Timekeepers Are Adding a Leap Second to 2016

July 11, 2016 | Erica Tennenhouse

Watch hands at one second to midnight

The year is going to get a bit longer!

2016 is already a leap year, and it’s about to get even longer. Timekeepers at the International Earth Rotation and Reference Systems Service have announced that an extra second will be added on December 31st. After 11:59:59, the clocks will switch to 11:59:60 before hitting midnight.

Leap seconds get added from time to time in order to keep Coordinated Universal Time (UTC) in sync with subtle changes in the Earth’s rotation. UTC, our official measure of time, is defined by atomic clocks that tick at a constant rate based on the regular decay of radioactive elements such as cesium.

SEE ALSO: The Leap Year Explained by Neil deGrasse Tyson

A day should, in theory, contain 864,000 atomic seconds. But in practice, the Earth’s rotation fluctuates slightly due to gravitational effects of the moon, which cause tidal friction that decelerates the spin by around two-thousandths of a millisecond each day.

Eventually, these tiny mismatches accumulate to the point that an additional second needs to be inserted to fill the gap.

A total of 26 leap seconds have been added since the system was first implemented in 1972; the most recent one was added on June 30, 2015.

While most people would never notice a measly second added onto a year, some are calling for leap seconds to be abolished because they can create problems for computer systems.

As Michelle Donahue at National Geographic explains: “To a computer, a minute is always 60 seconds — no more, no less. And in today’s global digital networks, our telecommunication systems can be sensitive to even tiny changes in their internal clocks.”

But for the time being, leap seconds are here to stay. In November, representatives at the World Radiocommunications Conference decided to postpone a final decision on whether to do away with leap seconds until 2023.

In the meantime, leap seconds continue to be announced 6 months in advance, to allow sufficient time for preparation.

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