Earth Slows Down, but Remains Unpredictable
By Graham Jones. Published 25-Apr-2024RSS

Following a recent run of the shortest days ever recorded by atomic clocks, Earth’s rotational speed may be slowing.

Earth’s Acceleration Ends
In the past few years, Earth’s spin speeded up. It was at its swiftest in June 2022, which included the shortest-ever days as measured by atomic clocks.

Since then, however, the trend has reversed. In 2023, for the first time in seven years, the average length of day became longer. Meanwhile, the latest predictions suggest this slowdown may continue into 2025.

Review: Earth Speeds Up
In general, Earth’s rotational speed is decreasing: around 100 million years ago, a day on Earth was only 23 hours long. This gradual slowdown is caused by the gravitational pull of the Moon acting as a gentle brake on Earth’s spin.

However, during the past decade, Earth speeded up. Here at timeanddate, we kept a close eye on this development—and its consequences.

2023 and 2024: Earth Slows Down
The speed of Earth’s daily rotation is recorded as a number called ‘length of day’. This number is the difference between (a) the time it takes Earth to spin once on its axis with respect to the Sun, and (b) 86,400 seconds (which equals 24 hours).

Look up length of day for today or any other date

The following table shows the average length of day in milliseconds (ms) for the years 2016 to 2024. The average decreased from +1.34 ms in 2016 to a minimum of -0.25 ms in 2022. But the average day lengthened to -0.08 ms in 2023, and is predicted to be longer again in 2024.

https://www.timeanddate.com/news/astronomy/earth-rotation-2024