On December 31, 2016, a leap second was added to the clock. Leap seconds have been added every so often since 1972. The last one was June 30, 2015. That means the day and year will officially be one second longer, worth, perhaps, an extra sip of champagne.
Leap seconds have been added 26 times since 1972. Why? The length of our day is set by the rotation of the Earth, but Earth’s rotation is not perfectly steady. In fact, Earth’s spin is slowing down because of action of ocean tides, which act like a brake on the spin of the planet.
But then, some events actually speed up the Earth’s rotation, such as the Fukushima earthquake in 2011, which resulted from displacements of portions of the Earth’s crust, shortening the day by 1.6 millionth of a second.
These tiny changes in the calculation in time might not matter much except for telecommunications, which relies on precise timing, and the global positioning system (GPS), which could get off-kilter.
So periodic adjustments are necessary. You can read more about it here.
The bottom line is, in 2016 you got a little more time now to celebrate New Year’s Eve! Happy New Year!