You may not have noticed it, but Tuesday, August 5, was, according to scientists, one of the shortest days ever. The day lasted 1.25 milliseconds shorter than the usual 24 hours. That’s because the earth rotated slightly faster around its axis.
A day lasts 24 hours because the earth completes a full rotation on its own axis. Because the earth rotated slightly faster around its axis on Tuesday, that day lasted only 86,399.9875 seconds instead of 86,400 seconds.
It is not unusual for the earth to sometimes rotate a little faster, Professor of Theoretical Astrophysics Vincent Icke (Leiden University) explains to NU.nl. This is because the inner core is constantly moving.
“In the inner core of the earth there are very slow currents of almost liquid matter. As a result, earth’s crusts shift and volcanoes can erupt,” says Icke. These shifts ‘deform’ the earth, as it were. That in turn has an influence on the rotation speed of the earth.
Icke compares the rotation of the earth to a skater making a pirouette. If the skater pulls her arms in, she rotates faster, and if she extends them, she goes slower. “That has to do with the distribution of mass,” says Icke.
The rotation of the earth always fluctuates a bit, but it is striking that the rotation of the earth has accelerated three times this summer. For example, July 10 was 1.36 milliseconds shorter and July 22 was 1.34 milliseconds shorter.
The shortest day ever measured was on July 5, 2024. Then the day lasted 1.66 milliseconds shorter. The rotation of the earth has been measured for hundreds of years and results show that the earth rotates faster than average more often in the summer.
Scientists see that Earth is starting to rotate more slowly
“The average rotation of the earth is quite constant,” Icke emphasizes. It takes hundreds of millions of years before that changes noticeably.
Scientists do notice that the earth is on average rotating more and more slowly. This is due, for example, to the influence of the moon on the earth. For example, the attraction of the moon causes tides on earth. The movement of water masses over the earth in turn has a (small) influence on the rotation of the earth.
“People involved in time measurement don’t immediately start turning all kinds of buttons every time something changes,” Icke continues. There are international agreements that determine when time measurement is adjusted. It can happen that a second is added or subtracted. “That has happened before,” says Icke. “But that is only done when those small changes have accumulated over the years.”
Icke emphasizes that such a change does not matter to most people. “But for navigation systems something like this is very important.”