WASHINGTON - For those obsessed with keeping proper time, don't forget to set your clocks ahead at midnight ... by one second.
This Saturday, a "leap second" will be added to the clock at midnight universal time (4pm Pacific). After 11:59:59 PM, the clocks will roll to 11:59:60. Why? A combination of factors.
The earth is spinning a little slower than it used to, courtesy of the moon's gravitational tug, making each day about two milliseconds longer than it was a century ago. So every few years, the clocks are corrected to synchronize with official U.S. atomic clocks.
There are no noticeable side effects from the change. The last leap second was tacked on to atomic clocks in January 2009. Another one shouldn't be necessary until 2015.
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