for National Geographic News
For those of you counting the seconds until 2006, add one.
The world's top timekeepers will insert an extra secondor leap secondjust before midnight in coordinated universal time (UTC) on New Year's Eve. (That's the same as 6:59:59 p.m. eastern time on December 31.) UTC is determined by atomic clocks and is five hours ahead of eastern time.
Earth's rotation is ever so slightly slowing down, but atomic clocks remain unwaveringly consistent. The extra second will allow Earth to stay in sync with the ultraprecise clocks, which mark time based on the vibration of atoms.
The planet's slowing is mostly due to the friction of tides raised by the gravitational pull of the sun and the moon. In fact, a day is now about two-thousandths of a second longer than it was a couple centuries ago, scientists say.
To keep today's atomic clocks synchronized with time as measured by Earth's rotation, timekeepers insert a leap second whenever the difference between the two clocks exceeds nine-tenths of a second.
The International Earth Rotation and Reference Systems, near Frankfurt, Germany, coordinates the additions of leap seconds.
This year's "extra" second will be the 23rd leap second added since 1972. In that year atomic timekeeping became the world standard. Before then, authorities relied on the movement of stars.
The most recent leap second was added seven years ago, in 1998.
"For the last several years Earth has behaved well," explained Geoff Chester, a spokesperson for the United States Naval Observatory in Washington, D.C. Together with the U.S. National Institute of Standards and Technology, the observatory keeps official time for the country.
But Earth is predicted to slow down "on a nearly exponential scale" in the decades to come as tidal friction increases, Chester says. And this is a conundrum that has sparked debate among the world's clock-watchers.
Abolish Leap Seconds?
As the Earth slows, the addition of leap seconds will be required more frequently to keep the Earth and atomic clocks in sync.
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