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Hands off our leap seconds, say astronomers

Big Ben

Should our clocks keep changing to keep in step with how fast the Earth spins? Some think not (Image: iStockphoto)

An international storm is brewing over whether to abolish the leap second, one of which is due to be added to clocks at the end of the year.

Astronomers are alarmed at the proposal and say their clocks must be exactly synchronised with the Earth's rotation. But others say getting rid of leap seconds will make the world a safer place.

The UK's Royal Astronomical Society is the latest to weigh into the debate, due to be formally aired at a November meeting of the International Telecommunications Union (ITU) in Geneva, Switzerland, which co-ordinates global telecommunication networks and services.

Astronomers says getting rid of leap seconds would make it hard for them to train their telescopes on distant stars and could cause problems for navigation and surveying.

But some argue having to insert the occasional leap second into clocks can cause computer glitches and havoc in communications.

The unit of time we know as a 'second' is defined in terms of the length of the day as it was in the year 1900.

But as the Earth's spin is slowing down, leap seconds are inserted into standard time, or UTC (Co-ordinated Universal Time), around once ever 18 months.

"The proposed change would cause UTC to drift with respect to solar time," the UK astronomy society says.

The society wants the proposal to abolish leap seconds shelved and is calling on the ITU to promote broader debate.

A setting Sun at midday?

Australian astronomer, Dr John Reynolds at the Parkes Observatory, says if solar time and ordinary time are allowed to slip we could end up with some pretty strange phenomena.

"Noon will eventually coincide with sunrise if we leave it long enough," he says, although this would take thousands of years.

But the Wall Street Journal reports that US experts, including the navy's 'director of time', Dennis D McCarthy who drafted the ITU proposal, wants to get rid of leap seconds because of problems with software.

The newspaper reports that the addition of a leap second in January 1996 caused computers at Associated Press Radio to crash and start broadcasting the wrong programs.

And that in 1997 adjusting to a leap second caused a Russian global positioning system Glonass to break down for 20 hours.

And it reports concerns that having to adjust to leap seconds could even cause a glitch that shuts down traffic-control systems and present a risk to future air travel.

The kludge factor

Australian space researcher Dr Duncan Steel, author of a book on the history of time-keeping, says leap seconds are a "techno-fix that are not really needed".

"Any fix like this, what computer scientists call a kludge, almost inevitably leads to problems, often unforeseen," he says.

"I can see why the ITU might think this is just an unnecessary complication. I think they've got a valid argument."

He says one of the problems of keeping our system of leap seconds is that because the Earth is continuing to slow down we will need them more frequently in the future.

Redefining the second?

Steel says an alternative to leap seconds could be to redefine a 'second' by basing it on the length of the day in 2000 rather than 1900.

But because seconds are the fundamental unit on which other units such as length are based, this would lead to worse technical problems than exist with leap seconds.

"That would worse thing to do," he says. "The metre would then get redefined."

Tags: government-and-politics, astronomy-space, computers-and-technology, information-technology