What is a "leap month"? Why one more month?

Leaping month is a way of calendar leap, especially in the Chinese calendar (also known as lunar calendar), every leap year is added with one month.

For example, there will be thirteen months in the lunar year of rooster on 20 17, and the extra month is June, also called leap June.

The lunar calendar calculates the month according to the first month of the lunar calendar, that is, according to the profit and loss of the moon (because the moon revolves around the earth, it looks round and short). The moon from the waning moon to the full moon, and then from the full moon to the waning moon, is exactly a cycle. We call it a month.

The moon goes through this cycle for about 29 and a half days, so there are 29 small months and 30 big months in the lunar calendar. The whole year is about 354 days, which is about 1 1 day different from the tropical year. Less than return 1 1 day per year. Over time, the days will be less and less. In order to coordinate the contradiction between tropic year and Gregorian year and prevent the month of Gregorian year from being out of touch with tropic year and four seasons, 1 leap is set every 2 to 3 years.

Extended data:

The leap month in the Gregorian calendar is very regular, and there is a leap year every four years.

February of every leap year in Gregorian calendar is a leap month, which will be one day more than in the past three years. Generally, there are 28 days in February and 29 days in February of leap year. Therefore, it will take four years for friends who celebrate their birthdays on the Gregorian calendar to have a real birthday on February 29.

Before the Han dynasty, a year was about 365.25 days, but we often counted it as 365 years, and the other 0.25 days were ignored. But in the fourth year, four consecutive 0.25 days will be merged into one day, so there is a deviation in calculating another year as 365 days, so we record it as 366 days to fix this mistake. This is the calculation method of the Tropic of Cancer.

Reference source: Baidu Encyclopedia-Leap Moon