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

However, the Julian calendar was not perfect, since it introduced a delay of about one day every 128 years to the solar year. Therefore, since 1582, we have been governed by the Gregorian calendar ...

Meanwhile, while the former group - which is the most common and includes nations like the UK, France, Spain and Germany - also originally used the Julian calendar, they changed to the Gregorian ...

For example, the Julian date for December 11 ... 3268. Contrast with "Gregorian date," which is the common calendar notation of month, day and year. THIS DEFINITION IS FOR PERSONAL USE ONLY.

Catholic and Orthodox — fall on the same date, April 20, due to the alignment of the Julian and Gregorian calendars.

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 ...

Presidents Day is a federal holiday celebrated each year in mid-February to honor past U.S. presidents. Locally, it's part of ...

It is marked as January 1 in the Julian calendar, which was used before the Gregorian calendar. Some countries, including Italy, Poland, Portugal, and Spain, accepted the Gregorian calendars ...