Hua Feng heard John Widta, another author of the article and a professor in the Department of Earth and Space Sciences at the University of California, Los Angeles, say: "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 forces generated by changes in sea level within a few meters can significantly affect the probability of earthquakes, which is a solid step towards a thorough understanding of the causes of earthquakes. ”

For the first time, Göchlan et al. combined the phase of the tide and the size of the tide, and performed a statistical analysis of seismic and tidal pressure data, using a method from Tanaka, a seismologist at the Institute of Earth Sciences and Disaster Prevention in Japan.

Tanaka investigated 2,207 interplate earthquakes with a magnitude of 5.5 or higher on the Richter scale from 1977 to 2000, and the relationship between them and the gravitational pull of the moon at the time of the earthquake.

Tanaka said: "The gravitational pull of the moon is only about one-thousandth of the force that causes abnormal changes in the earth's crust where earthquakes occur, but its role cannot be underestimated, and it is the last help for earthquakes, which is equivalent to the last straw that crushes the camel." ”

A lunar eclipse is a special astronomical phenomenon. When the Moon travels behind the Earth's shadow, the sun's rays are obscured by the Earth.

In other words, the Sun, Earth, and Moon happen to be (or almost) in the same straight line at this time, so the light from the Sun to the Moon will be obscured by the Earth.

In the case of the Earth, when a lunar eclipse occurs, the Sun and Moon will differ by 180°. It should be noted that since the orbits of the Sun and the Moon in the sky (called the ecliptic and white paths) are not in the same plane, but have an angle of about 5°, only if the Sun and the Moon are near the two intersections of the ecliptic and the white path, respectively, will have a chance to join in a straight line and produce a lunar eclipse.

Lunar eclipses can be divided into two types: partial lunar eclipses and total lunar eclipses (there is no annular lunar eclipse because the Earth is larger than the Moon). A partial lunar eclipse occurs when only part of the Moon enters the Earth's umbra, and a total lunar eclipse occurs when the entire Moon enters the Earth's umbra. As for the penumbral lunar eclipse, it means that the moon only passes over the penumbra of the earth, causing a very slight decrease in the brightness of the lunar surface, which is difficult to see with the naked eye, so it is not noticed.

The diameter of the Moon is about 3,476 kilometers, about 1/4 of the Earth. In the orbit of the Moon, the diameter of the Earth's umbra is still 2.5 times that of the Moon. Therefore, when the center of the Earth and the Moon are roughly in the same straight line, the Moon will completely enter the Earth's umbra, resulting in a total lunar eclipse.

And if only part of the Moon is always obscured by the Earth's umbra, that is, only part of the Moon enters the Earth's umbra, a partial lunar eclipse occurs. There will be no annular lunar eclipse on the Moon because the Moon is much smaller than the Earth.

The diameter of the Sun is much larger than that of the Earth, and the Earth's shadow can be divided into umbra and penumbra. If the Moon enters the penumbra, so can the Sun's light

To be obscured somewhat, this phenomenon is astronomically known as a penumbral lunar eclipse. Since the sunlight is still very strong in the penumbra, the luminosity of the lunar surface is only slightly reduced, and in most cases the penumbral lunar eclipse is not easy to distinguish with the naked eye. Under normal circumstances, it is not called a lunar eclipse because it is not easy for people to find, so there are only two types of lunar eclipses: total lunar eclipses and partial lunar eclipses.

In addition, since the Earth's umbra is much larger than the Moon, this also means that in the event of a total lunar eclipse, the Moon will completely enter the Earth's umbra zone, so there will be no such phenomenon as an annular lunar eclipse.

Lunar eclipses generally occur twice a year, with a maximum of 3 occurrences and sometimes none at all. Because in general, the Moon either passes above or departs below the Earth's umbra, rarely passing through or partially passing through the Earth's umbra, so a lunar eclipse generally does not occur.

According to the statistics of observational data, the percentages of penumbral lunar eclipses, partial lunar eclipses, and total lunar eclipses in the middle of each century are about 36.60%, 34.46% and 28.94%.

The surface of the moon has dark parts and bright areas, the bright areas are highlands, and the dark areas are low-lying areas such as plains or basins, which are called lunar lands and moon-seas, respectively. When early astronomers looked at the moon, they thought that the dark areas were covered with seawater, so they called them "seas".

The famous ones are the sea of clouds, the wet sea, the still sea, etc. The bright part is the mountains, which are dotted with craters, or craters, which are low-lying forms of annular uplifts. There are more than 33,000 impact craters on the Moon with diameters greater than 1,000 metres. The Bailey crater, located near Antarctica, is 295 kilometers in diameter and could fit the entire island of Hainan. The deepest mountain is the Newton impact crater, which is 8,788 meters deep. In addition to impact craters, there are also ordinary mountains on the lunar surface. Mountains and deep valleys are stacked on top of each other, creating a unique scenery.

