Leap Second
http://www.npl.co.uk/time/leap_second.html
I know this is kinda old news, but it's interesting anyhow. About every 18 months, there will be a leap second. In the case of a leap second, the last minute of the last day of either june or december will have 61 seconds. The last minute of december 31st this year, for one, will be 61 seconds long.

Don't forget to set your clocks accordingly. You just dont wanna be late for work as a result.