Why did the general contractor include "solar terms" and "neutral atmosphere" in the first month?

Calendars are divided into three types: solar calendar, lunar calendar and yin-yang calendar. The solar calendar is divided according to the movement cycle of the sun, and there is a leap year phenomenon. It is fixed in February, one day more than the normal year, that is, 29 days.

In the lunar calendar, the profit and loss cycle of the moon is one month, and the product of 12 months is one year. If we don't consider the movement law of the sun, it can't show the warmth and coldness of the four seasons.

The lunar calendar in China is the lunar calendar, with the month of the lunar calendar as the month and the year of the solar calendar as the year. According to the lunar calendar, the big month is 30 days, the small month is 29 days, and a year is 12 months, totaling 354 or 355 days, which is about 1 1 day less than the return, and one month less than the accumulated four years. In order to solve this problem, leap is added.

According to the China lunar calendar, a month without "neutral qi" is a leap month. Ancient astronomers called odd numbers of the 24 solar terms solar terms and even numbers neutral. There are 12 solar terms and 12 neutral gases in a year, and it is stipulated that 12 months of the lunar calendar should be marked with 12 neutral gases. For example, it must rain in the first month and in the second month.

The reason why there will be no neutral gas for one month is because the 24 solar terms are determined according to the solar calendar, and the neutral gas determined according to the solar calendar will be delayed by one day every month in the lunar calendar. When it is postponed to the end of the month, there will be only solar terms and no neutral gas next month. This is the truth of leap July this year.

In order to keep the return year of the lunar calendar in sync with the Gregorian calendar, the ancients adopted the method of setting leap months. Leap for one month every three years, two months every five years, 19 leap for seven months. A year with a leap month is called a leap year.

The exact month of leap year is determined by 24 solar terms. The ancient calendar has 24 solar terms, which are divided into solar terms and neutral solar terms. There are two kinds of gases in the lunar calendar every month. The beginning of the month is called the solar term, and the middle of the month is called the gas. Even-numbered solar terms among the 24 solar terms, namely, rain, vernal equinox, Grain Rain, Xiaoman, summer solstice, great heat, summer equinox, first frost, light snow, winter solstice and great cold, are also called "Zhong Qi". "For example, beginning of spring is the first month of the solar term, and the rain is the gas of the first month." The first month of leap year is neutral, that is, this year's leap month.

The average length of the two solar terms in Gregorian calendar is 30.5 days, while that in Lunar calendar is only 29.5 days, with a difference of 1 day. Therefore, the monthly gas consumption will be 1-2 days later than last month. If this goes on, there will always be a month when there is only solar terms and no gas. This non-neutral month is defined as "leap month" by the calendar and is called "leap month". This year, the summer in Xu Bing falls on July 30th of the lunar calendar, and the autumnal equinox falls on the second day of next month. There is only one white dew in the middle of the month, so this month is a leap month this year. Leap month is after July, so this year is leap July.

Then why is there no leap month? This is because the earth's orbit around the sun is an ellipse, and the sun is located at a focus of the ellipse. In a year, the distance between the earth and the sun is getting closer and farther. When the earth is far away from the sun, it moves slowly around June in Gregorian calendar, so the interval between the two gases is longer, exceeding 3 1 day at the longest. According to the average length of the previous 30.5 days, there is a great possibility that there is no gas in the middle of the month and there is a great possibility of a leap month. So there are many opportunities in leap April, leap May and leap June.

Around 65438+February in Gregorian calendar, the earth moves fast and the neutral gas interval is short. The shortest time is only a little more than 29 days, which is shorter than a month in the lunar calendar. Therefore, the first month, November and twelfth month are unlikely to be neutral. On the other hand, there are fewer opportunities for leap months.