. 500-kilometer average period of revolution 27.32 days average revolution speed 1.023 km/s orbital inclination varies between 28.58 and 18.28. Ascending node right ascension 125.08 perigee radial angle 3 18. 15 mo Dong Zhang1September; the average distance is 384,400km. Intersection regression period/kloc-0 18.66438.606666666.6, Sharo period18165436s2 (Earth 1/6), escape speed 2.38km/s, rotation period 27 days, 7 hours and 43 minutes/s.
Apparent magnitude at full moon-12.74 surface temperature (T) -233~ 123℃ average 23℃ atmospheric pressure1.3×10-10 kpa monthly period: name value (unit: day). 582 Relative to the perigee of vernal equinox, 27.554.550 relative to perigee and 27.2 12.220 relative to ascent, the diameter of the moon is 1/4 of the average diameter of the earth, and its mass is only 1/8 1 of the earth.
zone
The name crater was given by Galileo. It is a remarkable feature of the lunar surface, covering almost the whole lunar surface. The largest crater is Bailey crater near the South Pole, with a diameter of 295 kilometers, which is a little larger than Hainan Island. A small crater may even be a hole of dozens of centimeters. There are about 33,000 with a diameter of not less than 65,438+000m m. It accounts for 7%- 10% of the lunar surface area. A Japanese scholar put forward the classification of craters in 1969, which can be divided into Cravey type (ancient craters are generally unrecognizable, and some are surrounded by mountains), Copernicus type (young craters often have "radial lines", and the inner wall generally has concentric sections and a central peak), Archimedes type (the ring wall is low, which may have evolved from Copernicus type). There are two theories about the formation of craters: "impact theory" and "volcano theory". "impact theory" refers to the impact of other planets on the moon and the craters that human beings see now. "Volcano theory" means that there are many volcanoes on the moon, which finally broke out and formed craters. However, today's scientists advocate the "impact theory". The dark part of the moon sea seen by the naked eye on the earth is actually a vast plain on the moon. Due to historical reasons, this misnamed name has been preserved. moon
There are 22 identified moon seas, and some landforms are called "moon seas" or "moon-like seas". Most of the 22 recognized ones are distributed on the front of the moon. Three in the back and four on the side. On the front, the area of the Moon Sea is slightly over 50%, of which the largest "storm sea" covers an area of about 5 million square kilometers, almost the total area of nine French countries. Most of the moon seas are generally round and oval, and most of them are surrounded by some mountains, but some seas are connected together. Besides the sea, there are five lakes with similar topography-Hu Meng, Dead Lake, Fox Xia, Qiuhu and Chun Hu, but some lakes are bigger than the sea. For example, Hu Meng has an area of 70,000 square kilometers, which is much larger than Qihai. The parts of the moon and the ocean that extend to the land are called "bays" and "swamps", and they are both distributed on the front. There are five bays: Luwan, Xiawan, Central Bay, Hongwan and Yue Mei Bay. There are three kinds of swamps: rotten swamps, popular swamps and dreamy swamps. In fact, swamps are no different from bays. The topography of the Moon Sea is generally low, similar to the basins on the earth. The moon sea is1-2km lower than the average moon horizon, and the southeast of the lowest sea is even 6000m lower than its surroundings. The albedo of the moon (a physical quantity to measure the ability to reflect sunlight) is also relatively low, so it looks darker. The land and mountains on the moon are called the moon land, which is generally 2-3 kilometers above the horizon of the moon sea. Because of the high albedo, it looks brighter. On the front of the moon, the area of the moon land is roughly equal to that of the moon sea, but on the back of the moon, the area of the moon land is much larger than that of the moon sea. Isotope determination shows that the moon and land are much older than the moon and ocean, and they are the oldest landforms on the moon. On the moon, in addition to many craters, there are some mountains similar to those on the earth. Mountains on the moon often borrow the names of mountains on the earth, such as Alps and Caucasus mountains. The longest mountain range is the Apennines, which stretches for 1000 km, but its height is only three or four kilometers higher than the moon horizon. There are also some steep peaks in the mountains, whose height was overestimated in the past. It is now believed that the height of most peaks is similar to that of the earth. 