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New Year to Arrive Late Again This Year: Leap Second to be Added on Dec. 31

As it has many times before, the new year will get off to a late start when it is delayed for exactly one second to allow the world's atomic clocks to be synchronized to the spinning Earth.

The keepers of the U.S. primary standard of time and frequency, the atomic clock at the Boulder (Colo.) laboratories of NIST, will be adding a leap second on Dec. 31, as will the operators of all the other standard clocks around the world. This is the 20th such adjustment to the world's time scale as decreed by the International Bureau of Weights and Measures in Paris.

Leap seconds are needed to keep our clocks (the best of which are now so accurate that they lose or gain far less than a millionth of a second per year) in step with the spinning Earth, which varies several thousandths of a second per day. Since we cannot speed up the Earth, we have to slow down the clocks to keep them "in synch." They are slowed down, in effect, by stopping them for exactly one second every 1 to 2 years, to let the Earth catch up.

This year's leap second will be inserted at 23:59:60 UTC on Dec. 31, 1995. That's the scientific way to say it will happen just before 7 p.m. EST on New Year's Eve. The last minute of the old year will actually be 61 seconds long, and thus the new year will start a second later than it would without the leap second.

For most people, a single second here or there doesn't matter much. But for some, a second is a big deal. Modern television and telephone systems, marine and aviation navigation systems, computer networks, electric power grids, and multitudes of scientific applications are just a few of the kinds of activities that depend on very precise time and frequency. Most of these will have to be adjusted for the leap second. For the rest of us, failure to observe the leap second just means you might kiss your sweetheart a second early on New Year's Eve.

Released December 13, 1995, Updated November 27, 2017