Mark your calendars—Earth is set to experience its shortest day ever on Wednesday, July 9, 2025. But that’s not all. Two more unusually short days are coming up on July 22 and August 5, all thanks to the cosmic dance between our planet and its lunar companion.
According to recent findings reported by Live Science and confirmed by the International Earth Rotation and Reference Systems Service (IERS), Earth’s rotation on these three days will be slightly faster than normal. This acceleration will shave off between 1.3 to 1.51 milliseconds from the standard 24-hour day.
So, what’s causing this sudden speed-up in Earth’s spin?
The Moon’s Position Is the Key Player
To understand the change, think of Earth as a spinning top. The way the top spins can be altered by how and where it’s nudged. In this case, Earth is being nudged by the Moon—not through a physical touch, but via its gravitational pull.
On July 9, July 22, and August 5, the Moon will be positioned farther from Earth’s equator and closer to its poles. This shift in lunar position changes how gravity interacts with the planet’s axis. As a result, Earth spins ever so slightly faster, making the days a touch shorter than the usual 86,400 seconds.
Why This Matters: A New Kind of Time Correction May Be Coming
While a few milliseconds might seem negligible in our daily lives, it’s a big deal in the world of precise timekeeping. So much so, in fact, that the IERS is considering implementing a “negative leap second” for the first time in history.
This correction, expected around 2029, would mean subtracting a second from the global time standard to realign our clocks with Earth’s true rotation speed.
“This is an unprecedented situation and a big deal,” said Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography, in a quote published by the New York Post. “It’s not a huge change in the Earth’s rotation that’s going to lead to some catastrophe or anything, but it is something notable.”
A Reversal of Long-Term Trends
For most of Earth’s history, the planet has been gradually slowing down, not speeding up. Scientists believe that billions of years ago, a single day lasted only 19 hours. Back then, the Moon was much closer to Earth, and its stronger gravitational pull made our planet spin faster.
As the Moon drifted farther away over time, its influence waned, causing the Earth’s rotation to slow down—leading to longer days.
But that’s not what we’re seeing now. In fact, this isn’t the first time in recent years that Earth has picked up speed. In 2020, scientists recorded a series of faster rotations, with the most notable one occurring on July 5, 2024. On that day, Earth completed its spin 1.66 milliseconds quicker than the usual 24 hours—setting the previous record.
What This Means for the Future
These tiny shifts may not alter how we live our day-to-day lives, but they play a crucial role in global systems that rely on extreme accuracy—such as GPS, satellite communication, and financial markets.
The introduction of a negative leap second would be a historic step in the world of chronometry. While leap seconds have been added in the past to make up for slower rotations, subtracting a second is a brand-new challenge for scientists and engineers.
In the grand scheme of cosmic events, Earth’s slightly faster spin is a fascinating reminder of the intricate forces at play in our solar system—and just how finely tuned our perception of time really is.
