WASHINGTON – Already a leap year, 2016 will drag on a bit longer. International timekeepers are adding a leap second at year’s end.

A normal day should contain 864,000 atomic seconds – at least in theory.

But, because Earth is slowing down a tad, occasionally timekeepers insert another second or two to match Earth’s rotation and the precise atomic clocks.

U.S. Naval Observatory’s Geoff Chester says the tides’ interaction with the moon and other factors, including warmer, denser waters from El Niño, cause Earth to take longer to go full circle each day.

Timekeepers announced that on Dec. 31, at 11:59 p.m. and 59 seconds Universal Time (6:59 p.m. Eastern Time), the next second will become 11:59:60.

That means the new year won’t start for another second.

A total of 26 leap seconds have been added since the system was first implemented in 1972 by the International Earth Rotation and Reference Systems Service. The most recent one was added on June 30, 2015.

Some scientists want to stop the adding of leap seconds because it can cause problems with computers.