A stitch in (official) time

2008 will last little longer: Extra second added to reconcile network clocks with Earthly ways

If by New Year's Eve you've felt that 2008 went on for a little bit too long, then you're spidey-sense will have tingled correctly: The international tribunal of time-keepers have tagged an extra second onto the year to make up for the Earth's sluggish rotation.

The extra second, or leap second, will be grafted onto the end of the year, immediately after 11:59:59 PM, Universal Coordinated Time (UCT), Dec. 31. It will be the 86,401st second of the year.

Since UTC is centered on the time-zone of London, England, which resides near the Greenwich Meridian, the extra second will reach the United States earlier, right after 6:59:59 PM Eastern Time. Those visiting the National Institute of Standards and Technology’s Time.gov at that moment will see the extra second (6:59.60 PM) flash by.

System administrators should not have to worry about the extra second if they have their machines periodically synchronize their time via the Internet or some other network synchronized by the Network Time Protocol (NTP). The U.S. Naval Observatory in Washingtonkeeps the official time, which is distributed via NTP to all nodes on the Internet.

The extra second is needed to resynchronize the world's official time with the Earth's orbit, according to a NIST advisory.

Because of a number of influences, the Earth takes ever-so-slightly longer than 24 hours to make one complete rotation, usually by about an additional .0002 seconds. After about 500 days, the accumulated difference between astronomical time and atomic time can be about a second.

Formerly considered 1/86,400th of a day (or complete rotation of the planet), the official duration of the second was periodically altered in centuries past to accommodate the Earth's changing rotational schedule. In 1967, the Thirteenth General Conference on Weights and Measures redefined the second as a specific duration, one defined by an atomic clock and based on a natural resonance frequency of the cesium atom. Since then, the world's official time has been kept by atomic clocks.

Leap seconds are necessary to resynchronize the official atomic clock-derived time in line with what humans feel the time should be — namely, that the sun should be directly overhead at noon, that it should set in the evening, and so on. Without occasional adjustments, the time would drift out of centuries-old astronomically derived perceptions of time.

The International Earth Rotation Service in Paris scheduled the leap second, the 24th added since the practice was started in 1972. The last one occurred on New Year's Eve 2005.

About the Author

Joab Jackson is the senior technology editor for Government Computer News.

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