Earth is currently rotating slightly faster on its axis than usual. As a result, scientists say that this coming Tuesday will be one of the shortest days ever recorded: it will be 1.25 milliseconds shorter than the standard 24 hours. That means that instead of 86,400 seconds, Earth will complete one full rotation in just 86,399.9875 seconds. Generally speaking, Earth's rotation is slowing down over the long term.
This is due to the gravitational influence of the Moon, which causes tidal friction that gradually decelerates our planet’s spin. For example, hundreds of millions of years ago, a day lasted only 22 hours, and it is expected that, millennia from now, a day may last even longer than our current 24-hour cycle. However, in recent years, scientists have noticed an unexpected acceleration in Earth’s rotation — a reversal of the historical trend.
Tuesday will mark the third such rapid spin this summer, following peaks on July 10 (-1.36 milliseconds) and July 22 (-1.34 milliseconds). In fact, Earth has broken several "speed records" in recent years. Before 2020, the shortest day ever recorded was just 1.05 milliseconds shorter than 24 hours. But in 2020 alone, scientists recorded the 28 shortest days since measurements began in the 1960s.
The shortest day on record occurred on July 5, 2024, when the Earth’s rotation was 1.66 milliseconds faster than usual. These measurements are carried out by the International Earth Rotation and Reference Systems Service (IERS). Earth's rotation does not align precisely with the 24-hour solar day assigned by atomic clocks, which led to the introduction of the leap second in 1972. Whenever the Earth’s rotation deviates from atomic time by more than one second, scientists pause clocks for one second — typically on June 30 or December 31 at 11:59 p.m. — to realign the systems. The last time this occurred was on December 31, 2016.
GPS and Financial Systems at Risk
Since then, leap seconds have not been necessary because Earth’s rotation has been speeding up, not slowing down. Now, scientists are even considering the possibility of a negative leap second, which would be unprecedented. This could pose significant risks to modern systems that rely on extreme time precision. GPS navigation, internet connections, stock market algorithms, and communication satellites all depend on time measurements accurate to the millisecond.
Even minor discrepancies could result in delays, data errors, or system failures. The exact cause of this increased rotation speed remains unknown. Scientists are puzzled, but several hypotheses are being investigated. These include internal Earth processes such as convection currents in the liquid iron core, as well as external influences like ocean currents, high-altitude atmospheric wind patterns, climatic effects like El Niño, seismic activity, and mass loss from melting glaciers. For now, scientists continue to monitor Earth's spin with increasing scrutiny, as even the smallest shift in our planet's rotation could have major technological implications on a global scale.
