A solar year–is about 365.2422 days long. Using a calendar with 365 days every year would result in a loss of almost six hours per year. After 100 years, this calendar would be more than 24 days ahead of the season. It is desirable to align the calendar with the seasons and to make any difference as insignificant as possible. By adding a leap year approximately every fourth year, the calendar will align with the seasons much more accurately. The last time a leap day was on a Friday was 1980. See here for more info.
Why am I telling you this? Because it’s HIS birthday of course! As he only gets a ‘real’ birthday once every 4 years and has to celebrate on a day other than his birthday so much, we really ring in an official birthday with style!