Mechanical watches are getting more and more precise. It is getting down to a deviation of 1-2 seconds per day. But when we compare atomic clocks, which would not deviate a full second in 15 billion years, with the way the Earth actually rotates, the accuracy is much higher: the deviation of the Earth is approximately one second every 18 months or so. Hang on, what do I mean by that? Well, soon after Coordinated Universal Time (UTC) was implemented in the early 1960s, scientists realized that the rotation of the Earth was, on average, not 24 hours per day. Every year the Earth was circa 0.5 seconds slow, clocking in at 31’536’000 and a half seconds for 365 rotations.
Thus, the International Bureau of Weights and Measures, started including leap seconds back in 1972. Ever since, a total of 27 seconds have been added at irregular intervals of 12, 18 or 24 months. They were always added at the end of June 30 or at the end of December 31.
This system was a bit annoying. Especially for computation systems relying on fractions of a second for automatical, interlinked operations. But it worked. Apart from when it didn’t: there are documented temporary crashes on, for instance June 30, 2012, when half the internet experienced slowdowns or crashes when a leap second was added. On a whole however, computation systems can cope with having a second added here and there.
What happened in recent years is somewhat of a surprise. After a steady slow-down, the world is speeding up. But it makes sense: One of the reasons for this is the effect of global warming melting polar icecaps. Just think of a ballet dancer lowering her arms to spin faster.
So, the world’s scientists realized that, if this speeding up was to be compensated for, we’d need to implement a negative leap second by 2029. This has never been done, and the mere concept of this freaked everybody out. Because for reasons that I can’t quite comprehend, it is apparently a LOT more complicated for interlinked computers if a second is removed, than if one is added.
In the end, it came down to a vote among the delegates of the International Bureau of Weights and Measures. The vote was not unanimous, since Russia voted against, and Belarus abstained. But in the end, it was decided that leap seconds are scrapped. So, ending officially on May 20, 2027, leap seconds takes one for the team of humankind, since scrapping leap seconds avoids a potential technological meltdown that could make current Paris riots feel like a breeze.
Of course, the Earth’s irregular movement remain, and it should be accounted for. But instead, the annual or biannual application of a second, the International Bureau of Weights and Measures decided that the world will have to wait until the Earth rotation is one hour off. Then a leap hour will be included to the International Atomic Time. This will occur at the very earliest 1,000 years from now. Today, nobody knows exactly when it will be, but wouldn’t it be cool if a mechanical watch could include leap hours?
FAQ
What is a leap second?
A leap second is an extra second added to Coordinated Universal Time to keep it aligned with the Earth’s actual rotation, which runs slightly slower than a precise 24-hour day.
Why are leap seconds being scrapped?
After decades of slowing down, Earth’s rotation has started speeding up, partly due to melting polar ice caps, making a disruptive negative leap second likely by 2029, which scientists voted to avoid entirely.
When will leap seconds officially end?
Leap seconds will officially end on May 20, 2027, following a vote by delegates of the International Bureau of Weights and Measures, with Russia opposed and Belarus abstaining.
What is a leap hour?
A leap hour is a proposed future correction that would add a full hour to International Atomic Time once Earth’s rotation drifts an hour off, expected no sooner than 1,000 years from now.
