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Boffins quarrel over ridding world of leap seconds

What should set the time - atomic watches or the sunrise?

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The measurement and regulation of time could start to change this week if an ITU meeting in Geneva, Switzerland, gives the nod.

International Telecommunication Union members are discussing whether Co-ordinated Universal Time (UTC) should be set using a system that does not factor in the Earth's imperfect spin – which necessitates the insertion of a leap second every so often so clocks can stay precisely synchronised with the world's uneven rotation.

UTC is based on the planet's revolutions and International Atomic Time (TAI), the latter of which is set by a network of 300 atomic clocks that don't lose track of time. The leap second was introduced in 1971 to keep the gap between the atomic clocks and the time according to the Earth's rotation at less than 0.9 seconds.

UTC was preferred over TAI as the standard time reference because it's more useful for mariners; it was believed a system that factored in the Earth's spin was needed for accurate navigation on the high seas.

However, some now say UTC will become unworkable because the planet's rotation is slowing down - meaning more leap seconds are needed. Other factors that can also affect the rotation include melting polar ice caps.

Steve Allen, of the Lick Observatory in Santa Cruz, California, has calculated UTC will require one leap second inserted per month by the year 3752. Back in the 21st century, leap seconds are inserted in December or June - the last leap second was added on 31 December, 2008, and the next is scheduled for 30 June this year.

Adding leap seconds poses technical challenges and potential dangers for systems that rely on time measurements, according to proponents of change: chiefly, servers, air traffic control, GPS and space missions. Software that relies on timestamps for transactions or for actions such as geo-location has to be updated to compensate for each change.

For instance, space agencies won't schedule lift-offs for days when leap seconds are added, and servers at Google apparently failed to handle a 2005 update. Google now runs the clocks on its computers slowly for a short period before an adjustment is due, ensuring the insertion of a leap second is a gradual process rather than an instantaneous one.

There are opponents to the potential change. Among them are ITU reps from Britain. Markus Kuhn, a computer scientist at the University of Cambridge and ITU member, has argued that there's a lack of credible evidence for serious problems caused by leap seconds, adding that computers can easily cope with leap seconds.

"We must not give up the >5,000 years old human practice of defining time through Earth's rotation because of unfounded worries of some air traffic control engineers," he wrote.

If the ITU agrees to remove leap seconds at this week's meeting it will be put to a vote at its next confab in September. ®

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