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Seconds out: bid to alter the world's time


Time will never be the same again if the international organisation responsible for setting the world's clocks votes later this month in favour of a controversial plan to abolish the "leap" second – the extra second added to the time signal once every few years.

Click here to see the 'Keeping time - The role of leap seconds' graphic

Experts from around the world are scheduled to vote on eradicating the leap second at a meeting in Geneva next week of the International Telecommunications Union, the UN agency responsible for timekeeping standards.

Debate about the merits and drawbacks of the leap second has raged for many years, but observers believe this ballot could mark its final demise, although not before another one is added to the midnight signal on 30 June 2012.

The leap second was first introduced in 1972 and since then has been used on 24 occasions to keep astronomical time – which is based on the rotation of the Earth – in synchrony with international atomic time, based on the highly regular vibrations of a caesium atom.

Leap seconds were introduced because the rotation of the Earth is slowing down very slightly, by about two thousandths of a second per day, which means that without leap seconds atomic time would go an extra second ahead of astronomical time once every 500 days or so.

A leap second is added when necessary to atomic time to decrease the difference between astronomical time and coordinated universal time (UTC).

And to complicate matters the slowing down of the Earth's rotation is not constant, which means it has to be monitored constantly. Many organisations, including Britain's Royal Observatory, have been happy with the leap-second arrangement to keep astronomical time in harmony with atomic time.

But other organisations, such as the International Bureau of Weights and Measures in Paris, are not, and are now pressing for its demise."The proposal has been put forward and a decision is likely to be made one way or the other. There is little support for it here in Britain but considerable support elsewhere and there's a very real possibility that it may go through," said Jonathan Betts, senior curator of horology at the Royal Observatory.

"We think this would be a shame. We feel that it's important not to lose the link between the measurement of time and the Sun, which after all has been fundamental to the human timescale," Dr Betts said."It would disconnect us from nature, which is not what people want."

Those in favour of abolishing the leap second argue that many critical systems, such as the GPS instruments used in aircraft navigation or computer-trading systems used in international finance, depend on highly accurate timekeeping, which might fail if people forget to update them.

"The argument in favour of the change says that its dangerous setting these systems manually – they are worried about introducing errors. But we've been doing such adjustments for decades without any problems," Dr Betts said.