The 2008 Leap Second
The end of 2008 will require one more second than did 2007, because of the need to have a ‘leap second‘. The international community has agreed that at 23:59:60 Greenwich Mean Time (GMT), there will be a one second pause in order to harmonize the atomic clocks to the rotation of the Earth. This will be the 24th leap second since 1972 and will be the first in three years. Due to the wobble of the Earth about its axis, the Earth now trails atomic clocks by approximately six-tenths of a second.
A leap second is a one-second adjustment that keeps broadcast standards for time of day close to mean solar time. Broadcast standards for civil time are based on Coordinated Universal Time (UTC), a time standard which is maintained using extremely precise atomic clocks. To keep the UTC broadcast standard close to mean solar time, UTC is occasionally corrected by an intercalary adjustment, or “leap”, of one second. Over long time periods, leap seconds must be added at an ever increasing rate (see ΔT). The timing of leap seconds is now determined by the International Earth Rotation and Reference Systems Service (IERS). Leap seconds were determined by the Bureau International de l’Heure (BIH) prior to January 1, 1988, when the IERS assumed that responsibility.
When a positive leap second is added at 23:59:60 UTC, it delays the start of the following UTC day (at 00:00:00 UTC) by one second, effectively slowing the UTC clock.
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