Why July 9 will likely be one of the shortest days in recorded history

Yahoo

10-07-2025

The Brief
July 9 is expected to be one of the shortest days in history, but you won't notice a difference.
The Earth has been moving faster in recent years, and scientists aren't exactly sure why.
Today could be the shortest day you've ever experienced – but it'll happen faster than the blink of an eye.
Thanks to the moon's distance from the equator, July 9 could be as much as 1.30 milliseconds – or more – shorter than the usual 86,400 seconds, or 24 hours, in a day.
By the numbers
There are 86,400 seconds in a day (24 hours), "give or take a millisecond or so," astrophysicist Graham Jones wrote for TimeAndDate. That's how long it takes for Earth to make one full rotation on its axis.
A millisecond is one-thousandth of a second. For context, the blink of an eye usually takes about 100 milliseconds.
Jones says there's only one way to measure the millisecond variations for Earth's axis: atomic clocks. The number of milliseconds above or below 86,400 seconds is known as length of day (LOD).
The backstory
Since the dawn of time, Earth has been gradually rotating slower, which makes our days longer. According to LiveScience, 1 to 2 billion years ago, a day on Earth was 19 hours long.
Before 2020, the shortest length of day variation measured by an atomic clock was -1.05 milliseconds – meaning the Earth rotated 1.05 milliseconds faster than 86,400 seconds.
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Earth's been moving faster ever since.
So far, the shortest day ever recorded was July 5, 2024, when Earth rotated 1.66 milliseconds faster than usual. This year, scientists predict three shorter days in July and August. On July 9, the day is expected to be 1.30 milliseconds shorter, followed by an even shorter -1.38 milliseconds on July 22 and a -1.51 milliseconds on Aug. 5.
Dig deeper
According to LiveScience, for those three days in July and August, the moon will be at its farthest distance from the equator. That changes the gravitational pull of Earth's axis.
What they're saying
"Think of the Earth as a spinning top — if you were to put your fingers around the middle and spin, it wouldn't rotate as quickly as if you were to hold it from the top and bottom," science writer Amy Arthur explained in LiveScience.
Still, scientists are baffled as to why Earth has been accelerating in recent years. How fast Earth spins is dependent on a number of factors, including the motion of Earth's core, oceans and the atmosphere, TimeAndDate reports.
Why you should care
According to The Guardian, computers, servers, GPS systems, banking and utility networks all rely on extremely synchronized clocks. If the clocks are off by even a fraction of a billionth of a second, it could affect those systems.
The Source
This report includes information from TimeAndDate, LiveScience and The Guardian.