Leap seconds are added to adjust for changes in the rate of Earth’s spin (Image: Stock Xchng)

Those eager to see 2008 come to a close will have to wait a second longer. A single leap second will be added at the end of the year to accommodate a subtle slow-down in the Earth’s rotation.

The decision, made earlier this year by the International Earth Rotation and Reference Systems Service, will adjust coordinated universal time (UTC), which is used to calibrate national and regional clocks around the world.

The leap second will be added on 31 December 2008 at 23 hours, 59 minutes and 59 seconds UTC.


UTC time is counted by atomic clocks, but it is adjusted occasionally to accommodate changes in the length of the Earth’s day.

Tugs from the Sun and Moon are gradually slowing the Earth’s spin and causing its days to get longer. But this deceleration occurs unevenly.

The speed of the Earth’s rotation sometimes gets a subtle boost due to a complex coupling between the Earth’s mantle and core, which are thought to spin at somewhat different rates.

To accommodate the unevenness of this slow-down, leap seconds can be added twice a year – at the end of June and at the end of the December.

This leap second will be the 24th added to the world’s clocks since 1972, and the first one added since the end of 2005. No leap seconds were added between the end of 1998 and the end of 2005 due to a slight, temporary acceleration in the Earth’s rotation.