A "leap second" will be added onto official clocks around the world at midnight to account for the Earth's slowing spin on its axis. Just before we welcome in the New Year, the international authorities charged with keeping precise time will add a single second to our lives. It will be the 24th “leap second” since 1972, and the first since 2005.
Leap seconds are needed to reconcile two very different ways of measuring time. Traditionally, humankind has reckoned time by the spin of the Earth and its orbit around the Sun. Under this astronomical arrangement, a second is one-86,400th of our planet’s daily rotation. But because of tidal friction and other natural phenomena, that rotation is slowing down by about two-thousandths of a second a day.
Since the 1950s, atomic clocks — which are based on the unwavering motions of cesium atoms — have made it possible to measure time far more accurately, to within a billionth of a second a day. Unfortunately, every 500 days or so, the difference between the time registered on those clocks and time as registered by the Earth’s rotation adds up to about ... you guessed it, a second.
So at irregular intervals, the International Earth Rotation and Reference Systems Service, based in Frankfurt, orders that the world’s atomic clocks be stopped for a second. This puts the two systems back in sync — at least until the next leap second.
So then, how will you spend your extra time?
:nytimes, 4 ... 3 ... 2 ... 1 ... 1 ... happy new year!