A century leap year is a

leap year A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) compared to a common year. The 366th day (or 13th month) is added to keep t ...

in the

Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...

that is evenly

divisible In mathematics, a divisor of an integer n, also called a factor of n, is an integer m that may be multiplied by some integer to produce n. In this case, one also says that n is a '' multiple'' of m. An integer n is divisible or evenly divisibl ...

by 400. Like all leap years, it has an extra day in February for a total of 366 days instead of 365. In the obsolete

Julian calendar The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts ...

, all years that were divisible by 4, including end-of-century years, were considered leap years. The Julian rule, however, adds too many leap days (about three extra leap days in 400 years), which resulted in the calendar drifting gradually with respect to the astronomical seasons. To remedy this,

Pope Gregory XIII Pope Gregory XIII (, , born Ugo Boncompagni; 7 January 1502 – 10 April 1585) was head of the Catholic Church and ruler of the Papal States from 13 May 1572 to his death in April 1585. He is best known for commissioning and being the namesake ...

introduced in 1582 a slightly modified version of the Julian calendar, the

, where century years are leap years only if they are divisible by 400. This eliminates three of the four end-of-century years in a 400-year period. For example, the years 1600, 2000, 2400, and 2800 are century leap years since those numbers are evenly divisible by 400, while 1700, 1800, 1900, 2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000 are

common year A common year is a calendar year with 365 days, as distinguished from a ''leap year'', which has 366 days. More generally, a common year is one without Intercalation (timekeeping), intercalation. The Gregorian calendar, used by the majority of ...

s despite being evenly divisible by 4. This scheme brings the average length of the calendar year significantly closer to the astronomical length of the year, nearly eliminating the drift of the calendar against the seasons. The Gregorian calendar was adopted by various countries at different times over several centuries. Dates prior to 1582 are generally recorded using the Julian calendar, and different countries have different conventions about how to record dates between 1582 and their adoption of the Gregorian calendar. Consequently, for example, the year 1700 was a leap year in the British and Russian empires but not in most of the rest of Europe; 1800 and 1900 were still leap years in the Russian Empire but not generally elsewhere.

Notes

References

External links

An Introduction to Calendars courtesy of the United States Naval Observatory

Units of time Calendars Gregorian calendar Leap years in the Gregorian calendar {{time-stub sv:Sekelskottår