1994, American Clementine lunar probe concluded that the highest point of the moon is 8000m. According to the data obtained by Chang 'e-1, the highest point on the moon is as high as 9840 meters. On the moon, there are 6 peaks over 6000 meters, 20 at 5000-6000 meters, 80 at 3000-6000 meters, and 200 at 1000 meters. The mountains on the moon have a common feature: the slopes on both sides are asymmetrical, and the slopes on the seaward side are steep, sometimes cliff-shaped, while the other side is quite flat. In addition to the high mountains, there are four cliffs hundreds of kilometers long on the moon. Three of them stand out in the Moon Sea, also known as the "Moon Graben". Another main feature of the radiation pattern on the surface of the moon is that some young craters often have beautiful "radiation patterns", which is a bright belt extending in all directions with craters as the radiation point, and it passes through mountains, the moon sea and craters almost in a straight line. The length and brightness of radiation patterns are different, and the most striking one is the radiation pattern of Tycho crater. The longest one is as long as 1800 km, especially at full moon. Secondly, Copernicus and Kepler craters also have quite beautiful radiation patterns. According to statistics, there are 50 craters with radiation patterns. The reason for the formation of radiation pattern is still inconclusive. Essentially, it is closely related to the theory of crater formation. Nowadays, many people tend to say that meteorite impact may make high-temperature debris fly far on the moon, with no atmosphere and little gravity. Other scientists believe that the function of volcano is not ruled out, and the eruption of volcano may also form a flying radiation shape. Moon Gap There are many famous rift valleys on the earth, such as the Great Rift Valley in East Africa. There is also such a structure on the surface of the moon-those seemingly winding black cracks are the Moon Valley, and some extend for hundreds of meters to Qian Qian meters, with widths ranging from several kilometers to tens of kilometers. Most of those broad moon valleys appear on the flat land of the moon, while those narrow and narrow moon valleys (sometimes called moon streams) can be seen everywhere. The most famous Moon Valley is the Moon Valley connecting the Jade Sea and the Leng Hai Alps in the southeast of Plato Crater. It cut off the Alps on the moon, which is very spectacular. The photos taken from space are estimated to be 130 km long and 10- 12 km wide.
Volcano distribution
The surface of the moon is covered with a huge layer of basalt lava (volcanic lava). Early astronomers thought that the dark area on the surface of the moon was a vast ocean, so they called it "mare", which means "sea" in Latin. Of course, this is wrong. These dark areas are actually plain areas composed of basalt lava. In addition to basalt lava structure, there are other volcanic features in the dark area of the moon. For example, the most prominent are the winding grooves, black deposits, volcanic domes and volcanic cones on the surface of the moon. However, these features are not significant, only a small part of volcanic traces on the surface of the moon. Compared with the earth volcano, the moon volcano can be described as senile. Most lunar volcanoes are between 3 billion and 4 billion years old; Typical dark plain, 3.5 billion years old; The youngest lunar volcano has a history of 1 100 million years. In geological age, the earth's volcanoes belong to youth, generally less than 654.38+ 10,000 years old. The oldest rock formation on earth is only 390 million years old, and the oldest submarine basalt is only 2 million years old. The young earth volcano is still very active, but there are no signs of volcanic and geological activities on the moon recently, so astronomers call the moon an "extinct" planet. Most volcanoes on the earth are distributed in chains. For example, in the Andes, volcanic chains outline the edge of the lithospheric plate. The mountains on the island of Hawaii show the hot spots of plate activity. There is no sign of plate tectonics on the moon. Typical lunar volcanoes often appear at the bottom of huge ancient impact craters. Therefore, most of the dark areas of the moon are round in appearance. The edge of the impact basin usually surrounds mountains and dark areas. The dark areas of the moon mainly appear on the far side of the moon. Almost covers the area of 1/3 here. On the far side, the dark area accounts for only 2%. On the other side, the terrain is relatively high and the crust is thick. It can be seen that the main factors controlling lunar volcanism are surface height and crustal thickness. The gravity of the moon is only 1/6 of that of the earth, which means that the flow resistance of the lunar volcanic lava is smaller than that of the earth, and the lava travels more smoothly. This can explain why the surface of the dark area of the moon is mostly flat and smooth. At the same time, the smooth lava flow is easy to spread, thus forming a huge basalt plain. Coupled with the small gravity, the ejected volcanic ash fragments fall further. Therefore, the eruption of the lunar volcano only formed a wide and flat lava plain, not a volcanic cone similar to the shape of the earth. This is one of the reasons why no large volcanoes have been found on the moon. There is no dissolved water on the moon. The dark areas of the moon are completely dry. Water is the most common gas in the earth's lava, and it is one of the important factors that cause the strong eruption of the earth's volcanoes. Therefore, scientists believe that water shortage also has a great influence on lunar volcanic activity. Specifically, if there is no water, the eruption of the lunar volcano will not be so strong, and the lava may just rush to the ground calmly and smoothly.
