In the Gregorian calendar (Gregorian calendar), a year with leap days is called leap year, which is generally 365 days and 366 days. Because the earth's cycle around the sun is 365 days, 5 hours, 48 minutes and 46 seconds (365,438+09 days), which is the tropic year, the Gregorian calendar sets a year as 365 days.

The remaining time is about one day in four years, plus February, so the normal year is 365 days, February is 28 days, leap year is 366 days, and February is 29 days. So every 400 years, there are 97 leap years, with one day added at the end of February and 366 days in leap years.

Extended information of leap year and leap month in China lunar calendar.

On the lunar calendar in China, there are two versions of leap year and leap month. Generally speaking, there are 365 days in a year, and its accurate value is 365.2422 days in a year, which is 0.2422 days different from the actual situation. Four years later, these differences just constitute one day, which means that there are 366 days in the fourth year after four years, so the ancients stipulated this year as a leap year.

Leap month is because every leap year will have one more day, and the extra month will add up, so this year will have 13 months, so we call this year leap month year. Leaping moon is a phenomenon in the lunar calendar. This is a leap month. That year, there were 13 months in the lunar calendar, and that year was called leap month year.

Baidu encyclopedia-leap year