Earth's Rotation Accelerates, Shorter Days Expected

Wednesday 9 July , Tuesday 22 July and Tuesday 5 August : there are three dates that could set a new record for the shortest day ever measured this summer. The fault lies with the Earth's rotation , which has begun to accelerate since 2020 , imperceptibly shortening the canonical 24 hours of the average solar day by a few milliseconds . Astrophysicist Graham Jones points this out on the Time and Date website. " Our planet is a nearly perfect chronometer , but not quite," says the expert. "On average, the Earth completes a full rotation on its axis in 86,400 seconds (or 24 hours ), with an approximation of about one millisecond ," a fluctuation shorter than the blink of an eye that can only be detected using atomic clocks. Until 2020, the Earth's rotation had gradually slowed down and the shortest day ever recorded had only been 1.05 milliseconds shorter . Then the trend reversed, with the Earth's rotation accelerating , setting new records year after year, especially in the summer months. The shortest days were June 30, 2022 , which lasted 1.59 milliseconds less, and July 5, 2024 , which lasted 1.66 milliseconds less. In 2025, the Earth is expected to approach this record value again around July 9, July 22, and August 5. There are three possible dates because short-term variations in the length of the day are influenced by the Moon's orbit : the Earth's rotation is in fact faster when the Moon is far north or south of the Earth's equator.

It's hard to say why the Earth sped up and when it will slow down again, the astrophysicist points out. "Long-term variations in the Earth's rotation speed are influenced by a long list of factors , including the complex motion of the Earth's core, oceans, and atmosphere."