for National Geographic News
Those anxious to bid adieu to 2008 must endure the tiniest of delays: This year will be one second longer.
A "leap second" will be tacked on to the world's timepieces as the year expires at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC).
The chronological change spotlights some of the quirks of an increasingly critical task—keeping the world's clocks perfectly synced.
(Related: "Leap Year: How the World Makes Up for Lost Time" [February 28, 2008].)
The international time standard UTC is an atomic time scale derived from a variation of the metallic element cesium's atom.
This atomic clock "ticks" with microwave light about nine billion times each second, allowing people to slice and dice time with extreme precision.
UTC is kept by the France-based International Bureau of Weights and Measures, which gathers contributions from labs in some 50 nations and computes an internationally agreed-upon average.
Zero hours UTC occurs at midnight in Greenwich, England, which lies at zero degrees longitude. (UTC was once referred to as Greenwich Meridian Time.)
The rest of the globe is divided into 24 15-degree longitude bands, each representing an hour's difference as one moves through time zones around the planet.
Why a Leap Second?
This year's leap second—the 24th to be added to UTC since 1972—exists because time was traditionally based on a full rotation of the Earth and was related to heavenly bodies, which defined the length of the day.
This rotational time, called UT1, divides the day into 86,400 seconds.
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