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Leap second to be added on July 1, 2012

19 April 2012

A leap second will be introduced to the Coordinated Universal Time (UTC) between 7:59:59 a.m. and 8:00:00 a.m. (Hong Kong Time) on 1 July 2012. The Hong Kong standard time, exactly eight hours ahead of UTC, will be delayed by one second accordingly.

UTC is a stable and even time scale based on the frequency of atomic oscillations in atomic clocks. This is the current international time scale for civil use.

The astronomical time scale based on the Earth's rotation is another common time scale. As a result of atmospheric circulation and other geophysical events on Earth, the rate of the Earth's rotation is uneven and slowing down. At present, one second based on the astronomical time scale is slightly longer than that based on the standard atomic time scale. It is therefore necessary to add a leap second from time to time to reconcile the two time scales so that the difference between them is kept below 0.9 of a second.

Leap seconds have been introduced 25 times since the adoption of UTC in 1972. The last adjustment was made on 1 January 2009.

The Observatory advises stakeholders and operators in information technology, telecommunication, transport sectors etc. to review whether systems under their management could handle leap seconds properly, and if necessary, to consider testing and adjusting their systems to ensure normal operations during and after the introduction of the leap second.

More information on leap seconds can be found at: .