When is February a leap month? How is it calculated?

In the calendar, the Gregorian calendar appears on February 29th every four years, which is a leap February. There are two February in the lunar calendar year, and the second February is a leap February.

Examples of years: 2004 (Shen Jianian), 2023 (Guimao Year), 2042 (Ren Xunian) and 2099 (years that have not passed yet).

Leap month calculation:

The mid-year month of the lunar calendar is based on the length of the first month of the lunar calendar of 29.5306 days, so the big month is 30 days and the small month is 29 days. In order to ensure that the first day of each month is a new moon, the arrangement of large and small months is not fixed, but needs to be determined through strict observation and calculation.

Extended data

Related background:

The solar calendar is also called the solar calendar, and the tropic year is the basis of the calendar. Since the tropic year is equal to 365.2422 average solar days (that is, 365 days, 5 hours, 48 minutes and 46 seconds), it is not a whole day.

Therefore, the solar calendar takes 365 days as the average year, that is, the "average year". In order to eliminate the gap between it and the actual tropic year, the solar calendar has increased by 97 days in 400 years by "setting leap"; Or add one day in February every four years, which is the "leap year" of the solar calendar and the "leap February" of the solar calendar.

Lunar calendar is different. In fact, it is a kind of "yin and yang calendar", which is the same as the lunar calendar and similar to the solar calendar. It is based on the moon's profit and loss cycle as the calendar month, and also takes into account the annual solar terms.

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