The modern calendar has Roman Catholic roots. As the sun does not adhere exactly to the earthly calendar, leap days are ...

For example, the Julian date for December 11 ... Contrast with "Gregorian date," which is the common calendar notation of month, day and year. THIS DEFINITION IS FOR PERSONAL USE ONLY.

The original Roman calendar divided the year from March to December into 10 months of either 29 or 31 days, based on lunar ...

Every four years, an extra day is added to the calendar, But even with leap day, the math doesn't exactly, well, math.

preferring instead to follow some of the traditions of the Julian calendar. So this sees islanders celebrate Christmas on 6 January rather than 25 December, and New Year's Day on 13 January.

Prior to the Gregorian and even Julian calendars, Roman King Numa Pompilius (715-673 BC) set about creating a calendar with equal-length months, the University of Chicago said. "When Numa ...