How long does it take for the moon to go around the earth?

The earliest calendar was made according to the change of the moon's round and round. The obvious profit and loss of the moon is an extremely obvious and accurate time period. People have long known the changing law of the moon.

While the earth keeps spinning, it also revolves around the sun. The Earth and the Moon are a celestial system-earth-moon system. The moon revolves around the earth and rotates at the same time. The moon's orbit around the earth is also an elliptical orbit, and the projection of this orbit on the celestial sphere is called the white road. The included angle between the ecliptic plane and the ecliptic plane is 5 09'. The moon also rotates, and the rotation period is the same as that of period of revolution.

The time for the moon to circle the earth is 27.32 17 days. This is called the sidereal moon, which is the real period of the moon's revolution, that is, the time interval between the moon passing through the earth twice and connecting with a star.

However, the moon not only goes around the earth, but also goes around the sun with the earth. The period from this full moon to the next full moon or from this new moon to the next new moon is 29.5306 days, which is called a new moon. This period is longer than the sidereal month.

About 5000 years ago, the Samaritans living in the Tigris and Euphrates rivers created the earliest calendar in the world according to the movement of the moon. They divide a year into 12 months with 30 days in each month. This method of calculating the date by using the moon's full and short periods is called "lunar calendar" and "lunar calendar".

But this "lunar calendar" has a big error and can't keep up with the movement of the moon. Later, the Babylonians changed the Samaritan calendar to alternate between 29 and 30 days a month, so that the months coincided with the running time of the moon. Babylonian astronomers even found that every 19 years, the sun and the moon have the same "phase relationship", that is, in 19 years, there are at most 7 leap months (30 days per month), so that the calendar keeps pace with the sun and the moon.

Many countries in the world have used the lunar calendar, and now most of them use the solar calendar. Some countries that believe in Islam still use the lunar calendar. It is also called Islamic calendar, Hijri calendar and Hijri calendar.

Taiyin is 354 days older, but it is 8 hours, 48 minutes and 36 seconds different from the actual length of 12 moons. If we listen to its development, its new year will no longer be a "new moon" in three years. Therefore, in order to solve this problem, we have arranged 355-day 1 1 leap year in 30 lunar years, and changed the 65438+February of leap year from small month to big month.

The lunar month in the hijri calendar is generally the same as the old calendar in China. However, the first day of each month is determined by the combination of the sun and the moon in the old calendar of our country, while it is determined by the first day of each month in the Gregorian calendar. This phenomenon appears in the second or third day of each month in the Chinese old calendar. Therefore, the first day of the hijri calendar is equivalent to the second or third day of the China Gregorian calendar.

The advantage of the lunar calendar is that the date coincides with the moon, from the new moon, the first quarter moon, the convex moon to the full moon, and then from the full moon to the concave moon, the second quarter moon and the waning moon to the new moon. Look at the moon's profit and loss to know the date. When people know the date of this day in the lunar calendar, they can calculate the time when the tides come and go, which occurs at noon and midnight. After that, the tide is getting smaller every day, and the interval between high tides is delayed by more than 40 minutes a day. This is conducive to coastal residents engaged in navigation, fisheries, flood control and other work.

The disadvantage of the lunar calendar is that it is biased towards the moon and ignores the sun, so it can't cope with the seasonal changes. The average lunar year is 354.366 days, which is shorter than the tropic year 10.8756 days. About every 32 solar years, there is one more lunar year in the hijri calendar. Therefore, festivals stipulated by Islam, such as Eid al-Adha, are often held in different months and seasons of the Gregorian calendar.

Such "lunar year" is only applicable to religious and ethnic activities and cannot meet the requirements of agricultural production. Therefore, people also use the solar calendar outside the Lunar New Year.