What is there to know about the moon?

The moon is also called Taiyin, commonly known as the moon. It is the earth's only natural satellite. The celestial body closest to the earth is also the most thoroughly studied celestial body. It is the only celestial body that humans have visited in person so far. The Moon is the most obvious example of a natural satellite. In the solar system, except for Mercury and Venus, all other planets have natural satellites. The moon is approximately 4.6 billion years old. The moon has a layered structure such as crust, mantle, and core. The average thickness of the outermost lunar crust is about 60-65 kilometers. Below the lunar crust to a depth of 1,000 kilometers is the lunar mantle, which accounts for most of the moon's volume. Below the lunar mantle is the lunar core. The temperature of the lunar core is about 1,000 degrees, and it is likely to be in a molten state. The diameter of the moon is about 3476 kilometers, which is 3/11 of the earth and 1/400 of the sun. The moon's volume is only 1/49 of the Earth's, and its mass is about 735 billion tons, which is equivalent to 1/81 of the Earth's mass. The gravity on the moon's surface is almost 1/6 of the Earth's gravity. The moon's surface has dark parts and bright areas. When early astronomers observed the moon, they thought that the dark areas were covered with sea water, so they called them "sea". The famous ones include the Sea of ??Clouds, the Sea of ??Shit, the Sea of ??Tranquility, etc. The bright part is the mountains, where there are many mountains, criss-crossing mountains, and dotted craters everywhere. Bailey Crater, located near the South Pole, has a diameter of 295 kilometers and can fit the entire Hainan Island into it. The deepest mountain is Newton Crater, which is 8,788 meters deep. In addition to craters, there are also ordinary mountains on the moon. Mountains and deep valleys overlap, creating a unique scenery. Map of the far side of the moon. The front side of the moon always faces the earth. The reason is the long-term effect of tides. On the other side, most of the far side of the moon cannot be seen from the Earth, except for the area near the edge of the moon that is visible in the middle due to the movement of the scales. In the era before detectors, the far side of the moon has always been an unknown world. One of the distinctive features of the far side of the Moon is that there are almost no darker lunar surface features such as maria. When the man-made probe moves to the far side of the moon, it will not be able to communicate directly with the earth. The moon orbits the Earth once in about one lunar month, and moves half a degree relative to the background starry sky every hour, which is approximately the same as the apparent diameter of the moon. Unlike other satellites, the Moon's orbital plane is closer to the ecliptic plane than to the Earth's equatorial plane. Relative to the background starry sky, the time it takes for the Moon to orbit the Earth (moon revolution) once is called a sidereal month; and the time it takes for a new moon to the next new moon (or between two identical moon phases) is called a synodic month. The synodic moon is longer than the sidereal moon because the earth itself advances a certain distance in its orbit around the sun during the moon's orbit. Because the moon's rotation period is exactly the same as its revolution period, the earth can only see the same side of the moon always facing the earth. Since the early formation of the Moon, the Earth has been subject to a torque that causes its rotation to slow down. 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 moves away from the Earth at a speed of about 38 millimeters per year. At the same time, the Earth's rotation is getting slower and slower, and the length of the day is getting longer by 15 microseconds every year. The gravitational pull exerted by the moon on the earth is one of the causes of tides. The Moon's orbit around the Earth is a synchronous orbit, and the so-called synchronous rotation is not strictly enforced. Since the moon's orbit is elliptical, when the moon is at perigee, its rotation speed cannot keep up with its revolution speed. Therefore, we can see the area on the eastern side of the moon reaching 98 degrees east longitude. On the contrary, when the moon is at apogee, its rotation speed is faster than its revolution speed. , so we can see the area in the western part of the moon reaching 98 degrees west longitude. This phenomenon is called meridian movement. Supplement: The moon itself does not emit light, it only reflects sunlight. The brightness of the moon changes 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. The brightness of the full moon averages -12.7 magnitude (see). The average illumination it gives to the earth is 0.22 lux, which is equivalent to the illumination of a 100-watt electric lamp at a distance of 21 meters. The moon is not a good reflector. Its average albedo is only 7%, and the remaining 93% is absorbed by the moon. The albedo of the lunar maria is even lower, about 6%.

The lunar highlands and craters have an albedo of 17%, making the mountains appear brighter than the maria. The brightness of the moon changes accordingly, and the brightness of the full moon is more than ten times greater than that of the first and second quarters. Since there is no atmosphere on the moon, and the heat capacity and thermal conductivity of the lunar surface materials are very low, the temperature difference between day and night on the lunar surface is very large. During the day, the temperature is as high as 127°C in places where the sun shines vertically; at night, the temperature can drop to -183°C. These values ??only represent the temperature of the moon's surface. The temperature in the lunar soil can be measured using radio observations. This measurement shows that the temperature in the deeper layers of the lunar soil rarely changes. This is due to the low thermal conductivity of the lunar material. From the propagation of moon shock waves, we know that the moon also has a layered structure such as crust, mantle, and core. The outermost lunar crust is 60 to 65 kilometers thick. Below the lunar crust to a depth of 1,000 kilometers is the lunar mantle, which accounts for most of the moon's volume. Below the lunar mantle is the lunar core. The temperature of the lunar core is about 1,000°C, and it is likely to be molten. It is speculated that it is composed of Fe-Ni-S and eclogite materials.