Our planet set a record for completing one rotation faster than scientists had ever previously recorded, according to TimeAndDate.com. Earth rotated once around its axis on Wednesday, June 29, in 1.59 milliseconds less than 24 hours.
Hang on! Earth takes exactly 24 hours to rotate once on its axis, right? Almost, yes, but not exactly.
What about the ‘leap seconds?’
Until a few years ago it had been thought that Earth’s rotation was slowing down after several successive measurements by atomic clocks since 1973.
The International Earth Rotation and Reference Systems Service (IERS) had even begun adding leap seconds every now and again to make up for the slower spin (it last happened on December 31, 2016).
Over a longer time period that may still be the case—Earth’s rotation may, in general, still be slowing down.
After all, the Moon is gradually slowing down the Earth’s rotation. Its gravitational pull causes tides and makes the Earth’s orbital path around the Sun slightly elliptical.
How fast is Earth rotating?
However, in the last few years the atomic clocks have shown that Earth rotation is now speeding up. In fact, we could be beginning a 50 year period of shorter days.
In 2020 scientists recorded the 28 shortest days since 1960. Last year that trend did not continue, with the shortest day in 2021 being longer than in the previous year.
However, on June 29, 2022 our planet completed its quickest-ever spin, followed quickly by a day that lasted 1.50 milliseconds less on July 26, 2022.
The previous record for the shortest rotation was July 19, 2020, when the Earth’s rotation took 1.4602 milliseconds less than 24 hours.
Why is Earth speeding up?
The cause of the differing speed of Earth’s spin is unknown, but theories abound:
- The melting of the glaciers means less weight on the poles
- Motions of our planet’s inner molten core
- Seismic activity
- The “Chandler wobble”—the movement of Earth’s geographical poles across its surface
Why Earth’s rotational speed is important
Earth’s quickening rotation has consequences because atomic clocks—which are used in GPS satellites—don’t take into account the Earth’s changing rotation.
If Earth spins faster then it gets to the same position a little earlier. A half-a-millisecond equates to 10-inches or 26 centimetres at the equator. In short, GPS satellites—which already have to be corrected for the effect of Einstein’s general relativity theory (the curve of space and time)—are quickly going to become useless.
There are also potentially confusing consequences for smartphones, computers and communications systems, which synchronize with Network Time Protocol (NTP) servers. It’s defined as the number of seconds since 00:00:00 UTC on January 1, 1970.
To solve all these international timekeepers may need to add a negative leap second— a “drop second.” Though Earth may already be spinning as quickly as it ever will, a slowdown is inevitable.
Only time will tell.
