Here's a timely reminder for all you would-be revelers out there: Be careful with your countdowns this New Year's Eve. There will be a little extra time to bask in the glow of a retreating 2016 — or curse its name, as the case may be.
Whatever your inclination, one thing is certain: Before the year is out, the world's foremost authority on time will be adding one more second to the clock.
In a bulletin released this summer, the International Earth Rotation and Reference Systems Service, or IERS, said it would be necessary to introduce a "leap second" at the end of December. Timekeepers use this added second much as leap years are used — to bring the world's atomic clocks in sync with the Earth's own distinctive rhythm, which in this case is determined by its rotation.
This leap second isn't the first. Since 1971, the world has added leap seconds with some regularity — typically every two to three years — and the latest leap second was added only last year, in June.
Why do these leap seconds keep cropping up? Peter Whibberley, a research scientist with the U.K.'s National Physical Laboratory, explains it this way:
"Atomic clocks are more than a million times better at keeping time than the rotation of the Earth, which fluctuates unpredictably. Leap seconds are needed to prevent civil time drifting away from Earth time. Although the drift is small — taking around a thousand years to accumulate a one-hour difference — if not corrected, it would eventually result in clocks showing midday before sunrise."
Recent research appears to back up Whibberley's assessment. According to a study published earlier this month in the Proceedings of the Royal Society A, Earth's rotation has slowed about 1.8 milliseconds per day — which means the solar day itself has lengthened, little by little. The researchers based this assessment on records dating back to 760 B.C., long before the implementation of the precise atomic clocks.