How to calculate leap April?

Twenty-four solar terms are calculated according to beginning of spring, odd numbers are called "solar terms" (beginning of spring, Jing Zhe, Qingming, Long Summer, Mangzhong, Xiaoshu, beginning of autumn, Bailu, Cold Dew, beginning of winter, Heavy Snow and Slight Cold), and even numbers are called "Zhongqi" (Rain, Equinox, Grain Rain, Xiaoman, Summer Solstice, Big Tree, Early Tree and Autumn Equinox).

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 it runs very fast at the perihelion (vernal equinox and autumnal equinox), and the maximum 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 (Xinsi year of the snake), Xiaoman is May 2 1 (April 29th of the lunar calendar), and the first day of the next lunar month is May 23rd. However, this lunar month ends on June 20, and the summer solstice falls on June 2 1 day, so this lunar month is not "neutral", but in.

According to this leap rule, it will leap in July 2006, May 2009, April 20 12, September 20 14, June 20 17, April 2020 and February 2023.

Extended data:

Around 2 1 century, leap April is a common leap month, which usually occurs once every 8 years or 1 1 year, and once every 38 years at the longest, and the frequency is second only to leap May. However, the law is not static. As time goes on, the frequency of leap April is gradually decreasing. The latest year of Dragon Boat Festival is usually in April.

In the China lunar calendar, a year with a leap month is called a leap month year. The lunar year is usually 12 months, 354 or 355 days, and only a few years have only 353 days (for example, 1965). The leap month year is 13 months, which is 384 days in general, 383 days in some years and 385 days in very few years (such as 2006). As a kind of lunar calendar, the number of days in each month depends on the monthly loss, and the time of one year is based on 12 months. In order to close the earth's cycle around the sun, that is, the tropic year, one month is added every two to three years, and the added month is a leap month, so the leap year of the lunar calendar is 13 months.