Composition and resources
4.5 billion years ago, the surface of the moon was still a sea of liquid magma. Scientists believe that the mineral KREEP, which constitutes the moon, shows the chemical clues left by the magma ocean. KREEP is actually a component called "incompatible element" by scientists-substances that cannot enter the crystal structure are left behind and float to the surface of magma. For researchers, KREEP is a convenient clue to explain the volcanic history of the lunar crust and infer the frequency and time of the impact of comets or other celestial bodies. The lunar crust consists of many major elements, including uranium, thorium, potassium, oxygen, silicon, magnesium, iron, titanium, calcium, aluminum and hydrogen. When bombarded by cosmic rays, each element emits specific gamma radiation. Some elements, such as uranium, thorium and potassium, are already radioactive, so they can emit gamma rays by themselves. But whatever the reason, the gamma rays emitted by each element are different, and each element has its own unique spectral line characteristics, which can be measured by spectrometer. Until now, human beings have not made a comprehensive measurement of the abundance of moon elements. At present, the measurement of spacecraft is limited to a part of the moon. The moon is rich in mineral deposits. It is reported that there are more rare metals on the moon than on the earth. There are three main kinds of rocks on the moon. The first is the Moon Sea Basalt rich in iron and titanium. The second is plagioclase, which is rich in potassium, rare earth and phosphorus, mainly distributed in the lunar highlands; The third type is mainly composed of 0. 1 ~ 1 mm debris particles. Moon rocks contain all the elements and about 60 minerals on the earth, 6 of which are not found on the earth. The moon is extremely rich in mineral resources, and the most common element 17 on the earth is everywhere on the moon. Take iron for example. Only the sand 5 cm thick on the surface of the moon contains hundreds of millions of tons of iron, while the sand on the whole surface of the moon is 10 meter thick on average. The iron on the surface of the moon is not only extremely rich, but also convenient for mining and smelting. It is reported that the iron on the moon is mainly iron oxide, as long as oxygen and iron are separated; In addition, scientists have developed ways to make cement and glass from lunar soil and rocks. On the surface of the moon, the content of aluminum is also rich. The lunar soil is also rich in helium -3. Helium fusion using deuterium and helium -3 can be used as energy for nuclear power plants. This fusion does not produce neutrons, which is safe, pollution-free and easy to control. It can be used not only for ground nuclear power plants, but also for space navigation. It is reported that the content of helium 3 in lunar soil is estimated to be 7 15000 tons. For every ton of helium 3 extracted from lunar soil, 6300 tons of hydrogen, 70 tons of nitrogen and 1600 tons of carbon can be obtained. From the current analysis, due to the large reserves of Helium 3 on the moon, it is undoubtedly a timely help for the future energy shortage of the earth. Many space powers regard obtaining helium 3 as one of the important goals of developing the moon. There are 22 main moon seas on the surface of the moon. Except for the East China Sea, the Moscow Sea and the Zhihai Sea, which are located on the back of the moon (the side facing the earth), the other 19 moon seas are distributed on the front of the moon (the side facing the earth). There are a large number of lunar basalt in these lunar seas, and the volume of basalt filled in 22 seas is about 1, 0 10 km, and the lunar basalt is rich in titanium, iron and other resources. Assuming that the ilmenite content in Yuehai basalt is 8% or the titanium dioxide content is 4.2%, the total ilmenite resources in Yuehai basalt are about1.3×1015 ~1.9×10. Kryptonite is one of the three rock types in the lunar highlands, and it is named because it is rich in potassium, rare earth elements and phosphorus. Kryptonite is widely distributed on the moon. The kryptonite in the wind-blown ocean area rich in thorium and uranium elements is covered by late moon sea basalt, and the kryptonite is mixed to form blast furnace and uranium material, and its thickness is estimated to be 10 ~ 20km. The total resources of rare earth elements in Kripke rocks in storm ocean area are about 22.5 billion to 45 billion tons. Thorium and axes rich in Kripke rocks are also one of the important mineral resources for human beings to develop and utilize the moon resources in the future. In addition, there are abundant metallic mineral resources such as chromium, nickel, sodium, magnesium, silicon and copper on the moon.
