Some folks are going to have to add an extra second to their upcoming New Year's countdown.
The Earth takes 365.2422 days to go around the sun, so every four years we add Feb. 29 to the calendar to make up for the quarter day that goes unmarked. But there are other forces at work that require our attention.
Because of this, a new second will be added Dec. 31 at 11:59:59 Coordinated Universal Time -- 6:59:59 pm Eastern, reports Live Science.
Time was once based on the rotation of the Earth relative to the sun, from which the second was derived. But the advent of atomic clocks changed the all that, with seconds being based electron emissions within an atom.
International scientists then established two timescales in 1970. One is based on the rotation of the Earth, the other on atomic time.
But the Earth's speed across the heavens has been gradually slowing, meaning that "Earth years" are running longer and longer, while "Atomic years" remain constant. To keep the two clocks in sync, a "leap second" is occasionally added to Atomic time.