Why do you rarely see leap December, leap January and leap February in the lunar calendar?

In the traditional Chinese lunar calendar, when the length of the first lunar month (29.5306) is the average of 1 month, that is, 12 months in a year and the length of the tropical year (365.2422) is about 10 and 2 1 day, it is necessary to set a leap.

In the six-year calendar in ancient China, the leap month method was adopted, with three years 1 month, five years and two months, and 19 years and seven months. Every month in a leap year is called "leap month". The leap month is placed at the end of the year. For example, the seal script used in the early years of the Qin Dynasty and the Western Han Dynasty started in October and ended in September. Leap month is placed after September, which is called "post-September".

When the taichu calendar Law was enacted in the early years of the Western Han Dynasty, leap months were inserted in every month of the year, and it was stipulated that lifeless months were regarded as leap months, and the month sequence was still the month sequence of last month, so long as it was called "leap months". This leap rule is the most reasonable in a smooth calendar.

In the Qing dynasty, the constitution continued, and it was changed into a fixed-atmosphere calendar. If we continue to simply follow the rule that there is no central leap, it is possible to set up two leap months a year. Therefore, the leap year is defined as 13 months between two winter solstices, and the first month of a leap year is defined as leap month. This rule has been in use ever since.

Therefore, in leap years, April, May and June are the most, September and October are the least, and November, December, January and February will not appear, at least for thousands of years.