Every second will count in fight over future of time

British scientists and historians have united against an American proposal to change the way time is tied to the daily rotation of the Earth on its axis.

They believe that a plan to abolish the "leap" second ­ an extra second added to the midnight pips at new year ­ would in effect move the position of the Greenwich meridian eastwards.

The proposal from American time specialists is being debated today at a meeting of the International Telecommunication Union in Geneva and a decision is expected tomorrow.

It is believed that they want to scrap the leap second because of the technical problems it can cause when altering some atomic clocks.

However, Kristen Lippincott, deputy director of the National Maritime Museum in London, said that there were many disadvantages of abolishing the leap second. "If you get rid of the leap second you are destroying the notion of what time is," Dr Lippincott said.

"For the first time in history you will separate the timekeeping mechanism from the rotation of the Earth and the movement of the Sun and the stars. One practical effect is that the lines of longitude will slip gradually eastwards. I'm sure they are proposing this for the best interests but there is no reason for it," she said.

The rotation of the Earth has been used as the basis for timekeeping since the dawn of history, but the planet does not always complete a full rotation in exactly 24 hours, because it spins slightly slower every year.

To counteract this effect, and to keep time in synchrony with the Earth's daily cycle of night and day, timekeepers have sometimes added a "leap" second at the end of the pips, usually at new year but sometimes in June, or exceptionally in March or September.

Leap seconds are not added every year, and their appearance is judged necessary only after careful calculations about the speed at which the Earth's rotation has slowed down since the last leap second.

The International Earth Rotation and Reference Systems Service, an international body based at the Paris Observatory, has decided that an extra second will be added to the pips this new year.

Before the age of atomic clocks, leap seconds were not needed because clocks could be adjusted whenever it was thought necessary to do so.

But because atomic clocks are so accurate, leap seconds are needed to keep them tuned to the not-so-accurate clock of the Earth's daily rotation.

Jonathan Betts, curator of horology at the Royal Observatory, said that if leap seconds were abolished it would eventually mean that time would bear little relevance to whether it was day or night.

"For me it would be a problem if the Sun were to rise at 4pm or at a different time like noon or midnight," Dr Betts said. "I don't support the idea of the American delegation because I think all our human activities are linked to the rotation of the Earth first," he said.

A spokeswoman for the National Physical Laboratory, Britain's official timekeeper, said the proposal will be fought. "The UK is opposed to the proposal, and other countries have raised concerns over specific details," she said.

* The woman who presided as the voice of the speaking clock for 22 years has died. Pat Simmons, who was the voice of the service between 1963 and 1985, died in London, last week, aged 85. Originally from the East End, she was working at the London telephone exchange in 1963 when she won a competition to deliver the time and became a familiar voice before retiring in 1985.

A brief look at the history of time

* The "mean" in Greenwich Mean Time is derived from the need to average out the length of the solar day, which varies throughout the year

* John Flamstead, a former astronomer royal, calculated the rotation of the earth in the 17th century using the first accurate clocks

* Greenwich was chosen as the prime meridian in 1884 at a conference in Washington of 25 nations

* The first atomic clock was used to measure time in 1955

* Since 1972, Universal Time and International Atomic Time have been kept in synchrony by the addition of occasional "leap" seconds

* When a leap second is inserted it is done after the last second of either December or June, or exceptionally in March or September

* All leap seconds so far have been positive, meaning that they have been added to time. It is possible to take seconds away, should the earth's rotation begin to speed up

* There have been 22 leap seconds since 1972, the last one being in 1999.

* Traditional navigation, using the moon and stars, is one application that uses time to an accuracy of a few seconds