Editing Leap second (section)

==Procedure==
{| class="wikitable" style="float:right; margin-right: 0; margin-left: 1em; text-align: center;"
|+ Announced leap seconds to date<ref>{{cite web|title=TAI−UTC (1972-01-01 – 2024-06-28)|date=4 July 2023|access-date=4 July 2023|url=https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat}}</ref>
|-
! Year !! 30 Jun !! 31 Dec
|-
! 1972
|bgcolor="lime"| +1 ||bgcolor="lime"| +1
|-
! 1973
| 0 ||bgcolor="lime"| +1
|-
! 1974
| 0 ||bgcolor="lime"| +1
|-
! 1975
| 0 ||bgcolor="lime"| +1
|-
! 1976
| 0 ||bgcolor="lime"| +1
|-
! 1977
| 0 ||bgcolor="lime"| +1
|-
! 1978
| 0 ||bgcolor="lime"| +1
|-
! 1979
| 0 ||bgcolor="lime"| +1
|-
! 1980
| 0 || 0
|-
! 1981
|bgcolor="lime"| +1 || 0
|-
! 1982
|bgcolor="lime"| +1 || 0
|-
! 1983
|bgcolor="lime"| +1 || 0
|-
! 1984
| 0 || 0
|-
! 1985
|bgcolor="lime"| +1 || 0
|-
! 1986
| 0 || 0
|-
! 1987
| 0 ||bgcolor="lime"| +1
|-
! 1988
| 0 || 0
|-
! 1989
| 0 ||bgcolor="lime"| +1
|-
! 1990
| 0 ||bgcolor="lime"| +1
|-
! 1991
| 0 || 0
|-
! 1992
|bgcolor="lime"| +1 || 0
|-
! 1993
|bgcolor="lime"| +1 || 0
|-
! 1994
|bgcolor="lime"| +1 || 0
|-
! 1995
| 0 ||bgcolor="lime"| +1
|-
! 1996
| 0 || 0
|-
! 1997
|bgcolor="lime"| +1 || 0
|-
! 1998
| 0 ||bgcolor="lime"| +1
|-
! 1999
| 0 || 0
|-
! 2000
| 0 || 0
|-
! 2001
| 0 || 0
|-
! 2002
| 0 || 0
|-
! 2003
| 0 || 0
|-
! 2004
| 0 || 0
|-
! 2005
| 0 ||bgcolor="lime"| +1
|-
! 2006
| 0 || 0
|-
! 2007
| 0 || 0
|-
! 2008
| 0 ||bgcolor="lime"| +1
|-
! 2009
| 0 || 0
|-
! 2010
| 0 || 0
|-
! 2011
| 0 || 0
|-
! 2012
|bgcolor="lime"| +1 || 0
|-
! 2013
| 0 || 0
|-
! 2014
| 0 || 0
|-
! 2015
|bgcolor="lime"| +1 || 0
|-
! 2016
| 0 ||bgcolor="lime"| +1
|-
! 2017
| 0 || 0
|-
! 2018
| 0 || 0
|-
! 2019
| 0 || 0
|-
! 2020
| 0 || 0
|-
! 2021
| 0 || 0
|-
! 2022
| 0 || 0
|-
! 2023
| 0 || 0
|-
! 2024
| 0 || 0
|-
! 2025
| 0 ||
|-
! Year !! 30 Jun !! 31 Dec
|-
!rowspan="2"| Total
| 11 || 16
|-
|colspan="2"| 27
|-
!colspan="3"| Current TAI − UTC
|-
|colspan="3"| 37
|}

The scheduling of leap seconds was initially delegated to the [[Bureau International de l'Heure]] (BIH), but passed to the International Earth Rotation and Reference Systems Service (IERS) on 1 January 1988. IERS usually decides to apply a leap second whenever the difference between UTC and UT1 approaches 0.6&nbsp;s, in order to keep the difference between UTC and UT1 from exceeding 0.9&nbsp;s.