sports
The moon is the closest celestial body to the earth, and its average distance from the earth is about 38440 1 km. Its average diameter is about 3476 kilometers, which is 3/ 1 1 of the earth's diameter. The surface area of the moon is 38 million square kilometers, which is not as big as that of Asia. The mass of the moon is about 735 billion tons, which is equivalent to 1/8 1 of the earth's mass, and the surface gravity of the moon is almost equivalent to 1/6 of the earth's gravity. The diameter of the surface of the moon is about 1/4 of the diameter of the earth. The volume of the moon is about 1/49 of that of the earth. However, the moon is far away from the earth at the rate of 13 cm per year. This means that the moon will leave us one day, but it will take billions of years.
Contribution to the earth
The birth of the moon has added many new things to the earth. 1, while the moon revolves around the earth, its special gravity attracts the water on the earth and moves with it, forming tides. Tides helped the early aquatic life of the earth to land. A long time ago, the temperature difference between day and night was large, and the temperature was between the boiling point and freezing point of water, which was not suitable for human habitation. The special influence of the moon brings us precious four seasons and reduces the temperature difference, so it is suitable for human habitation. The orbit of the moon The moon orbits the earth in an elliptical orbit. The great circle cut by this orbital plane on the celestial sphere is called "White Road". The ecliptic plane is neither coincident with the celestial equator nor parallel to the ecliptic plane, and its spatial position is constantly changing. The period is 173 days. The average inclination of the lunar orbit (ecliptic) relative to the earth orbit (ecliptic) is 5 09'. The rotation of the moon The rotation period of the moon around the earth is 27.438+066 days, which happens to be a sidereal moon, so we can't see the back of the moon. We call this phenomenon "synchronous rotation", which is almost a universal law in the satellite world. It is generally believed that it is the result of the long-term tidal action of planets on satellites. The libration is a wonderful phenomenon, which enables us to see 59% of the moon. The main reasons are as follows: 1. In different parts of the elliptical orbit, the rotation speed does not match the revolution angular speed. 2, the intersection of the white road and the equator. Interaction between the Earth and the Moon The Earth and the Moon revolve around each other, and two celestial bodies revolve around the same center of gravity at 1600 km below the surface. Does the earthquake have anything to do with the moon? This is a problem that has puzzled scientists for nearly a hundred years. Now, a joint research team composed of researchers from Japan Institute of Disaster Prevention Science and UCLA has finally confirmed that the gravity of the moon affects the tides of seawater. When the earth's crust changes abnormally and a lot of energy is accumulated, the gravity of the moon is likely to be the fuse of earthquakes between the earth's plates. 10 year1On October 22nd, the famous American magazine Science published their research results. The natural fluctuation of seawater is what people often call tide. When the moon reaches the nearest place to the earth (we call it perigee), the spring tide of Wang Shuo is even bigger than usual. At this time, the spring tide is called perigee Wang Shuo spring tide. Scientists have been speculating about the influence of tides on earthquakes for a long time, but so far no one has proved its global influence. In the past, only near the seabed or volcano did earthquakes and tides show obvious connections. The researchers found that the occurrence of earthquakes is closely related to the tidal pressure in fault layers, and violent tides exert enough pressure on shallow fault layers, which will lead to earthquakes. When the tide is high, reaching about 2-3 meters, 3/4 earthquakes will occur. The smaller the tide is, the fewer earthquakes will occur. Elizabeth Gotchland, the author of the article, said: "The gravity of the moon affects the ebb and flow of tides, and the earth itself is deformed under the influence of the gravity of the moon. Violent tides play a great role in the triggering process of earthquakes. Due to the pressure fluctuation caused by tides, the time of earthquakes will be advanced or postponed. " John