Gregorian calendar on February 30th

The reason why the lunar calendar decides whether a month is 30 days or 29 days is to ensure that the moon is the roundest on 15 every month, which requires astronomical calculation to decide which month is 30 days or 29 days, so the size of the lunar calendar is not as fixed and irregular as the Gregorian calendar.

The lunar calendar uses a combination of yin and yang instead of a simple lunar calendar. Observe the change of the moon phase to determine the month (lunar calendar), and observe the regression change of the sun to determine the 24 solar terms (solar calendar). In the lunar calendar, the change process of the moon "lack (new moon)-full moon (full moon)-lack (dark moon)" is defined as "lack of the moon", also known as "full moon". The average cycle is more than 29 days, so the big month is 30 days, the small month is 29 days, the lunar calendar is 12 months, and the whole year is 354 days or 355 days. February 30th is the lunar month, so it's not surprising that there are 30 days.

Pay attention to distinguish between February and Gregorian calendar here. The current Gregorian calendar (national calendar) is a calendar founded in the west and belongs to the solar calendar (the period of a year is about 365 days), but it neither reflects the return movement of the sun (the revolution of the earth) nor the change of the moon phase. The length of the month is artificially specified. Personally, it is conducive to economic activities and convenient settlement.

Gregorian calendar (Gregorian calendar) does not have February 30th, but lunar calendar does, but the size of lunar months is very irregular, sometimes it is two, three, four big months or two consecutive three small months, and the length of calendar years is also different, and there is a big gap. The distribution dates of solar terms and gas in the lunar calendar are very unstable and vary greatly.