Here's why 2016 will have an extra second

It’s official— the year 2016 will actually be one second longer than originally planned.

At 6:59:59 p.m. EST time on December 31, the world’s official clocks will recognize an extra second, meaning there will be a minute that actually contains 61 seconds. Revelers on New Year’s Eve will have an extra second to sip champagne.

The simple reason that timekeeping experts have decided to insert this extra second, slowing down our official clocks by just a moment, is to keep two different time systems in sync with each other, the U.S. Naval Observatory announced on Wednesday.

Essentially, there is a irregular way of measuring time and a precise one. The irregular one is based on the Earth’s rotation, which actually can slow down (as it is currently doing) based on factors like the tug of the moon. The precise one is based on atomic clocks. To keep them in agreement, experts sometimes add extra seconds to the official time system, slowing it down.

“The basic reason is that compared to time scales that are now defined by atomic clocks, the Earth’s rotation is slowing down,” Geoff Chester, the public affairs officer at the U.S. Naval Observatory, told (Fear not, it’s a “misconception” that the Earth will eventually stop spinning, the Observatory said in a statement.)


“The bottom line is that the Earth— if you are using it to define this fundamental unit of measurement that we call the second— the Earth is a terrible reference because it’s an inherently variable system,” Chester added.

In short, by adding the leap second, official time (measured by atomic clocks) will match the time system measured the Earth’s rotation, called UT1.  The world’s official time system is called UTC, or Coordinated Universal Time, which represents atomic time after the leap seconds have been added to get it to match UT1. This coming leap second will be number 27.

Chester said that inserting the leap second can trouble computer networks, and for that reason they need to provide six months of notice. “Typically, every time we’ve had a leap second inserted since the late 1990s, about 10 percent of the world’s larger computer networks suffer some sort of failure because of this,” he said. He pointed to a disruption that Qantas Airlines faced in 2012 stemming from a leap second; other websites, like Reddit, were affected too.

The added second shouldn’t impact people though, Chester predicted, especially if computer networks smoothly adjust.

And after all, a second isn’t really that long, in real-world terms.

“At the rate that the Earth is currently slowing, in practical terms,” Chester added, “if you’re looking for an extra minute to sleep in in the morning, it will not happen for something on the order of a couple million years.”

The last time a leap second was added was June 30, 2015.

Follow Rob Verger on Twitter: @robverger