The world is spinning faster for 3 days this summer, scientists say, with Earth having completed its rotation slightly quicker on July 9, and expected to do so again on July 22 and August 5. Though the change is measured in milliseconds, experts say it highlights a deeper shift in how we measure time—and how nature and technology must stay aligned.
On these days, the Earth’s rotation is forecast to shorten each day by just over one millisecond. A standard day is 86,400 seconds long, but slight speedups like these mean the planet will complete its spin a little faster than usual.
The change is not visible to the human eye, but it matters to those responsible for tracking global time. It’s a tiny difference, but one that adds up over time, explained Dr. Michael Wouters, time and frequency lead at Australia’s National Measurement Institute. If the planet continues to spin faster and more frequently, there will be a need to think about how official clocks adjust.
From sun tracking to atomic clocks
Historically, a day was measured by the Earth’s rotation and the sun’s position in the sky. “The Earth rotates once per day, you divide that by 86,400, that’s one second,” Wouters said. This system remained in use until the 1950s, when scientists introduced atomic clocks to define time with far greater precision.
Modern timekeeping now depends on atomic clocks, which measure time down to a nanosecond. These devices are synchronized with Coordinated Universal Time (UTC), the global time standard.
The National Measurement Institute operates several atomic clocks at its Lindfield laboratory in New South Wales. One serves as the official time source, while others monitor its accuracy.
Dr. David Gozzard, a physicist at the University of Western Australia, says exact timing is critical for many technologies, including GPS, communication systems, banking, and power grids. “We’re transmitting data so quickly, and it all needs to be time tagged, so computers know what data goes where,” he said.
Unlike atomic clocks, Earth’s spin is not always consistent. Dr. Gozzard points to gravitational interactions with the moon, which influence tides and slow down the planet’s rotation. When the moon is farther from the equator, that slowing effect weakens slightly.
Seasonal changes and the possibility of time subtraction
Seasonal patterns also play a role, says Dr. Oleg Titov of Geoscience Australia. The shortest days typically occur in July and August, while Earth tends to decelerate between November and March. Since 2020, scientists have observed more frequent short days, with July 5, 2024, marking the fastest day on record, 1.66 milliseconds shorter than average.
To correct long-term differences between Earth’s rotation (known as Universal Time 1) and UTC, timekeepers occasionally add a “leap second.” The most recent was in 2016. But from 2035, international standards will no longer include leap seconds, a change welcomed by Gozzard.
If the Earth continues to spin faster, there could be significant challenges for global timekeepers. Researchers suggest that instead of adding an extra second to account for the planet’s slowdowns, they may need to remove one in the future. This is a potential adjustment that has never been tested before, and the effects it could have on digital systems are still unknown.
While this change may seem significant, it is unlikely to be noticeable for most people. Even though the Earth’s rotation may vary by a few milliseconds, it won’t disrupt daily routines.
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