Earth’s rotation around its axis has been speeding up over the past few decades. Since this determines how long a day is, this trend has been making our days shorter. It turns out that a day is very rarely exactly the magic number of 86,400 seconds.

In June 2022 we set a record for the shortest day over the past half a century or so. This stuffs up GPS and other precision technologies.

A 24 hour day is apparently a new thing for the earth. A few billion years ago, an Earth day was only about 19 hours which was hardly enough time to do anything.

For the past 20,000 years, another process has been working in the opposite direction, speeding up Earth’s rotation. When the last ice age ended, melting polar ice sheets reduced surface pressure, and Earth’s mantle started steadily moving toward the poles.

Just as a ballet dancer spins faster as they bring their arms toward their body – the axis around which they spin – our planet’s spin rate increases when this mass of mantle moves closer to Earth’s axis. This process has been shortening each day by about 0.6 milliseconds each century.

Earth reached its shortest day on June 29, 2022, the long-term trajectory seems to have shifted from shortening to lengthening since 2020. This change is unprecedented over the past 50 years.

Scientists have speculated this recent, mysterious change in the planet’s rotational speed is related to a phenomenon called the “Chandler wobble” which has nothing to do with too many people watching reruns of friends but a small deviation in Earth’s rotation axis with a period of about 430 days. Observations from radio telescopes also show that the wobble has diminished in recent years.