What's a half moon like?

Half the moon is like a boat. The moon, the name of the celestial body, is called the moon as seen by the naked eye. In ancient times, it was also called Taiyin, Xuantu, Chanjuan and Pan Yu. It is a satellite of the earth and the fifth largest satellite in the solar system. The diameter of the moon is about a quarter of that of the earth, and its mass is about one-eighty-first of that of the earth. Its surface is covered with craters formed by the impact of small celestial bodies. The average distance between the moon and the earth is about 384,400 kilometers, which is about 30 times the diameter of the earth.

Lunar revolution

The moon moves around 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 cycle is 27.32 days. The average inclination of the lunar orbit (ecliptic) relative to the earth orbit (ecliptic) is 5 09'. But it is known that the moon gradually leaves the earth at an average speed of 3.8cm per year.

Moon rotation

The moon revolves around the earth and rotates at the same time, with a period of 27.438+066 days, which happens to be a sidereal moon, so we can't see the back of the moon. This phenomenon, which we call "synchronous rotation" or "tidal locking", is almost a universal law in the satellite world of the solar system. It is generally believed that it is the result of long-term tidal action of satellites on the planet. The libration is a wonderful phenomenon, which enables us to see 59% of the moon. There are mainly the following reasons:

(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.

The appearance of the moon moves half a degree per hour for the background starry sky, 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.