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Leap second to be added on 1 July
(25 June 2012)

A leap second will be introduced to the Coordinated Universal Time (UTC) between 7:59:59am and 8:00:00am (Hong Kong time) on 1 July 2012.

Scientific Officer of the Hong Kong Observatory, Mr Woo Wang-chun, said, "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 to 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.

More information on leap seconds can be found at and
Last revision date: <31 Dec 2012>