Broken Secrets

Leap Years and Leap Seconds

January 1, 2010 at 12:01 am Chad Upton 1 comment

Happy New Year!

You probably know that leap years occur every four years. On leap years we add an extra day to keep our clocks and calendars in sync with Earth’s rotation.

On the other hand, most people don’t know about leap seconds. Leap seconds are used for the very same reason as leap years, to keep our clocks in sync with Earth’s rotation.

Because Earth’s rotation varies, leap seconds are added or subtracted up to twice per year when needed. Leap years add a day in February while leap seconds can be added at midnight on December 31st or June 30th when necessary.

An extra day on the calendar isn’t going to go unnoticed, but an extra second is difficult to sense. That’s why most of us don’t know about them. Accurate time keeping devices (atomic clocks) are updated appropriately and you may notice the update on connected devices like cell phones or GPS units, but generally it goes unnoticed by nearly all of us. The last two leap seconds were added on New Year’s Eve of 2005 and 2008. The next time a leap second will be added is not known.

Here’s a video that shows an extra second inserted between 59 and 00 on an atomic clock.

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Sources: WP – Leap Year, WP – Leap Second, TimeAndDate.com,

Entry filed under: Geek. Tags: atomic, clock, eve, leap, leap-second, new, second, secret, time, year, year's.