Scientists expect Wednesday, July 9, to be the shortest day of 2025, running just over a millisecond faster than the standard 24-hour cycle, according to a report by USA Today. A day is generally supposed to be 86,400 seconds.
That’s the textbook version. But Earth doesn’t always behave that precisely. Sometimes it speeds up a touch. Sometimes it drags. In fact, the shortest day ever was reportedly recorded not very long ago. It was on July 5, 2023, when Earth completed its spin 1.66 milliseconds faster than normal.
Before that, the record was from 2005, but in recent years, new records have kept popping up.
Also read: Spin cycle: Why Earth’s rotational speed is changing
What’s causing the shift?
A mix of things that includes internal changes in the planet, atmospheric movement, ocean currents and the Moon, especially its position relative to the equator. It can tweak Earth’s rotation just enough to show up on high-precision instruments, informs USA Today.
Astrophysicist Graham Jones explained this recently. He noted that climate change might even be contributing, with melting glaciers and vanishing groundwater subtly altering Earth’s mass distribution.
Three dates to watch out for this summer
{{/usCountry}}Astrophysicist Graham Jones explained this recently. He noted that climate change might even be contributing, with melting glaciers and vanishing groundwater subtly altering Earth’s mass distribution.
Three dates to watch out for this summer
{{/usCountry}}Scientists say three days this season are going to be slightly shorter than average:
July 9 – 1.30 milliseconds shorter
July 22 – predicted to lose 1.38 milliseconds
August 5 – may run 1.51 milliseconds fast
Live Science reports that it happens when the Moon is furthest from the equator, pulling differently on Earth’s spin axis. That tiny difference is enough to speed things up a bit, just enough for scientists to notice.
Shortest day: why does it matter?
People might not care about a lost millisecond, but atomic clocks do. These clocks keep the world’s digital infrastructure running. From GPS systems to internet servers, they rely on ultra-precise timekeeping.
“If clocks get thrown off by even a little, the entire network could feel the effects,” physicist David Gozzard told The Guardian.
That’s why researchers track Earth’s spin so closely. And ever so often, to keep things aligned, they add or remove what’s known as a leap second.
It’s not a big deal for daily life, but in the background, scientists are watching the clock tick.
FAQs
1. Will the Earth spin faster on July 9?Yes, scientists predict Earth’s rotation will slightly accelerate on July 9, causing the day to be marginally shorter than usual.
2. Is July 9, 2025 the shortest day?It is expected to be the shortest day of 2025 so far, running approximately 1.3 milliseconds less than a standard 24-hour cycle.
3. Why is today the shortest day ever?Earth’s rotation can vary due to natural forces like lunar gravity and internal geophysical changes, which occasionally shorten the day by milliseconds.