Uncommon
Calendar year
Period of time
Calendar year
A calendar year begins on the New Year's Day of the given calendar system and ends on New Year's Eve, and thus consists of a whole number of days. The astronomer's mean tropical year, which is averaged over equinoxes and solstices, is currently 365.24219 days. As this is not an integer, solar calendars have strategies to adjust for the 0.24219 remainder. Neither is it a whole number of lunar months (being about 10 or 11 days more than 12 lunations) so lunisolar calendars also must include adjustments to resynchronise with the seasons. Pure lunar calendars ignore the solar cycle and instead have an invariant year of twelve lunar months that drifts through the seasons. The Gregorian calendar year, which is in use as civil calendar in most of the world, begins on January 1 and ends on December 31. It has a length of 365 days in an ordinary year but, in order to reconcile the calendar year with the astronomical cycle, it has 366 days in a leap year. With 97 leap years every 400 years, the...
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