202 1 Is there a leap month?

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.

Therefore, it is common for two consecutive months to be big or small in the lunar calendar, and even there are rare exceptions such as March and April in 1990. September, 10,1month and1February are four consecutive months.

Extended data:

Because the average interval between two adjacent neutral gases (about 30.4368 days) is nearly 1 day longer than the average period of monthly phase change (about 29.5306 days), the date of the 24 solar terms in the lunar calendar is generally delayed month by month, so in some lunar months, neutral gases fall at the end of the month, and there is no neutral gas in the next month (that is, the next neutral gas is located at the beginning of the next lunar month).

Generally speaking, there will be one month without natural gas every two years or so (every 30 lunar months on average), which is consistent with the year when leap months are needed. Therefore, the lunar calendar stipulates that non-neutral months are leap months.