Australia is about to sever a yet another historical link with Britain. It will abandon Greenwich Mean Time and adopt a new national standard next week, based on the atomic clock.
Rather than set their watches according to GMT, based on the movement of the sun over a brass mark at Greenwich on the Thames, Australians will adjust their chronometers according to the ultra-precise vibrations of a caesium 133 atom or, to give it a more formal name, Coordinated Universal Time (UTC).
”Really, GMT is just a little bit outmoded,” said Richard Britain of Australia’s National Measurement Institute. ”Scientific atomic clocks are the way to go in terms of accurate timekeeping. But nobody is going to get their day shortened or their life lengthened.”
New Zealand, Singapore, the United States and most of the European Union have already adopted UTC. When European space scientists land a probe one of the moons of Saturn, when Australian surveyors rendezvous with relief aircraft in the Antarctic, when Egyptian jumbo jet pilots land at Heathrow, they all use UTC.
British space scientists and Antarctic explorers also use UTC, which is ”maintained” by 40 time laboratories all over the world, using 260 atomic clocks. Some of these are at the National Physical Laboratory in Teddington, west London, and these keep British time accurate to about one second in three million years.
The most dramatic rupture, however, is with astronomy and with Australia’s own history. For Australians now, the second has been decoupled from the year, a measure of time marked by one complete revolution of the Earth around the Sun.
The decision to use Greenwich as the basis for the planet’s time grew out of the need to establish a reliable means of measuring longitude. One of the pioneers of accurate navigation was Captain James Cook, who tested the first modern chronometers and first mapped the Australian coast in 1769.
He started, of course, from the Greenwich meridian, already then home of astronomical research for more than a century. The rest of the world — with one exception — decided to adopt GMT as the global standard at a conference in Washington, in the US, in 1884.
”It was initially historical accident but in 1884, when we had the great conference on issues of longitude and so on, about 75% of the tonnage of the world’s shipping was using maps based on longitude zero at Greenwich,” said Robin Catchpole of the old Royal Greenwich Observatory.
”The bottom line is your map and your timekeeping have to refer to the same longitude. So it was really at that point that GMT was adopted for all the world. At the heart of it was our relationship with the French. The French were all in favour of adopting a universal time, but they abstained when it came to Greenwich. They never really adopted Greenwich, they adopted Paris time and a correction of 9 minutes and 11 seconds or something: the time difference between Greenwich and Paris.”
In fact, Britain too effectively adopted UTC. In 1925, the nation changed its timing reference point from noon at Greenwich to midnight, and adopted the term ”universal time” to avoid international confusion. GMT remained a conventional name for civil time in the UK. The second is now defined not as the a fraction of a day, and therefore an even smaller fraction of a year. It is 9 192 631 770 periods of radiation from a caesium atom in its ground state.
That means that every few years astronomers have to insert a ”leap second” to make the clock keep in step with the calendar. From next week, having abandoned British authority, Australians will be kept up to the second by scientists in France.
”The ultimate bemusement in all this is that it is the Bureau de l’Heure in Paris that governs when we enter leap seconds into coordinated universal time,” Dr Catchpole said. – Guardian Unlimited Â