The speed of Earth’s rotation seems to be accelerating


Earth seen from space.

Earth seen from space.
Picture: NASA / Reid Wiseman

The year 2020 will be remembered for many things, most of them unpleasant, but will also be remembered for being one of the fastest on record, due to the accelerating speed of rotation of our planet. If this trend continues, it could lead to an unprecedented “negative leap second”.

Our clocks don’t get in sync, but instead of slowing down like they usually do, they start to run a bit fast. The reason is linked to the surprising number of short days experienced last year, the result of the acceleration of the rotation of our planet. so slightly. As time and date reports, 2020 had the shortest 28 days since 1960.

It takes 24 hours, or 86,400 seconds, for the Earth to complete a full rotation around its axis, what scientists call an average solar day. The term “average” is however essential, as slight variations are observed every day. This became evident in the 1960s with the development of atomic time measurement. Atomic clocks measure the Earth’s rotation relative to a distant astronomical object, usually a fixed star. Scientists have learned that the duration of a single day can vary by a few milliseconds (ms), in which 1 ms equals 0.001 second.

The variability in the rotation of our planet is not to be feared, and you certainly don’t have to hold on to your sofa for fear of being thrown in. space. Variability in the speed of Earth’s rotation is a normal phenomenon and is influenced by factors such as the internal sloshing of the molten core of our planet, oceans, winds and atmospheric pressure.

TBe clear, we are talking about very small numbers. Today, for example, should be 24 hours, 0 minutes and 0.0792ms, while yesterday was 24 hours, 0 minutes, 0.2561ms, according to at the time and date, a website run by journalists and researchers. It’s a difference of 0.1769ms, so yes, minuscule stuff. However, some days can be unusual, such as July 5, 2005, when the Earth’s rotation was 1.0516 ms less than the average solar day.

The year 2020 has been quite extraordinary in this regard, breaking the 2005 record no less than 28 times. The shortest of these was July 19, when the Earth’s rotation was 1.4602 ms lower than the average solar day.

Interestingly, we can expect more of the same in 2021. ”[A]n the average of a day in 2021 will be 0.05 ms less than 86,400 seconds “, reports Time and date, which means that over the course of the whole year, “atomic clocks will have accumulated a lag of about 19 ms”.

Typically, these clocks run rapidly by a few hundred milliseconds each year, which requires a added a leap second to keep the clocks in sync.

“A leap second is a second added to Coordinated Universal Time (UTC) in order to keep it synchronized with astronomical time,” according to at the U.S. National Institute of Standards and Technology. “UTC is an atomic time scale, based on the performance of atomic clocks that are more stable than the rate of rotation of the Earth.”

The last time this happened was in 2016. Leap seconds are usually added to the stroke of midnight on New Years Eve, so if you celebrated back then and didn’t wait another second, you kicked off 2017 a bit prematurely.

We didn’t have to invoke a second jump since 2016, and given the acceleration of the Earth’s rotation, we may need to do something we’ve never done before, namely to take away 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 phase with our atomic clocks. That said, the International Earth Rotation Service and Reference Systems, who decides on these matters, currently has No project do this.

It could happen, however. And if we have to summon a negative leap second at some point, you can impress your friends by ushering in the new year exactly one second before everyone else. You are welcome.

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