Excited for 2017? You may have to wait one second longer than usual this time to welcome the new year. The world’s timekeepers have decided to add an extra “leap second” to the last minute of 2016, making the last minute longer than every other minute of the year. There are 86,400 seconds in 24 hours. But technically, the Earth takes 86,400.002 seconds to complete a full rotation. So, a leap second gets added every few years to keep time as accurate as possible.

Leap Second 2016 atomic clock
Image Credit: SplitShire / Pixabay

Why leap second?

These extra seconds are not uncommon. They are added either on June 30th at the stroke of midnight or on December 31st of a given year. The latest leap second was added in June 2015. The extra second helps account for inconsistencies between the Earth’s natural rotation speed and the ridiculously accurate atomic clocks that timekeepers use.

The US Naval Observatory said in a statement that a leap second would be added to the world’s clocks at 23:59:59 Coordinated Universal Time (UTC), which corresponds to 6:59:59 PM EST. The UTC is computed at the International Bureau of Weights and Measures in Paris. The International Earth Rotation and Reference Systems Service (IERS) monitors the difference between the Earth’s natural rotation and atomic clocks.

The IERS inserts or removes leap seconds from UTC whenever necessary to keep the two within 0.9 seconds of each other. Historically, time was based on our planet’s mean rotation relative to celestial bodies. But the Earth’s rotation may vary due to several factors including the tidal friction as the moon’s gravity tugs on our oceans.

Atomic clocks lose one second in 100 million years

In contrast, the atomic clocks are incredibly accurate. The atomic time is independent of the Earth’s rotation. It is based on the vibration of the cesium atoms that oscillate at 9,192,631,770 times per second. The atomic clock in Boulder, Colorado is estimated to lose just one second every 100 million years. However, humans began to measure time with such a high degree of accuracy only recently.

When the atomic clock system was instituted in 1972, the difference between UTC and International Atomic Time was 10 seconds. Since then, 26 additional leap seconds have been added at various intervals to keep the two clocks in sync. Scientists have determined that the difference between atomic time and Earth rotation time is roughly one second after every 500-750 days.

What should you do with your clocks?

You are not required to do anything. Organizations writing timekeeping software ensure that the leap second doesn’t cause any trouble to people. Devices that set times automatically such as computers and smartphones will add the leap second on their own. And most people don’t track time precisely enough to notice the one-second different on other clocks.