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Secret Seconds

Since 1972, scientists have been quietly adding seconds to our clocks because - don’t panic - the earth is slowing down. No, we’re not going to grind to a stop. The tiny fluctuations just mean we’re a bit ‘wobbly’. But, it’s small enough to f**k with our timepieces. According to NASA, our days are two milliseconds longer than they were in 1820. How did they notice? They invented the atomic clock.  Until the invention of the atomic clock in the early part of the 20th century, the earth’s rotation was used to measure seconds, minutes and hours. While this seems like a foolproof system, the earth isn’t that steady. Atomic clocks produce a much more consistent and reliable result by using the electromagnetic vibrations of cesium atoms. One day is 86,400 seconds, but the atomic clock records the earth's rotation at 86,400.002 seconds. This tiny discrepancy compounds over time and - after a year - adds up to one second.

The International Earth Rotation and Reference Systems Service (IERS) is in charge of popping in the extra second when we need it. But they don’t add seconds every year (this is where things get a bit squiffy). The earth’s rotation is impacted by the pull of the moon and the sun. This tug of war creates fluctuations in the earth’s speed making its rotation fairly inconsistent. For example, 21 leap seconds were added between 1972 and 1998, compared to only four between 1998 and 2018. Furthermore, the calculations are made in conjunction with the earth’s position in relation to objects in the observable universe. The added seconds are a way to better align the atomic measurements with the measurements from space.

So after all that, do we really need them? It’s debatable. Adding seconds can mess with sensitive electronic equipment, like the computers used in stock markets, which rely on very precise timings. Some have suggested we bank all the extra seconds and add an hour every couple of centuries. But who’s passing on that message? And, at the end of the day, time is a construct. 

Curious to learn more?

Leap second to be added December 31

A very short history of the Leap Second

U.S. Naval Observatory Press Release: 2016 will be one second longer

Image by Pierre Bamin


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