Earth's rotation only ever slows down; days keep getting longer
The core idea stands, but key numbers or details have changed.
TaughtThe Moon's tidal drag steadily brakes Earth's spin, so every century the day grows a couple of milliseconds longer. That is why we occasionally add a 'leap second'; the planet is always, gradually, slowing down.
NowOn 29 June 2022, Earth completed a rotation 1.59 milliseconds short of 24 hours: the shortest day since atomic clocks began measuring, part of a run of record-fast days since 2020. The planet has recently been speeding up, not slowing.
What actually happened
The long-term tidal slowdown is genuine and still operating. But it is a slow average riding on top of faster wobbles: shifts in the atmosphere, oceans, and molten core can nudge the spin either way, and lately they have been nudging it faster.
The practical twist makes this concrete: timekeepers had only ever added leap seconds to let the clocks wait for a lagging Earth. A planet running fast raises the once-unthinkable prospect of a negative leap second, deleting a second to catch up to the Earth. This is 'updated,' not a myth busted: the physics textbooks weren't wrong about tides, but the flat classroom line 'the day is always getting longer' collided with a decade of records going the other way.
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Sources
- timeanddate.com: Earth Sets New Record for Shortest Daytimeanddate.com
- NASA GSFC: Shortest day in modern timesearth.gsfc.nasa.gov
Who was taught this
Still standard through 2022, so anyone who finished school between 1950 and 2022 learned the earlier version.