http://www.abc.net.au/news/2012-07-01/extra-second-added-to-atomic-clocks/4103204
An extra second has been added to the world’s atomic clocks in a rare adjustment to keep them in step with the slowing rotation of the Earth.
The so-called leap second was added to electronic clocks at midnight universal time on Saturday.
At that time, atomic clocks read 23 hours, 59 minutes and 60 seconds before they moved on to 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 which keeps the calendar in sync with the seasons.
The last so-called leap seconds happened in 2008, 2005 and 1998.
Adjustments to atomic clocks are more than a technical curiosity.
A collection of the highly-accurate devices are used to set Coordinated Universal Time which governs time standards on the world wide web, satellite navigation, banking computer networks and international air traffic systems.
There have been calls to abandon leap seconds but a meeting of the International Telecommunications Union, the UN agency responsible for international communications standards, failed to reach a consensus in January.
Opponents of the leap second want a simpler system that avoids the costs and margin for error in making manual changes to thousands of computer networks.
Supporters argue it needs to stay to preserve the precision of systems in areas like navigation.
A decision is not urgent. Some estimate that if the current arrangement stays, the world may eventually have to start adding two leap seconds a year. But that is not expected to happen for another hundred years or so.
not very often we gain time..