leap second

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leap second

n.
A second of time, as measured by an atomic clock, added to or omitted from official timekeeping systems periodically to compensate for small changes in the rotation of the earth and therefore the length of a solar day.

leap second

n
(Units) a second added to or removed from a scale for reckoning time on one particular occasion, to synchronize it with another scale

leap′ sec`ond


n.
an extra second intercalated into the world's timekeeping system about once a year, made necessary by the gradual slowing down of the earth's rotation.
[1970–75]
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.leap second - a second (as measured by an atomic clock) added to or subtracted from Greenwich Mean Time in order to compensate for slowing in the Earth's rotation
s, sec, second - 1/60 of a minute; the basic unit of time adopted under the Systeme International d'Unites
References in periodicals archive ?
Leap seconds are added periodically to adjust to irregularities in the earth s rotation in relation to Coordinated Universal Time (UTC), the current reference for measuring time, in order to remain close to mean solar time (UT1).
Since 1972, the keepers of the atomic clocks have sporadically added 25 leap seconds.
Geophysicist Chopo Ma, of the International Earth Rotation and Reference Systems Service, said: "More and more leap seconds will be called for but we can't say one will be needed every year.
Leap seconds are added to clocks worldwide to compensate for the slowing of the planet's rotation, affected due to friction caused by ocean tides.
Since the leap second procedure was introduced on January 1, 1972, a total of 25 leap seconds have been needed.
Throughout the 80s, leap seconds were added six times, but since 1999, only four leap seconds were added.
Leap seconds are designed to keep UTC aligned with astronomical time, which is based on the rotation of the Earth.
Although leap seconds caused by the need to compensate for the earth's rotation are extremely rare occurrences -- the last whole second adjustment would have happened in 1820 had atomic clocks and NTP servers existed -- there have in fact been 25 leap seconds for other reasons since the beginning of atomically-measured time in 1971.
The last leap seconds happened in 2008, 2005 and 1998.
Among specific topics are leap seconds in literature, time scales in astronomical and navigational almanacs, telescope systems at Lick Observatory and Keck Observatory, and automating retrieval of Earth orientation predictions.
Unlike leap years, which happen every four years-including 2012-and mean an extra day in February, leap seconds are added sporadically: The last one was in 2008 and the next will be on June 30.
As a leap year, and with two additional leap seconds added, it was the longest year ever.