Aug. 5 might be one of the shortest days of the year: Here's why
Scientists predict Aug. 5 just might be one of the shortest days of 2025.
On Tuesday, Earth may rotate up to 1.25 milliseconds faster, according to an updated prediction shared on Timeanddate.com.
Multiple factors can contribute to changes in Earth's rotation rates, including atmospheric wind currents, the position of Earth's seas, and the position of the moon.
Jason Nordhaus, an associate professor of physics at Rochester Institute of Technology in New York, says scientists have been tracking and collecting precise data since the 1960s and 70s that show the length of days has fluctuated over the decades.
"It used to be that the Earth is actually spinning much slower, maybe like, three milliseconds slower per day," Nordhaus told ABC News. "Then, it's been steadily heading in the opposite direction, and then in the last maybe five years, it's really spun up. It's going faster, and so you're getting these shorter days."
Earth's rotational changes are imperceptible to the human eye, said Nordhaus.
"This is nothing anyone would notice," the professor said. "If you wake up in the morning and you look out, you don't know what a millisecond is like."
But the tiny changes can be picked up by the atomic clock, a precise tool scientists use for space navigation and for GPS systems, and the changes are more noticeable over time.
"If you get it wrong and you're off by a millisecond or two milliseconds, I think that works out to be something like, you get your positions off by maybe 50 centimeters to maybe 100 centimeters. And so, then if you accumulate that over the course of a year, you might be off by half a kilometer in your GPS system," Nordhaus explained.
Scientists use the idea of leap seconds to take the changes into consideration, similar to the concept of a leap year.
"If you look back through the '70s to today, there's been something around … 25 or 30 leap seconds have been added to counter all this over time," said Nordhaus.
This summer, there have been three other days – July 9, July 10 and July 22 – where Earth has appeared to rotate more quickly than usual. On July 9, Earth appeared to rotate 1.23 milliseconds faster, 1.36 milliseconds faster the following day and then about 1.34 milliseconds faster on July 22, according to Timeanddate.com.
