Those of you who get paid every other Friday might get three paychecks this month. It's rare for that to happen in February, which normally has only 28 days and struggles to create five Fridays. It happened last in 1908 and won't come again until 2036.
The reason, of course, is that Friday, Feb. 29 is the day this year, like every fourth year, that we leap to fix the calendar. Why do we need to? Because Earth's trip around the sun is about 365.2422 days long, not the 365 that we've deemed to be a year. Every four years, we add 0.2422 x 4.
Did you know that every few years, a "leap second" is added to make up for the slowing down of the Earth's rotation? That last happened in 2005.