You can toot your New Year's horn an extra second this year, say physicists at the National Institute of Standards and Technology (NIST). Along with the rest of the world's atomic timekeepers, NIST's time and frequency experts will insert a second (known as a leap second) into their time scale on Dec. 31 for the first time in seven years.
From 1972 (when the world went to the current system of atomic timekeeping) until Dec. 31, 1998, 22 seconds were added to Coordinated Universal Time (the official world time known as UTC) to keep it in sync with the Earth's rotation (which can speed up or slow down due to many factors). Since 1999 until recently, that rotation and UTC had stayed closely enough in harmony to not require the adjustment of adding a leap second.This year's leap second will be implemented by adding an extra second to atomic clocks at NIST in Boulder, Colo., and other sites around the world. Normally, the last second of the year would be 23:59:59 UTC on Dec. 31, 2005, while the first second of the new year would be 00:00:00 UTC on Jan. 1, 2006. The leap second will be added at 23:59:59 UTC (06:59:59 p.m. Eastern Standard Time) on Dec. 31, so that atomic clocks will read 23:59:60 UTC before changing to all zeros.
A recent proposal to eliminate leap seconds altogether in the future is still under consideration by the international bodies in charge of coordinating world time.