‘Twenty-six times since 1972, the world’s timekeepers have added a leap second to the clock, the last time being on June 30 of last year, when the day got a little longer, even if you might not have noticed.
It’s going to happen again this year, according to the Associated Press, with the leap second added to the final day of 2016, when the clock will strike 11 hours, 59 minutes, and 59 seconds. Ordinarily the next tick would be midnight, but timekeepers said this year it will be 11:59:60, before turning over to 12:00.
The leap second isn’t necessary on some years, if the Earth orbits more quickly around the Sun. But an official from the U.S. Naval Observatory told the AP that the Earth was a bit slower around the Sun this year, in part because of El Niño…’
Source: Atlas Obscura