Leap years

A leap year is a year that has 366 days instead of 365. This extra day is 29th of February. We can have a leap year every four years.

Leap years exist because the Earth doesn't take exactly 365 days to go around the sun. It takes a bit less than 355 days and 6 hours. Our calendar ignores these 6 hours and "accumulates" them so every four years we have accumulated a day and we add this day to February.

This kind of years has existed since the year 46BC. It began with the julian calendar created by Julius Caesar. This calendar created an extra day every four years.

Actually there are some interesting facts about leap years. For example 2000 or 1800 are leap years, but 1900 or 1700 are not leap years because century leap years must be divisible by 400.