Does the speed of rotation ever slow down in space?

In 2020 the earth turned faster than it has been in a long time

  • According to measurements, 2020 was one of the shortest years since records began.
  • The rotation of the earth accelerated compared to the other measurement years. 28 of the shortest days since 1960 all happened in 2020.
  • The Earth's rotation could even accelerate further in 2021. It would make the days even shorter.

For many, 2020 couldn't end quickly enough. What they probably did not know: The rotation of the earth made this wish come true. 2020 was the shortest year in decades - even if it didn't always feel that way.

According to experts, the 28 fastest days since 1960 all happened in the past year, as the earth rotated around its axis up to 1.5 milliseconds faster than usual. Those 28 days all broke the previous record for the shortest day ever recorded: July 5, 2005. That day was 1.0516 milliseconds shorter than the standard value of 86,400 seconds - and in 2020 the shortest day ever recorded was 0.45 milliseconds less than the previous record.

It's not uncommon for individual days on Earth to be longer or shorter than average at times, thanks to the activity of the Molten Core, the oceans, and the planet's atmosphere. According to, the large number of shorter days in 2020 could be a sign that the earth's rotation is accelerating overall.

Scientists who monitor the speed of the earth predict that 2021 is likely to be even shorter. The average day is expected to be 0.05 milliseconds shorter than the standard length of a day as determined by our clocks. Individual days could even take 1.5 milliseconds less. Over the course of a year, the shorter days are expected to hit a deficit of around 19 milliseconds.

"The earth is now rotating faster than ever before in the last 50 years," said the physicist Peter Whibberley of the British National Physics Laboratory to "The Telegraph".

The earth's rotation has been sluggish for the most part since it was recorded

To determine the length of a day on earth, scientists from the International Service for Earth Rotation and Reference Systems (IERS) measure the exact moment at which a fixed star passes a place in the sky. They express this measurement as universal time and then compare it to atomic time, a time scale calculated using ultra-precise atomic clocks. This comparison can show how much the earth's rotational speed deviates from the norm.

According to IERS, the earth has slowed down overall, rather than accelerating, over the past few decades. Since measurements began in the late 1960s, the average days for most years have been over 86,400 seconds and a few hundred milliseconds.

Scientists offset the slight excess by adding a leap second to the end of the year. In total, around 27 leap seconds have been added since 1972.

However, no new leap second has been added since 2016. Should 2021 be as short as 2020, the scientists could even subtract a second instead.

"It is entirely possible that a negative leap second is required if the rate of rotation of the earth continues to increase, but it is still too early to make a prediction," Whibberley told The Telegraph.

If 2021 goes as expected, it will break the 2020 record again. The last time a year was below the average day length of 86,400 seconds was a while ago: it was in 1937.

This article was translated from English by Klemens Handke. You can find the original here.