Leap second: Difference between revisions

Revision as of 14:39, 22 March 2004

Revision as of 18:57, 5 April 2004

Line 29:

|}

Civil clock time is based on [[UTC|"Coordinated Universal Time" (UTC)]], which is maintained by extremely precise [[atomic clock]]s. In contrast, the rotation of the Earth, measured by the [[UT1]] timescale, is irregular; the solar day is gradually but unevenly becoming longer, mainly due to the [[tidal acceleration]] of the [[Luna|Moon]]. In order to keep solar time close to civil time, UTC is corrected by a leap of 1 second.

The instruction to insert a leap second will be given whenever the difference between UTC and UT1 is expected to exceed 0.9 s. After UTC 23:59:59, an additional second at 23:59:60 is counted, before the clock jumps to 00:00:00 of the next day. Negative leap seconds are also possible if the Earth's rotation becomes slightly faster, but this has never happened. In that case, 23:59:58 would be followed by 00:00:00.