Earth is set to spin a bit faster in the coming months, leading to slightly shorter days, according to scientists. On July 9, July 22, and August 5, the effect will be most noticeable, with each day ending up between 1.3 and 1.51 milliseconds shorter than usual. The shift comes down to the moon's position relative to Earth's equator, which changes how its gravity interacts with our planet's axis, LiveScience reports. Normally, a day lasts about 86,400 seconds, or 24 hours, but Earth's rotation isn't completely steady. It's influenced by factors like the sun and moon's positions, movements in Earth's magnetic field, and even changes in where mass is distributed on the planet.
Historically, Earth spun faster: one to two billion years ago, a day lasted just 19 hours, thanks in large part to a closer, and more influential, moon. Over time, as the moon moved further away, its grip on Earth's spin weakened and the days gradually lengthened. But scientists have noticed fluctuations in recent years. In 2020, Earth was spinning faster than at any point since record-keeping began in the 1970s. The shortest day ever recorded—1.66 milliseconds less than 24 hours—came on July 5, 2024.
The upcoming short days are tied to the moon reaching its furthest point from Earth's equator, which lessens its slowing effect on the planet. When the moon is closer to the poles, Earth's spin speeds up, similar to how a spinning top moves faster if grasped at the ends. Global timekeepers occasionally add "leap seconds" to keep atomic clocks accurate but they might have to subtract one if the spinning keeps up, Michael Wouters at Australia's National Measurement Institute tells the Guardian. "People do not expect time to go backwards," he says, but with changes of a few seconds over a century, "nobody's really going to notice."
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