Vida, another author of the article and a professor in the Department of Earth and Space Sciences at UCLA, said: "The cause of the earthquake is still a mystery, and this theory can be said to be one of the explanations. We found that the force generated by the change of sea level within a few meters will significantly affect the probability of earthquakes, which is a solid step for us to thoroughly understand the causes of earthquakes. " Gochilan et al. combined the calculation of tidal phase and tidal magnitude for the first time, and made statistical analysis of earthquake and tidal pressure data. The calculation method used is from seismologist Tanaka of Japan Institute of Earth Sciences and Disaster Prevention. From 1977 to 2000, Tanaka investigated the location and time of 2207 earthquakes called "reverse fault type" and their relationship with the gravity of the moon when the earthquakes occurred. The results show that the time of earthquake occurrence is highly related to the pressure of tide on the fault plane. When the fault is dislocated due to the gravity of the moon, more earthquakes will occur. Tanaka believes: "The gravity of the moon is only about one thousandth of the force that causes abnormal changes in the earthquake crust, but its role cannot be underestimated. It is the last force of the earthquake, which is equivalent to the last straw that crushed the camel. " Libra movement: Looking at the moon from the earth, the surface of the moon is not completely half of it, because the moon swings like a balance. Observers on the earth will feel that the moon swings back and forth in the north-south direction during its orbit around the earth, that is, it swings like a balance in the dimensional direction, which is called "zonal libration" with an angle range of about 6 degrees and 57 minutes; The phenomenon that the moon swings back and forth in the east-west direction, that is, longitudinally, is called "libration", and the swing angle reaches 7 degrees and 54 minutes. In addition to these two main kinds of libration, the moon also has Sunday libration and physical libration. The first three kinds of libration are not the moon swing, but the phenomenon caused by the change of the relative position between the observer and the moon. Only the physical balance is that the moon itself is swinging, and the swing amplitude is very small. Because the orbit of the moon is elliptical, when the moon is at perigee, its rotation speed can't keep up with the revolution speed, so we can see that the eastern part of the moon reaches 98 degrees east longitude. On the contrary, when it is at the apogee in the middle of the month, its rotation speed is faster than its revolution speed, so we can see that the western part of the moon passes through 98 degrees Darcy. This phenomenon is called Libra movement. Because the orbit of the moon is inclined to the equator of the earth, when the moon moves in the starry sky, the polar regions will shake about 7 degrees, which is called Libra movement. Furthermore, since the distance between the earth and the moon is only 60 times that of radius of the earth, if the observer observes the moon from sunrise to sunset, the observation point will have the displacement of the diameter of the earth, which can be seen in the area with the longitude of 1 degree. This phenomenon is called Libra movement.
Discuss the origin of the moon in this paragraph.
general situation
At present, there is no conclusion about the origin of the moon: there are roughly four schools of thought about the origin of the moon, but there is no conclusion.
Resonance hypothesis
This is the earliest hypothesis to explain the origin of the moon. As early as 1898, George Darwin, the son of the famous biologist Darwin, pointed out in the article Tides and Similar Effects in the Solar System that the moon was originally a part of the earth, but later, due to the rapid rotation of the earth, some substances on the earth were thrown out, forming the moon after leaving the earth, and the pit left on the earth is now the Pacific Ocean. This view was quickly opposed by some people. They think that it is impossible to throw such a big thing at the speed of the earth's rotation. Besides, if the moon was thrown out by the earth, then the material composition of the two should be the same. However, through the analysis of the rock samples brought back from the moon by Apollo 12 spacecraft, it is found that there is a great difference between them.
theory of capture