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

Feb. 29 is more than just an extra day we have once every four years. There is some science behind it. Here's how leap days ...

A calendar notation in which the date is represented by one number. For example, the Julian date for December 11, 1942 is 2430705; while December 12, 1942 is 2430706. The Julian date is widely ...

Prior to the Gregorian and even Julian calendars ... emperor adopted a 365-day calendar and added 10 days the calendar, including a leap day in February every four years, calendar.com said.

4 Leap years were introduced by the Roman emperor Julius Caesar, who created a new calendar to take the extra quarter-days into account. The Julian calendar ... the exact date on which this ...