Leap second to be added on January 1, 2017

22 December 2016

The Hong Kong Observatory today (December 22) reminded the public that a leap second will be introduced to Coordinated Universal Time (UTC) between 7.59.59am and 8.00.00am (Hong Kong Time) on January 1, 2017. Hong Kong standard time, exactly eight hours ahead of UTC, will be delayed by one second accordingly.

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

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

The astronomical time scale based on the Earth's rotation is another common time scale. As it is relatively uneven and slightly slower, 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.

More information on leap seconds can be found at:

www.hko.gov.hk/gts/time/basicterms-leapsecond.htm