Leap second: Difference between revisions

Revision as of 23:07, 1 January 2004

Revision as of 16:32, 2 January 2004

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A '''leap second''' is a one-second adjustment to civil time in order to keep it close to the [[mean solar time]].

<table border="1" cellspacing="0" width="20%" cellpadding="2" align="right" style="margin-left:15px;">

<tr><td align=center>'''List of leap seconds'''

<tr><td>

# [[1 July]] [[1972]]

# [[1 January]] [[1973]]

# [[1 January]] [[1974]]

# [[1 January]] [[1975]]

# [[1 January]] [[1976]]

# [[1 January]] [[1977]]

# [[1 January]] [[1978]]

# [[1 January]] [[1979]]

# [[1 January]] [[1980]]

# [[1 July]] [[1981]]

# [[1 July]] [[1982]]

# [[1 July]] [[1983]]

# [[1 July]] [[1985]]

# [[1 January]] [[1988]]

# [[1 January]] [[1990]]

# [[1 January]] [[1991]]

# [[1 July]] [[1992]]

# [[1 July]] [[1993]]

# [[1 July]] [[1994]]

# [[1 January]] [[1996]]

# [[1 July]] [[1997]]

# [[1 January]] [[1999]]

</td></tr>

<tr><td></td></tr>

</table>

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.