Earth's rotation is completed faster than normal on some days. July 22 is one of them
Before you get worried, the day will only be 1.34 milliseconds less than the standard 24 hours we're used to, according to Space.com, so it won't be noticeable.
This occurrence is said to be part of a trend in Earth's rotational behavior in recent years that scientists are still trying to understand. If this trend continues, a second might need to be subtracted from atomic clocks around 2029 – known as a negative leap second – which has never been done before.
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The shortest day ever recorded, between 1973 when the atomic clock was invented until 2020, was 1.05 milliseconds less than 24 hours, according to Timeanddate.com.
Since 2020, Earth has continued breaking its speed records. The shortest day ever recorded was on July 5, 2024, when Earth's rotation was completed 1.66 milliseconds faster than usual. The rate of decrease in day length appears to be slowing, according to collected data, but the cause of these recent changes in Earth's rotation remains a mystery.
July 10 was another day this year when Earth's rotation was completed faster than usual, wrapping up in 1.36 milliseconds shy of 24 hours. Aug. 5 is another day predicted to join this phenomenon, clocking in at 1.25 milliseconds shorter than usual.
Why is this happening?
The speed of Earth's rotation used to be much shorter than the 24-hour days we're now used to.
A 2023 study showed that a day on Earth was approximately 19 hours long for a significant part of Earth's early history, due to a balance between solar atmospheric tides and lunar ocean tides. As tidal friction from the moon has caused it to move away from the Earth gradually, the moon takes some of Earth's rotational energy, causing its rotation to slow and days to lengthen, according to Space.com.
So it's not exactly unheard of for the length of days to fluctuate. As for why slightly shorter days have appeared recently, experts are still trying to determine the reason.
Melting polar ice and rising sea levels could be influencing Earth's spin, according to a 2024 study, but rather than being the cause of the acceleration, the redistribution of mass may be moderating it. Other scientists think the culprit is the slowing of Earth's liquid core, which could be redistributing angular momentum in a way that results in the mantle and crust spinning slightly faster.
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An expert who spoke with Timeanddate.com predicts Earth's rotation could soon decelerate again, meaning the recent speeding-up could be a temporary fluke in the planet's long-term trend toward slower rotation and longer days.
Got a tip or a story idea? Contact Krys'tal Griffin at kgriffin@delawareonline.com.
This article originally appeared on Delaware News Journal: Why July 22 will not be a normal 24-hour day, what thi smeans
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