Have a look at the whos, whats and whens of leap year through time
The thing to know is that leap year exists, in large part, to keep the months in sync with annual events, including equinoxes and solstices, according to the Jet Propulsion Laboratory at the California Institute of Technology. Adding a leap day every four years would make the calendar longer by more than 44 minutes, according to the National Air & Space Museum. Later, on a calendar yet to come (we'll get to it), it was decreed that years divisible by 100 not follow the four-year leap day rule unless they are also divisible by 400, the JPL notes.
Source: yahoo.com
