Earth takes 365 1/4 days to revolve around the Sun. However, for the sake of convenience, we consider a year as consisting of 365 days. The six hours ( 1/4th of 24hours) that are ignored make one day (24 hours) over a span of four years. This surplus day is added to the month of February. Thus, every fourth year, February has 29 days, and such a year (with 366 days) is known as a leap year.
