Just like in a leap year when an extra day is added to the end of February, a leap second’s purpose is to readjust atomic clocks to the gradual decrease in rotation of the Earth. This year, on December 31, 2008 at 6:59PM EST, the official clocks of the world will add an extra second to accommodate the time, thus making the clock display 6:59:60PM EST (the clock will show 23h 59m 60s in Coordinated Universal Time at this time).

Well, now you know!