Photo by <a href="">Natmandu</a> (<a href="">CC</a>).
Photo by Natmandu (CC).

Policy Innovations Digital Magazine (2006-2016): Briefings: Time Out

Dec 18, 2008

Five, four, three, two, one, one, HAPPY NEW YEAR!

Wait a second! What just happened?

Just before midnight on December 31, 2008, an extra second will be added to the world's clocks. It will mark the 24th time a "leap second" has been used to bridge the gap between the Earth's rotational time and the time kept by highly accurate atomic clocks. The last leap second was inserted at the end of December 2005.

Here's the deal. There are 24 hours in a day. Since there are 86,400 seconds in 24 hours, that means there are 86,400 seconds in a day, right?

Not really. One full rotation of the Earth on its axis—what we call a day—actually takes 86,400.002 seconds. That extra little bit adds up. Like an overgrown hedge, it occasionally needs to be trimmed back. Complicating things somewhat, the Earth's rotation is gradually slowing, making even a negative leap second possible in theory.

So what's the harm of a second here and a second there? The sun rises no matter what the clocks say. How accurate do we really need to get?

Pretty accurate. Clocks based on the pendulum-like electromagnetic frequencies of the cesium atom, such as the NIST-F1 in Boulder, Colorado, will neither gain nor lose a second in 60 million years. The NIST-F1 is one of the prime contributors to Coordinated Universal Time (UTC), a time standard derived from International Atomic Time and corrected to reflect the Earth's rotation.

Modern communications networks rely on UTC. The Internet, cellular phones, and satellite global positioning systems (GPS) are all synchronized to this exacting standard in one way or another. Underwater navigation, air traffic control, deep-space exploration, even law enforcement—these are all areas where every second counts.

But as vital as it has become to modern life, keeping track of UTC is no mean feat. An alphabet soup of international agencies and national laboratories contribute to its maintenance.

The International Bureau of Weights and Measures (BIPM) in Paris, France, calculates International Atomic Time (TAI) from a weighted average of 250 atomic clocks around the world. The International Earth Rotation and Reference Systems Service (IERS) is responsible for announcing leap seconds. In the United States, the job of keeping official time is shared by the Commerce Department's National Institute of Standards and Technology (NIST) and the U.S. Naval Observatory (USNO).

So as you raise your glass to celebrate this New Year's Eve, why not offer a toast to all the dedicated scientists around the world so carefully monitoring the passage of time? Take a moment to savor that extra second.

Maybe you can squeeze in an extra kiss before the ball drops.

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