Leap Second

December 31st will be a long day this year. One second longer, to be exact. The earth’s trip around the sun doesn’t exactly correspond to our calendar, as it takes 365.2422 days. That’s why we add a day for leap year every four years, but it still doesn’t come out even, so every once in a while, another second is added to the last day of the year.

The International Earth Rotation and Reference Systems Service is the organization that monitors the difference in the two timescales and calls for leap seconds to be inserted or removed when necessary. Since 1972, leap seconds have been added at intervals varying from six months to seven years — the most recent was inserted on Dec. 31, 2005.

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(image credit: Flickr user slack12)