‘Leap second’ to keep the world on time

LONDON • The world is about to get an extra long weekend, but don’t make big plans because it will only last an extra second.

A “leap second” will be added to atomic clocks as they undergo a rare adjustment to keep them in step with the Earth’s slowing rotation.

To achieve the adjustment, on Saturday night atomic clocks will read 23 hours, 59 minutes and 60 seconds before moving on to midnight Greenwich Mean Time.

Super-accurate atomic clocks are the ultimate reference point by which the world sets its wrist watches.

But their precise regularity — which is much more constant than the shifting movement of the Earth around the Sun that marks out our days and nights — brings problems of its own.

If no adjustments were made, the clocks would move further ahead and after many years the Sun would set at midday. Leap seconds perform a similar function to the extra day in each leap year that keeps the calendar in sync with the seasons.

In recent years a leap second has been added every few years, slightly more infrequently than in the 1970s despite the long-term slowdown in the Earth’s rotation caused by tides, earthquakes and a host of other natural phenomena.

Adjustments to atomic clocks are more than a technical curiosity. The highly accurate devices are used to set Co-ordinated Universal Time, which governs time standards on the world wide web, satellite navigation, banking computer networks and international air traffic systems.

Opponents of the leap second want a simpler system that avoids the costs and margin for error. Supporters argue it needs to stay to preserve the precision of systems in areas like navigation.