An extra second won't help revellers recovering from New Year's Eve, but it will help restore balance to the Earth's timescale.
At 7:59:59am on January 1, 2006, Hong Kong time, a leap second will be added to the co-ordinated universal time (UTC). The Hong Kong standard time, which is exactly eight hours ahead of UTC, will accordingly be delayed by one second. The whole process will be completed in two seconds at 8am Hong Kong time.
UTC is a stable and uniform timescale based on atomic clocks. This is the international time scale for virtually all nations for civilian purposes. It matches the astronomical timescale, which is based on the Earth's rotation.
Geological rotation, however, is uneven because it has been slowing - hence the need to adjust UTC periodically to make sure the timescales are synchronised.
'The purpose of introducing a leap second is to reconcile the two timescales so that their difference is kept at less than 0.9 of a second,' Observatory scientific officer Chan Ying-wa said.
He said that as the Earth was not a solid sphere, the atmosphere and oceans created friction, slowing its rotation.
