As if the leap day in February wasn't enough stalling for time, scientists intend to delay the arrival of 2009 by one additional second.

Timekeepers will tack on a "leap second" to the world's clocks December 31, 2008 at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC).

The time discrepancy is due to the planet's spin gradually but surely slowing down, mostly due to tidal friction.

Solar timekeeping became somewhat of an antique when atomic clocks made their debut - measuring time on a more stable basis of the microwave signals electrons emit when they change energy levels. But old habits die hard, and mean solar time (UT1) is still used quite frequently to this day.

Under the International Systems of Units, an atomic time-scale second is defined as "equal to the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom."

Leap seconds essentially pause UTC so UT1 can catch up.

The International Earth Rotation and Reference Systems Service (IERS) is in charge of monitoring the difference between the time-scales, and occasionally adding or removing a second to UTC to keep the two consistent.

Since 1972, there have been 24 leap seconds added to the UTC time scale. Leap seconds are inserted in varying intervals from once every six months (15,778,463 seconds) to seven years (220,898,482 seconds).

The most recent leap second was inserted in December, 2005. We suggest you adjust your New Year's eve plans to compensate for the several million yoctoseconds you'll now have to spare. ®

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