What Is A Leap Year?
The Earth takes 365.24219 days to orbit the sun. This means that, without leap years, the seasons would slowly change over time. Leap years help the calendar year stay in step with the astronomical year.
The first leap years were introduced by Julius Caesar over 2000 years ago. In the Julian calendar, a leap year fell every 4 years. This proved to be too many leap years, however, so the calendar was changed.
The Gregorian calendar (named after Pope Gregory XIII) has 365 days. A leap year containing an extra day occurs when the following rules are satisfied:
A year must be evenly divisible by 4 to be a leap year and if the year can be divided by 100 it is only a leap year if it can be divided by 400. So 2000 is a leap year, but 2100 is not.
The extra day is added to February making the 29th of February.