2008 is a leap year, so Friday will be February 29th, a date that rolls around just once every four years. If that’s your birthday, that makes you, what, eight? Ten?

Confused? Well, here’s the short explanation. Our year is measured by how long it takes the Earth to go around the Sun. It doesn’t take 365 days but 365 1/4. Actually… 365 days, 5 hours, 48 minutes, and 46 seconds. So, every four years we effectively lose a day. To prevent drift in our calendar we adjust the four year period to be 1,461 instead of 1,460 days. You can read more on The “Straight Dope” website.

Anyway, here are three smart things you should know about leap years in order to impress your friends and maybe win a few beers, compliments of Wired Magazine:

1) A leap year is any year evenly divisible by four — except for century years, which have to be divisible by 400. It’s not a perfect system: The Gregorian year is 27 seconds longer than the astronomical year. By 12008, we’ll be three days off.

2) October 5-14, 1582, never happened in Catholic lands. Brits (and their American subjects) born September 3 to 13 had no birthday in 1752. Those days were dropped when the Western world switched from the Julian to the Gregorian calendar.

3) International Atomic Time — kept by ultraprecise clocks — is gradually out-pacing astronomical time, which is determined by our planet’s rotation. (Earth’s spin is slowing — what a drag.) So in 1972, the International Earth Rotation and Reference Systems Service began adding occasional leap seconds. They’ve done it 23 times, most recently adding an extra “one-Mississippi” on December 31, 2005.