Got a second? Good. The Earth needs it. The planet’s spin has been slowing in the past seven years and it needs an extra second on New Year’s Eve. That will reconcile the relentless tick of atomic clocks with planet’s more leisurely rotation. Earth’s spin has been slowing, said Tom O’Brian, chief of the Time and Frequency Division at the National Institute of Standards and Technology in Boulder, Colo. To recognize the slightly longer days, international timekeepers will introduce a “leap second” at midnight in Greenwich, England, on Saturday, for the first time in seven years. It will be the 22nd leap second added since the current timekeeping system was adopted in 1972, and it may be the last, if leap second opponents have their way. “For most of human history, time was based on the rotation of the Earth,” O’Brian said. Then, about 50 years ago, researchers invented ultra-precise atomic clocks, which showed that the Earth’s rotation is anything but constant. The moon’s gravitational pull, for example, creates friction with the Earth, slowing the planet’s spin ever-so-slightly every year, O’Brian said. The internal churnings of the planet’s molten core can also affect the spin, increasing or decreasing day length. Even weather has an impact, O’Brian said. During winter in the Northern Hemisphere, water piles up as snow and ice in high-latitude mountains, shifting mass away from the center of the planet. “Like a (spinning) ice skater moving her arms out from the center slows down, that slows us down,” he said. Most astronomers like leap seconds because their methods of locating distant objects – and even situating the Earth in a three-dimensional map of space – rely on the old time system. Noon is when the sun is most directly overhead. A day is the length of time it takes for the planet to spin exactly 360 degrees. Others point out that the world is increasingly reliant on the atomic clocks in Global Positioning Systems, communications satellites and other high-tech devices. Adding leap seconds to those systems “can make them very vulnerable,” said Geoff Chester, spokesman for the Naval Observatory in Washington, D.C., which keeps time for the Department of Defense. “In a way it makes the Y2K problem look like a walk in the park,” he said. “Computers have been programmed to believe the fund units of time, that a minute is always 60 seconds.” Traditionalists say computer problems have been fixed, and very few systems remain vulnerable to glitches. Scientists around the world will be watching how satellites handle Saturday’s 61-second minute. Next year, the union may decide between sticking with the time system or ditching the leap second in favor of, say, a leap hour, which would happen every 500 years or so. “I guess I’m a traditionalist,” said NASA researcher Richard Gross, at the Jet Propulsion Laboratory in Pasadena. “But I don’t see a need to do away with the leap second.”160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set!