The Julian calendar has two types of years: a normal year of 365 days and a leap year of 366 days. They follow a simple cycle of three normal years and one leap year, giving an average year that is ...

In the Julian calendar, the extra day was not February ... So, every four hundred years, three leap years must be designated non-leap. The Gregorian calendar thus adopted the following rule.

The extra day, known as a leap day, is Feb. 29, which does not exist in non-leap years ... and his successor Augustus.) The Julian calendar included leap years every four years without exception ...

The Gregorian calendar, introduced in 1582, replaced the Julian calendar to correct its inaccuracies, particularly the overly frequent leap years This change required skipping several days to realign ...