Tonight's 'Leap Second' Is Hot Tocking Point

By Dan Zak
Washington Post Staff Writer
Wednesday, December 31, 2008

This weary/manic/glorious/tragic/bizarre year will last one second longer than you think. As 2008 circles the drain, here comes the pithy news item about the "leap second." It's exactly what it sounds like. Tonight, timekeepers will slide an extra second into the world's clock. Tick tock tick tock TICK TOCK.

It will happen here, in Washington, a stroke before 7 p.m. The clock on the front lawn of the Naval Observatory will linger at 18:59:59 for two seconds instead of one. Then it will proceed, as if nothing happened, to 19:00:00.

Most computer clocks and cellphones will take note of this. You will not.

Perhaps you should. This minor quirk might soon vanish in a tussle of global proportions. The Brits want to keep the leap second. The United States and the world's other major powers want to dispose of it, thereby erasing the risk it poses to global telecommunications and navigation.

But if we get rid of the leap second, we effectively cut our ties to the sun.

"It would be a really bold cultural step to cut that link of maybe 5,000 years of history of measuring time," Royal Observatory timekeeping curator David Rooney says from London, where tonight, in the dying moments of 2008, BBC Radio will add a seventh pip (tone) to its traditional six-second countdown to the next hour, and where pennies will be removed from Big Ben's pendulum to slow it slightly in the final hour before midnight Greenwich Mean Time.

Tick tock tick tock TICK TOCK.

The leap second is a relic from the 1970s. Physicists whipped up this artificial hiccup to keep atomic clocks, which are reliably steady, aligned with the rotation of the Earth, which is slowing at a rate of two-thousandths of a second per day. So every now and then (1998, 2005, today) we allow the planet to catch up so that the sun remains highest at noon instead of, say, 11:59 a.m.

A leap second is kind of like a leap year, in that both are attempts at dicing cosmic progression into whole numbers: years made of days and days made of seconds. An extra day is notable. An extra second is nothing. Right?

It's one-86,400th of a day.

It's several billionths of a 75-year lifetime.

It's a blink.

It's also a wedge between new and old, micro and macro, between the severity of atomic precision and the romance of looking heavenward. Tick tock tick tock TICK TOCK.

Of course, it could be 700 years before atomic time and solar time diverge by as much as an hour. As author Douglas Adams once said, it will be someone else's problem.

"Today, most countries change one hour between summer and winter, and this creates no problem to people," says Elisa Felicitas Arias, a marker of time at the International Bureau of Weights and Measures in Paris, which sets the standard for the world's atomic clocks. "In the future -- many, many hundreds of years -- perhaps man will be faced with the decision of making some change, but at the moment I think we can live without the leap second, and we can live better without the leap second."

Living better. Because of a second.

But an extra second is nothing, right?

In a second, the Earth rotates a quarter-mile at the equator. In a billionth of a second, light travels one foot. Both of these matter when you turn on the GPS in your car. You know where you are because of a second.

Don't get too familiar with it. Eventually we must redefine the length of the second or deal with the hassle of more frequent leap seconds -- maybe occurring monthly a thousand years from now -- due to the constant deceleration of the Earth's rate of rotation, according to Dennis McCarthy, retired director of time at the Naval Observatory, which controls one-third of the world's atomic clocks.

"We're operating with a second that is not consistent with the way the Earth is rotating at this moment," McCarthy says. "We could change the length of a second, but then you'd be changing all sorts of things -- the meter is defined in terms of the length of a second -- and it would be a terrible thing to do. The easiest thing now is to begin to make plans for how to get along without the leap second. We owe it to future generations to start thinking of a better way."

Our way, right now, is delightfully tangled in our own quest to perceive and to measure. The immutable atomic standard is married, for better or worse, to the Earth's ever-changing rate of rotation. This paradox might soon be history if the International Telecommunication Union, based in Geneva, decides to abolish the leap second at its conference in 2011.

For now, though, we have a whole second more of 2008. It won't lengthen our lives but it will lengthen today, as we define a "day," and this year, as we define a "year," even though it holds us back one second, meaning we will die a smidgen earlier -- but not sooner -- than if no one had messed with the clocks. Tick tock tick tock TICK TOCK.