How to calculate leap year?

The establishment of leap year is to make up for the time difference between the number of days in a year and the actual period of revolution of the earth caused by man-made calendar regulations, and the year to make up for the time difference is leap year. Leap year has 29 days in February and 366 days in the whole year, which is divided into ordinary leap year and century leap year. Ordinary leap year means that the Gregorian calendar year is a multiple of 4, not a multiple of 100, but the leap year must be a multiple of 400.

The most fundamental reason is that the time for the earth to orbit the sun once is 365 days, 5 hours, 48 minutes and 46 seconds, which is about 365 days, but the average year of the Gregorian calendar is only 365 days, which is about 0.2422 days less than the time for the earth to orbit the sun once, and the remaining time is about one day every four years. Therefore, one day added at the end of February of the fourth year is the Gregorian calendar year of that year. Then this year is called leap year. In the current calendar, there are 97 leap years every 400 years. Calculated by a leap year every four years, it will be 0.007 8 days per year on average, so after more than 400 years, it will be about 3 days together, and then 3 leap years will be reduced every 6.5438+million years. Therefore, when a year is a whole hundred years, it must be four thousand years.

As a kind of China lunar calendar, the number of days per month depends on the monthly loss. The time of a year is 12 months, and the average annual proportion is about 1 1 day. In order to close the earth's orbit around the sun, that is, the tropic year, every 2-4 years, a month is added as a leap month, and the month added in a leap month is subject to the lunar calendar.

Generally speaking, this is an idea that ancient ancestors calculated the errors with modern people in a scientific way according to their own calculation methods to make up for these errors.