CA could see one of shortest days on record in August. What’s causing time shift?
California is set to experience one of its shortest days on record — and, no, it’s not because summer is winding down in the Northern Hemisphere.
The Earth’s full rotation on its axis is gaining speed, resulting in the planet’s quickest-ever days, according to online calendar Time and Date.
Earth is predicted to undergo another fast turn on Tuesday, Aug. 5.
Acientists estimate Tuesday will be 1.25 milliseconds shorter than the typical 24 hours — or, 86,400 seconds — that make up a day on Earth, according to Time and Date.
Here’s what to know about the strange phenomenon that’s affecting our planet’s rotation.
How long is a normal day on Earth?
People live by the 24-hour solar day on Earth.
In this time span, the planet completes a full spin around its axis, with the sun making a circle across the sky, according to EarthSky.
Earth is an “almost-but-not-quite-perfect timekeeper,” Time and Date said, meaning that each and every day is 86,400 seconds, plus or minus a millisecond.
Humans won’t normally notice the occasional shortening of the day since a single millisecond equals 0.001 seconds — about 100 times faster than the blink of an eye, according to Time and Date.
However, scientists have been keeping track of the length of days since the 1950s by using atomic clocks, which are “among the most accurate timekeeping devices in history,” the online calendar said.
When were shortest days on record in 2025?
Scientists have recently measured some of the shortest days ever on record.
Before 2020, the shortest day ever recorded was 1.05 milliseconds less than the standard 24-hour day.
Since then, “Earth has managed to shatter this old record every year by around half a millisecond,” Time and Date said.
The current record-holder occurred on July 5, 2024, when the day lasted 1.66 milliseconds shorter than usual, according to Time and Date.
A series of quicker-than-normal days were expected in July, with another one expected to happen in August.
Wednesday, July 9, was predicted to be 1.23 milliseconds faster than usual, according to data Time and Date compiled from the International Earth Rotation and Reference Systems Service and the U.S. Naval Observatory.
Thursday, July 10, was set to be the shortest day of the year with a possible 1.36-millisecond reduction from the standard 24-hour day, the data showed.
The actual length of these days had yet to be confirmed as of Monday, Aug. 4, Time and Date said.
The online calendar also predicted Friday, July 22, would be 1.34 milliseconds shorter and Tuesday, Aug. 5, would be 1.25 milliseconds shorter.
Why are days getting shorter on Earth?
Scientists are generally perplexed why Earth’s rotation on its axis is gaining speed on certain days.
Time and Date said that short-term variations on the length of day are impacted by the orbit of the Moon.
“Our planet spins quicker when the moon’s position is far to the north or south of Earth’s equator,” the online calendar said.
However, Earth’s varying spin speed could also be changing due to a number of factors, including the motion of Earth’s core, the oceans and atmosphere, Time and Date said.
“Nobody expected this. The cause of this acceleration is not explained,” Leonid Zotov, an expert on Earth rotation at Moscow State University, told Time and Date. “Most scientists believe it is something inside the Earth. Ocean and atmospheric models don’t explain this huge acceleration.”
A study published in scientific journal Nature in 2024 indicated that climate change may be to blame for the spat of shortened days.
The melting of ice on Earth could be slowing the rotation of its liquid core and causing the planet to spin faster, the study found.
What happens if days keep getting shorter?
“If the situation continues through 2029, a so-called negative leap second could be added — for the first time ever,” Space.com said.
If it becomes necessary to slow astronomical time by a second, that adjustment could cause issues for computers, GPS and telecommunications tools since software systems might assume time only moves forward, National Geographic said.
“The impact of a negative leap second has never been tested on a large scale,” Meta engineers warned in a 2022 report. “It could have a devastating effect on the software relying on timers or schedulers.”
This story was originally published August 5, 2025 at 8:00 AM.
