This year a day and a second longer
The International Earth Rotation and Reference Systems Service has decided that a positive leap second will be added to Coordinated Universal Time (UTC) at the end of June 2012.
While a leap second can be added and taken from any month, it has only occurred at the end of December and June. The most recent leap was added on December 31, 2008.
This will affect all time scales based on UTC, however the change to GPS will be automatic within the navigation message transmitted by satellites.
A leap second is necessary because of the Earth's unpredictable rotation.
UTC is based on atomic clocks, but has been kept more or less synchronised with mean solar time by way of leap seconds.
A revision of Standard-frequency and time-signal emissions will be voted by the International Telecommunication Union Radiocommunication Assembly meeting, immediately before the World Radiocommunication Conference 2012 (WRC-12), in Geneva this month.
A revision of Recommendation ITU-R TF.460-6 "Standard-frequency and time-signal emissions" will be voted on, and if approved, eliminates them by 2018. Highly accurate atomic clocks will be our sole method of time. Leap seconds introduced in 1972 would end.
Meantime with this being a so-called leap year, February will have a total of 29 days instead of the usual 28, to make up for our rotation around the Sun.
Jim Linton VK3PC
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