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.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

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]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
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
Based on WordNet 3.0, Farlex clipart collection. © 2003-2012 Princeton University, Farlex Inc.
References in periodicals archive ?
This is because the practice of leap seconds, like DST, is a contentions one.
The exact divergence between astronomical and atomic time is difficult to model or predict, but there are two general reasons why leap seconds are periodically needed.
Leap seconds have been added to our days since the 1970s and will continue to be added for years to come.
Since 1972, the keepers of the atomic clocks have sporadically added 25 leap seconds. The difference may not be noticeable to humans, but it confuses computers relying on old software and caused about five minutes of "instability" across the internet, according to web monitoring firm Dyn Inc.
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.
Since the leap second procedure was introduced on January 1, 1972, a total of 25 leap seconds have been needed.
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.
When they measure a sufficiently large lag in the Earth's movement, they then announce leap seconds, as they did earlier this year.
According to Stamatakos, the addition of leap seconds was really down to physics.
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.