It looks like 2016 is going to stick around for a little longer this year—to be precise, one second longer. The extra second being tacked on to the year is known as the leap second and it’s actually not all too uncommon. Since 1972, leap seconds have been added to the calendar every two to three years, totaling 26 adjustments excluding the one coming up later tonight. The reason? To keep our atomic clocks in sync with the Earth’s rotation.
“Atomic clocks are more than a million times better at keeping time than the rotation of the Earth, which fluctuates unpredictably. Leap seconds are needed to prevent civil time drifting away from Earth time. Although the drift is small—taking around a thousand years to accumulate a one-hour difference—if not corrected, it would eventually result in clocks showing midday before sunrise.”
Because the Earth’s rotation can be somewhat erratic, these adjustments don’t come at regular intervals. Earlier this year, the International Earth Rotation and Reference System Service released a bulletin announcing that it would be necessary to add an extra second at the end of December. However, the last adjustment was June 30, 2015 at 23:59:60 UTC.
As we noted in our article about atomic clocks, extreme accuracy—even at an unimaginably tiny scale—is of the utmost importance for managing certain systems (e.g., GPS) that rely on the coordinated worldwide accuracy of atomic clocks. The addition of the leap second helps to maintain such systems.
Last year, our friends at Hodinkee wrote about the Hoptroff wristwatch—a timepiece that uses both mechatronic quartz and atomic movements to automatically account for leap seconds.
To learn more about this year’s leap second, click here.