The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. {{As of|May 2023}}, all of them have been inserted at the end of either 30 June or 31 December. IERS publishes announcements every six months, whether leap seconds are to occur or not, in its "Bulletin C".<ref>See http://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat</ref>   Such announcements are typically published well in advance of each possible leap second date – usually in early January for 30 June and in early July for 31 December.<ref name="Bulletin C 36">{{cite web|last=Gambis|first=Daniel|title=Bulletin C 36|publisher=[[International Earth Rotation and Reference Systems Service|IERS EOP PC]], [[Observatoire de Paris]]|location=Paris|date=4 July 2008|url=http://tycho.usno.navy.mil/bulletinc2008.html|access-date=18 April 2010|url-status=dead|archive-url=https://web.archive.org/web/20091006221408/http://tycho.usno.navy.mil/bulletinc2008.html|archive-date=6 October 2009}}</ref><ref>{{Cite web|url=http://www.livescience.com/strangenews/081208-leap-second.html|title=2008 Will Be Just a Second Longer|author=Andrea Thompson|access-date=29 December 2008|publisher=Live Science|date=8 December 2008|url-status=live|archive-url=https://web.archive.org/web/20081212222023/http://www.livescience.com/strangenews/081208-leap-second.html|archive-date=12 December 2008}}</ref> Some [[time signal]] broadcasts give voice announcements of an impending leap second.
<!--
{| style="float:left;"
|{{Listen
|filename=Leap-second-announce.ogg
|title=Leap second announcement
|description=An example of a leap second announcement broadcast on [[WWV (radio station)|WWV]] in 2005.
}}
|} -->

Between 1972 and 2020, a leap second has been inserted about every 21 months, on average. However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six-year interval between 1 January 1999, and 31 December 2004, but there were nine leap seconds in the eight years 1972–1979.  Since the introduction of leap seconds, 1972 has been the longest year on record: 366 days, 364 of which were 86,400 seconds long and two of which were 86,401 seconds long, for a total of 31,622,402 seconds.

Unlike [[leap day]]s, which begin after 28 February, 23:59:59 local time,{{efn|Only the [[Gregorian calendar]]'s leap days begin after 28 February. The leap days of other calendars begin at different local times in their own years ([[Ethiopian calendar]], [[Iranian calendars]], [[Indian national calendar]], etc.).}} UTC leap seconds occur simultaneously worldwide; for example, the leap second on 31 December 2005, 23:59:60 UTC was 31 December  2005, 18:59:60 (6:59:60 p.m.) in [[U.S. Eastern Standard Time]] and 1 January 2006, 08:59:60 (a.m.) in [[Japan Standard Time]].

When it is mandated, a positive leap second is inserted between second 23:59:59 of a chosen UTC [[calendar date]] and second 00:00:00 of the following date. The definition of UTC states that the last day of December and June are preferred, with the last day of March or September as second preference, and the last day of any other month as third preference.<ref>{{cite web|url=https://www.itu.int/rec/R-REC-TF.460-6-200202-I/en|title=International Telecommunication Union Radiocommunications sector recommendation TF.460-6: Standard-frequency and time-signal emissions|access-date=9 February 2017|url-status=live|archive-url=https://web.archive.org/web/20161017185018/https://www.itu.int/rec/R-REC-TF.460-6-200202-I/en|archive-date=17 October 2016}}</ref> All leap seconds (as of 2019) have been scheduled for either 30 June or 31 December. The extra second is displayed on UTC clocks as 23:59:60. On clocks that display local time tied to UTC, the leap second may be inserted at the end of some other hour (or half-hour or quarter-hour), depending on the local time zone. A negative leap second would suppress second 23:59:59 of the last day of a chosen month so that second 23:59:58 of that date would be followed immediately by second 00:00:00 of the following date. Since the introduction of leap seconds, the mean solar day has outpaced atomic time only for very brief periods and has not triggered a negative leap second.

Recent changes to the Earth's rotation rate have made it more likely that a negative leap second will be required before the abolition of leap seconds in 2035.<ref>{{Cite web |last=Matsakis |first=Demetrios |date=September 21, 2022 |title=Will we have a negative leap second? |url=https://www.gps.gov/cgsic/meetings/2022/matsakis.pdf |access-date=3 June 2024 |website=gps.gov}}</ref><ref>{{Cite journal |last=Agnew |first=Duncan Carr |date=April 2024 |title=A global timekeeping problem postponed by global warming |url=https://www.nature.com/articles/s41586-024-07170-0 |journal=Nature |language=en |volume=628 |issue=8007 |pages=333–336 |doi=10.1038/s41586-024-07170-0 |pmid=38538793 |bibcode=2024Natur.628..333A |issn=1476-4687|url-access=subscription }}</ref>