December 31, 2016 was one second longer than any other day last year. What did you do with that extra second?
What is known as a Leap Second was added to Earth time on Saturday.
This is similar to a Leap Year when February 29th is added to the calendar to account for the 365 1/4 days the Earth takes to get around the Sun.
That extra 1/4 day would go unaccounted for unless we had a Leap Year.
This is not the first Leap Second we’ve had; in fact, it’s the 27th time we’ve added a second.
The Leap Second was added at midnight Greenwich Mean Time (7PM Eastern Standard Time).
Saturday’s Leap Second made up for the fractions of a second changes the Earth undergoes while spinning about its axis.
Unlike a Leap Year, which occurs every four years, a Leap Second is announced only 6 months ahead of time.
Rotational changes vary, so we can’t predict them as easily ahead of time.
The only reason we add the second is to keep up with atomic time, which is the international standard for keeping time in sync with the Earth’s rotation.
If you really want to get super-technical, an atomic second is 9,192,631,770 oscillations of a cesium-133 atom.