1. leap year is a year in which ordinary years are divisible by 4 and cannot be divisible by 100. (For example, 2004 is a leap year, and 190 1 is not. )
2. Leap year can be divisible by 400 in century year. (For example, 2000 is a leap year, 1900 is not. )
Second, the leap year calculation method
1, non-integer centenary: leap year is divisible by 4. (For example, 2004 is a leap year, and 200 1 is not. )
2, the whole hundred years: leap years can be divisible by 400. (For example, 2000 is a leap year, 1900 is not. )
3. For a year with a large number: If this year can be divisible by 3200 and 172800, it is a leap year. For example, 172800 is a leap year, and 86400 is not (because it can be divisible by 3200, but it cannot be divisible by 172800) (this is calculated on the basis of 365 days, a tropical year of 5h48'45.5'').
Extended data:
First, the method of judging the average year.
1. To judge whether a year is a leap year, you only need to look at the last two digits of the year. If the last two digits are divisible by 4, it is a leap year, otherwise it is not.
2. When the last two digits are all 0, we will look at the first two digits of the year; If the first two digits are divisible by 4, it is a leap year, and vice versa.
3. If the two digits at the end of 2004 are 04, it can be directly regarded as 1 digit. If this number is divisible by 4, it is a leap year, otherwise it is not.
Second, the causes of leap years
The period of the earth's orbit around the sun is 365 days, 5 hours, 48 minutes and 46 seconds (365.438+09 days), which is the tropic of cancer. The Gregorian calendar has an average of only 365 days a year, which is about 0.2422 days shorter than the tropical year, and the remaining time is about one day every four years. So 1 day is added at the end of February of the fourth year, making the calendar year of that year 366 days, and this year is a leap year.
The current Gregorian calendar has 97 leap years every 400 years. According to a leap year every four years, it will count as 0.0078 days per year on average, so after 400 years, it will count as 3 days.
So every 400 years, three leap years will be reduced. Therefore, the Gregorian calendar stipulates that when the year is a whole hundred, it must be a multiple of 400 to be a leap year; It is not a century year with multiples of 400, and even a multiple of 4 is not a leap year.
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