What are the reasons why April and leap April appear in the lunar calendar?

The working people in ancient times called the previous solar terms (beginning of spring, Jing Zhe, Qingming, Long Summer, Mang Zi, Xiaoshuhu, beginning of autumn, Bailu, Cold Dew, beginning of winter, Heavy Snow and Slight Cold) "solar terms". The last solar terms (rain, vernal equinox, Grain Rain, Xiaoman, Summer Solstice, Great Summer, Early Summer, Autumn Equinox, Early Frost, Light Snow, Winter Solstice and Great Cold) are called "Zhongqi". The average value between two neutral gases is 365.2422÷ 12=30.4368 days, then 30 or 3 1 day. The earth's orbit around the sun is elliptical and moves slowly at the perihelion (vernal equinox and autumnal equinox), and the interval between the two solar terms can reach 3 1.45 days. On the other hand, the average lunar new moon is only 29.5306 days, including 29 days in the first lunar month and 30 days in the second lunar month. In this way, there will be such a situation: in some months (usually abortion), the last breath has passed at the beginning, and the next breath has not come at the end. For example, 200 1 (New Year's Eve) is May 21(April 29), and the first day of the next lunar month is May 23. However, this lunar month ends on June 20, and the summer solstice is June 2 1, so this lunar month is not "neutral", it falls in the fourth month of the lunar calendar. According to this leap law, it will leap in July 2006, May 2009, April 20 12, September 20 14, June 20 17 and April 2020.

Some can also be calculated:

Calculation of leap month in lunar leap year, three-year leap, five-year leap, 19 leap; The lunar calendar basically takes 19 as a cycle, corresponding to the same time in the Gregorian calendar. For example, in the Gregorian calendar, May 27th, 2006, 5438+0, May 27th 1982 and May 27th 1963 are the fifth day of leap April.

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