Hang on a second: Hong Kong clock adjustment to keep city's time in line with rest of world

An extra second will be added to Hong Kong standard time on the morning of July 1 to keep it in line with the world’s official atomic clocks.

The so-called leap second is added to coordinated universal time (UTC), the international standard time for civil use, every few years. The last adjustment was made on July 1, 2012.

The extra second will be added to the midnight of June 30 (UTC). That will be 8am on July 1 in Hong Kong.

The Hong Kong Observatory said the reason for adding a second is that the earth’s rotation is slowing due to atmospheric circulation and geographical events such as earthquakes.

As a result, one second based on the astronomical timescale is slightly longer than that based on the standard atomic timescale.

“It is therefore necessary to add a leap second from time to time to reconcile the two timescales so that the difference between them is kept below 0.9 of a second,” an Observatory spokesman said.