Happy Leap Day! every 4 years February adds an extra day to muck up the calendar and make confusing birthdays (looking at you Raspberry Pi)

Most people know the general idea: the earth doesn’t go around the sun exactly in 365 days. But for a lot of us the specifics get a little murky.

Check out the SciShow on YouTube for a full explanation and a surprising amount of caveats:

From NASA:

The length of a year is based on how long it takes a planet to revolve around the Sun. Earth takes about 365.2422 days to make one revolution around the Sun. That’s about six hours longer than the 365 days that we typically include in a calendar year. As a result, every four years we have about 24 extra hours that we add to the calendar at the end of February in the form of leap day. Without leap day, the dates of annual events, such as equinoxes and solstices, would slowly shift to later in the year, changing the dates of each season. After only a century without leap day, summer wouldn’t start until mid-July!

Read more