Times they are a-changin'

The Times, they are a changing - literally.

After more than two decades of resistance, a Bill in the House of Lords this month may signal time out for a great British institution.

As astronomers await the fate of the Royal Greenwich Observatory, the Lords are deciding the future of an equally renowned phenomenon, Greenwich Mean Time (GMT), by which Brits have officially set their clocks since 1880.

GMTis under threat because the dawning of the 21st century poses a conundrum for scientists at the National Physical Laboratory, says research scientist John Chambers.

Asked how many seconds there are to go to the millennium, he explains there are tens of millions, give or take two or three in Europe - but not Britain.

This is down to the difference between GMT and coordinated universal time (UTC) as used by the rest of the world.

GMT relies on the earth's rotation and its orbit around the sun, which is not perfectly regular. Since it was established scientists have devised more accurate ways of counting seconds, such as using caesium-133 which provides a second beat one million times more stable than the earth's rotation, which is constantly slowing down.

This method is called international atomic time (TAI) and is used by scientists worldwide. But it is slightly faster than GMT. Since the establishment of TAI, a 30-second gap has developed between TAI and GMT.

To get around this, "leap" seconds are added to TAI to create UTC, a compromise between the discipline of atomic clocks and the less precise rotation of the earth.

The International Earth Rotation Service keeps track of the difference between UTC and GMT. When GMT gets too far behind UTC, another leap second is deemed necessary. Since January 1972, there have been 20 leap seconds. The next is at 1am on July 1.

UTC has been legally adopted in most of Europe, including Ireland. The BBC pips are based on UTC, as are most British clocks, but GMT is still Britain's legal time. This means that if you stand with your legs either side of the Irish borders, your feet could be legally up to a 0.9 of a second apart, effectively making time travel possible.

Now Lord Tanlaw, a part-time horologist, wants to bring Britain in line. He told the Lords: "The only hesitations I have met so far have been from those who might regret the passing of the historic term 'Greenwich' from the national time-scale."

He believes a term for world time zones incorporating the word Greenwich could be devised, such as Greenwich Meridian Time or Greenwich World Time.

The Bill, which passes to committee stage this week, could become law by the end of the year.

What's the time?

00 min 00 sec GMT (Greenwich Mean Time) Britain's official time since 1880, but no longer used, even for the BBC pips, except by amateur astronomers and in traditional navigation using the stars.

59 min 59.1 sec to 00 min00.9 sec UTC (Coordinated Universal Time) Est. 1972. Calculated by adding leap seconds to TAI. Got arecord 0.8 sec behind GMT in mid-1984. Official time in most of Europe including Ireland. Unofficial time in Britain.

00 min 30 sec, and counting TAI (International Atomic Time) Est. 1958. The most accurate method, used by scientists.The gap between it and GMT is widening all the time.