Why the U.S. Wants To End the Link Between Time and Sun

Astronomers Say Wait a Sec, Sundials Would Be Passé; Mean Blow to Greenwich

  • | Staff Reporter of

What time is it when the clock strikes half past 62?

Time to change the way we measure time, according to a U.S. government proposal that businesses favor, astronomers abominate and Britain sees as a threat to its venerable standard, Greenwich Mean Time.

Word of the U.S. proposal, made secretly to a United Nations body, began leaking to scientists earlier this month. The plan would simplify the world's timekeeping by making each day last exactly 24 hours. Right now, that's not always the case.

Because the moon's gravity has been slowing down the Earth, it takes slightly longer than 24 hours for the world to rotate completely on its axis. The difference is tiny, but every few years a group that helps regulate global timekeeping, the International Earth Rotation and Reference Systems Service, tells governments, telecom companies, satellite operators and others to add in an extra second to all clocks to keep them in sync. The adjustment is made on New Year's Eve or the last day of June.

[Earth's rotation]

But adding these ad hoc "leap seconds" -- the last one was tacked on in 1998 -- can be a big hassle for computers operating with software programs that never allowed for a 61-second minute, leading to glitches when the extra second passes. "It's a huge deal," said John Yuzdepski, an executive at Symmetricom Inc., of San Jose, Calif., which makes ultraprecise clocks for telecommunications, space and military use.

On Jan. 1, 1996, the addition of a leap second made computers at Associated Press Radio crash and start broadcasting the wrong taped programs. In 1997, the Russian global positioning system, known as Glonass, was broken for 20 hours after a transmission to the country's satellites to add a leap second went awry. And in 2003, a leap-second bug made GPS receivers from Motorola Inc. briefly show customers the time as half past 62 o'clock.

"A lot of people encounter problems with their software going over a leap second," said Dennis D. McCarthy, who drafted the U.S. leap-second proposal while serving as the Navy's "Director of Time." Because of these problems, the U.S. government last year quietly proposed abolishing leap seconds to the International Telecommunications Union, the U.N. body that tells the Earth Rotation Service how to keep time.

"Safety of life is an issue," said William Klepczynski, a senior analyst at the State Department in favor of the U.S. proposal, who asserts that programmers who ignore the need to add leap seconds present a "risk to air travel in the future" because a glitch might shut down traffic-control systems.

Eliminating leap seconds will make sextants and sundials slowly become inaccurate, but supporters say that's OK now that the satellite-supported GPS can give exact longitude and latitude bearings to anyone with a receiver. Sailors "don't navigate with the stars any longer," said Dr. McCarthy.

But the U.S. proposal, which an ITU committee will consider in November, has upset some of the most powerful people in timekeeping -- including the Earth Rotation Service's leap-second chief, Daniel Gambis, of the Paris Observatory. "As an astronomer, I think time should follow the Earth," Dr. Gambis said in an interview. He calls the American effort a "coup de force," or power play, and an "intrusion on the scientific dialogue." A 2002 survey of his subscribers found that 90% were content to keep leap seconds, he said.

On July 5, Dr. Gambis sent an email out to those timekeepers, tipping them off about the U.S. proposal, which would end leap seconds starting in 2007. Dr. Gambis urged email recipients to contact their countries' ITU delegations.

This has set off a wave of passionate opposition from astronomers, who argue that removing the link between time and the sun would require making changes to telescopes, changes that would cost between $10,000 and $500,000 per facility. That's because a fancy telescope uses the exact time and the Earth's position for aiming purposes when astronomers tell it to point at a specific star.

"We should not so blithely discard the ties between our clocks and the rotation of the Earth," wrote Rob Seaman, a programmer at the National Optical Astronomy Observatories in Tucson, Ariz. Jean Meeus, an influential Belgian astronomer, called the U.S. proposal "a disaster for classical astronomy" and a "dirty trick."

The U.S. effort to abolish leap seconds is also firmly opposed by Britain, which would further lose status as the center of time. From 1884 to 1961, the world set its official clocks to Greenwich Mean Time, based on the actual rise and set of the stars as seen from the Royal Observatory in Greenwich, just outside London.

When countries moved to the current Coordinated Universal Time, which uses extremely precise atomic clocks, they agreed to insert leap seconds in order to keep the official time within one second of the old Greenwich time. Even though Big Ben -- and the time broadcast by the British Broadcasting Corp. -- now follow Coordinated Universal Time, Parliament has declined to change the country's official standard away from Greenwich time, which remains a point of English pride.

Abandoning leap seconds would force the issue and make the world slowly drift away from Greenwich time. So Britain's science minister, Lord Sainsbury of Turville, decided in April, during Tony Blair's re-election campaign, to oppose the U.S. proposal. "It could have been used to attack the government," said Peter Whibberley, a scientist who represents Britain to the ITU. "People regard GMT with some sensitivity," he said. "It gets tied up with the general anti-Europe feeling."

Ending leap seconds would make the sun start rising later and later by the clock -- a few seconds later each decade. To compensate, the U.S. has proposed adding in a "leap hour" every 500 to 600 years, which also accounts for the fact that the Earth's rotation is expected to slow down even further. That would be no more disruptive than the annual switch to daylight-saving time, said Ronald Beard of the Naval Research Laboratory, who chairs the ITU's special committee on leap seconds and favors their abolishment. "It's not like someone's going to be going to school at four in the afternoon or something," he said.

For now, U.S. officials still regard their proposal as secret, despite Dr. Gambis's email and the public comments. The head of America's delegation to the ITU's timing committee, D. Wayne Hanson of the National Institute of Standards and Technology, declined to take calls on the matter. Through a spokeswoman, he said that the U.S. proposal is a private matter internal to the ITU and not for public discussion.

That secrecy outrages the astronomers, who complain that there is no reason to make the change by 2007, especially when many telescopes will have to be upgraded. The State Department's Dr. Klepczynski argues that it's better to eliminate possible computer bugs before an accident happens. "Some people are afraid to act on prevention," he said.

The astronomers are not convinced. "If your navigation system causes two planes to crash because of a one-second error, you have worse problems than leap seconds," said Steve Allen, a University of California astronomer who maintains a Web site about leap seconds.

Deep down, though, the opposition is more about philosophy than cost. Should the convenience of lazy computer programmers triumph over the rising of the sun? To the government, which worries about safety more than astronomy, the answer is yes. In Mr. Allen's view, absolutely not. "Time has basically always really meant what you measure when you put a stick in the ground and look at its shadow," he said.

Write to Keith J. Winstein at keith.winstein@wsj.com

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