The structure of the far side of the moon is quite different from the front side. The Moon Sea occupies less area and has more impact craters. The terrain is uneven, undulating, and the longest and shortest lunar radii are located on the far side, with some places 4 km longer than the average lunar radius and others 5 km shorter (such as the Van der Graaf Depression). No "mass tumor" was found on the back. The back of the moon crust is thicker than the front one, up to 150 kilometers at its thickest point, while the front moon crust is only about 60 kilometers thick.

The name crater was given by Galileo. It is a distinctive feature of the lunar surface, covering almost the entire lunar surface. The largest impact crater is the Bailey crater near Antarctica, with a diameter of 295 kilometers, a little larger than Hainan Island. The small crater may even be a pothole of a few tens of centimeters. There are about 33,000 of them with a diameter of not less than 1,000 meters. It occupies 7%-10% of the surface area of the moon.

In 1969, a Japanese scholar proposed a classification method for impact craters, which are divided into clavi type (ancient impact craters, generally unrecognizable, some impact craters have a central peak) Copernican impact crater (young impact craters, often have impact action to cause a large number of rocks on the surface of the moon to sputter around, and a large number of rock fragments sputtered out of the sputtering are ejected and rolled on the lunar surface at high speed, changing the original topography of the lunar surface and the structure and color of the surface soil, forming obvious "radiation lines") , the inner wall generally has concentric circles of segment mounds, and the center generally has a central peak. Archimedes (low ring walls, probably evolved from Copernicus) bowl or dimple (small impact craters, some less than 3 m in diameter).

The dark part of the lunar surface that humans on Earth see with the naked eye is actually a vast plain on the lunar surface. For historical reasons, this misnamed name has been preserved.

There are 22 moon seas that have been identified, and there are also some terrains called "moon seas" or "moon seas". The vast majority of the recognized 22 are located on the front side of the moon. There are 3 on the back, 4 in the marginal area. On the front of the lunar sea is slightly more than 50% of the area, the largest of which is the "storm ocean" with an area of about five million square kilometers, almost the area of nine Frances combined.

Most of the moon seas are roughly circular or oval in shape, and are mostly enclosed by mountains, but some seas are connected. In addition to the "sea", there are five "lakes" with similar topography - Dream Lake, Dead Lake, Summer Lake, Autumn Lake, and Spring Lake, but some lakes are larger than the sea, such as Dream Lake with an area of 70,000 square kilometers, which is much larger than the sea of steam. The part of the Moon Sea that extends to the land is called "bay" and "swamp", both of which are distributed on the front. There are five bays: Luwan, Summer Bay, Central Bay, Hongwan, and Meiyue Bay, and there are three marshes: Rotten Swamp, Plague Swamp, and Dream Swamp, but in fact, there is no difference between Swamp and Bay.

The Moon Sea is generally low, similar to the basins on Earth, with the Moon Sea 1-2 km below the average level of the Moon, and the lowest sea, such as the southeastern part of the Rain Sea, even 6,000 m lower than the surrounding area. The lunar surface also has a lower albedo (a physical measure of the ability to reflect sunlight), making it appear darker.

The area above the lunar surface is called lunar land, which is generally 2-3 kilometers above the lunar sea level, and appears to be brighter because of its high albetry. On the front side of the Moon, the area of the lunar land is roughly equal to that of the lunar sea, but on the far side of the moon, the area of the lunar land is much larger than that of the lunar sea. From isotope determination, it is known that the lunar land is much older than the lunar sea and is the oldest topographic feature on the moon.

On the Moon, in addition to the numerous impact craters of the canine's teeth, there are also some mountains similar to those on Earth. The mountains on the moon are often named after the mountains on the earth, such as the Alps, the Caucasus, etc., the longest of which is the Apennines, which stretches for 1,000 kilometers, but the height is only three or four thousand meters higher than the level of the lunar sea.

There are also some steep peaks in the mountains, and their height was overestimated in the past. Most peaks are now considered to be about the same height as Earth's peaks. In 1994, the Clementine lunar probe of the United States came to the conclusion that the highest point of the moon is 8,000 meters, and according to the data obtained by Chang'e-1, the highest peak on the moon is as high as 9,840 meters. There are 6 peaks above 6,000 meters on the lunar surface, 20 peaks above 5,000-6,000 meters, 80 peaks at 3,000-6,000 meters, and 200 peaks above 1,000 meters.

A common feature of the mountains on the moon is that the slopes on both sides are very asymmetrical, with the seaward side being very steep, sometimes cliff-like, and the other side being quite gentle. This is due to the high-speed impact of small celestial bodies on the lunar surface, and the powerful impact energy makes the rocks on the surface of the moon vaporize, melt, break and sputter, digging a huge impact crater or impact basin, and the huge impact energy of the impact body produces a series of faults and cracks at the bottom of the impact crater, inducing the eruption and overflow of basalt magma inside the moon, forming a dark moon sea basin. The various sputtered materials that were ejected from the impact crater landed at different distances around the outer lunar perimeter, forming a gentle slope on the western side of the lunar perimeter.

In addition to mountains and mountain groups, there are four cliffs on the surface of the moon that are hundreds of kilometers long. Three of them protrude into the moon sea, and these cliffs are also called "moon moats".