The year 2020 will be remembered for many things. Now, you can add Earth’s rotation rate to the list. That’s right, Earth is spinning faster than has ever been recorded.
Accurate satellite measurement began in the late 1960s and early 1970s. The 28 fastest days on record all occurred in 2020.
On average, Earth rotates once every 86,400 seconds, which equals 24 hours, or one mean solar day. But according to TimeandDate.com, 2020 had the shortest days ever measured.
The website says, “Before this year began, the shortest day since 1973 was July 5, 2005, when the Earth's rotation took 1.0516 milliseconds (ms) less than 86,400 seconds. But in the middle of 2020, the Earth beat that record no less than 28 times. The shortest day of all came on July 19, when the Earth completed its rotation in 1.4602 ms less than 86,400 seconds.”
According to LiveScience.com, “Earth is completing its revolutions around its axis milliseconds quicker than average. That's not particularly alarming — the planet's rotation varies slightly all the time, driven by variations in atmospheric pressure, winds, ocean currents and the movement of the core."
But it is inconvenient for international timekeepers, who use ultra-accurate atomic clocks to meter out the Coordinated Universal Time (UTC) by which everyone sets their clocks. When astronomical time, set by the time it takes the Earth to make one full rotation, deviates from UTC by more than 0.4 seconds, UTC gets an adjustment.
Timekeepers have only ever “added” a leap second to our time. That’s because the trend of Earth has been a slowing rotation.
The National Institute of Standards and Technology (NIST) says they’ve added a leap second about every year and a half. The last addition was on New Year’s Eve in 2016.
So what is expected in 2021? Scientists say to expect the trend of having shorter days in 2021 as well.
TimeandDate.com says that according to their calculations, an average day in 2021 will be 0.05 ms shorter than 86,400 seconds. Over the course of the entire year, atomic clocks will have accumulated a lag of about 19 ms. The year 2021 is predicted to be the shortest in decades.
The last time that an average day was less than 86,400 seconds for an entire year was in 1937.
It's possible that at some point in the future, a negative leap second will be needed if the Earth's rotation rate continues.
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