The year 2020 will be remembered for many things, most of them are unpleasant, but it will also be remembered as one of the fastest ever, because of the accelerating rotational speed of our planet. Should this trend continue, it could result in an unprecedented “negative leap second”.
Our clocks are out of sync, but instead of running slow as usual, they start running a little fast. The reason for this has to do with the surprising number of short days experienced last year, the result of our planet’s once accelerated spin. so a little. As time and date reports, 2020 had the 28 shortest days since 1960.
It takes Earth 24 hours, or 86,400 seconds, to make a full rotation around its axis, what scientists call an average solar day. However, the term ‘average’ is key as there are slight differences every day. This became evident in the 1960s with the development of atomic timekeeping. Atomic clocks measures the rotation of the Earth relative to a distant astronomical object, usually a fixed star. Scientists have learned that the length of a single day can deviate by a few milliseconds (ms), with 1 ms equal to 0.001 second.
The variability in the rotation of our planet is nothing to worry about, and you certainly don’t have to hold on to your couch for fear of being thrown in space. The variability of the Earth’s rotational speed is a normal phenomenon and is affected by factors such as the internal sloshing of our planet’s molten core, oceans, wind and atmospheric pressure.
T.o be clear, we are talking about very small numbers. For example, today is expected to last 24 hours, 0 minutes, and 0.0792 ms, while yesterday lasted 24 hours, 0 minutes, and 0.2561 ms, according to time and date, a website managed by journalists and researchers. That’s a difference of 0.1769 ms, so yes, minuscule things. However, some days may be unusual, such as on July 5, 2005, when the Earth’s rotation was 1.0516 ms less than the average solar day.
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The year 2020 was quite exceptional in this regard, beating the 2005 record a whopping 28 times. The shortest of these was on July 19, when the Earth’s rotation was 1.4602 ms below the mean solar day.
Interestingly, we can expect more of the same in 2021. “[A]One average day in 2021 will be 0.05 ms shorter than 86,400 seconds, ” reports Time and datewhich means that over the year “atomic clocks have built up a delay of about 19 ms.”
Typically, these clocks run fast for a few hundred milliseconds every year, for which one added leap second to keep clocks in sync.
“A leap second is added one second to Coordinated Universal Time (UTC) to keep it in sync with astronomical time,” according to from the US National Institute of Standards and Technology. “UTC is an atomic timescale, based on the performance of atomic clocks that are more stable than the Earth’s rotational speed.”
The last time this happened was in 2016. Leap seconds are usually added at the stroke of midnight on New Year’s Eve, so if you were fourth at that time and did not wait an extra full second, you ushered in 2017 a bit prematurely.
We didn’t have to rely on one leap second since 2016, and given the acceleration of the Earth’s rotation, we may eventually have to do something we have never done before, namely: take a full second. In other words, a negative leap second.
This action would serve the same purpose as a positive leap second, which is to keep UTC in line with our atomic clocks. That said, the International Earth Rotation and Reference Systems Service, who decides on such matters, currently has no plans to do that.
However, it can happen. And should we call in a negative leap second at some future point, you can impress your friends by ringing in the new year exactly one second ahead of everyone else. You’re welcome.