Our planet is full of mysteries, and one of the most intriguing recent developments is the inexplicable acceleration of Earth’s spin, leading to some of the shortest days on record. While we often perceive the length of a day as constant, precise measurements reveal a subtle yet significant shift.
The Phenomenon of Shorter Days
On July 9, 2025, for example, the day will be 1.3 milliseconds shorter than average. This isn’t an isolated incident; data from the International Earth Rotation and Reference Systems Service (IERS) predicts that July 22 and August 5 will also experience notably shorter durations this year.
Normally, it takes Earth 24 hours, or 86,400 seconds, to complete one full rotation. However, this rate is not entirely fixed. The IERS continuously monitors these minuscule fluctuations with incredible accuracy to keep high-precision clocks synchronized.
The Moon’s Influence: Tidal Braking
For millennia, the Moon has been the primary external force subtly influencing Earth’s rotation. Through a process known as tidal braking, the Moon’s gravitational pull causes a slight bulge in our planet. This deformation, while responsible for ocean tides, also slowly siphons off momentum from Earth’s rotation, causing our planet to decelerate by approximately 2 milliseconds per century.
This long-term effect is evident when looking back through geological time. During the Triassic Era 200 million years ago, a day was just under 23 hours. Conversely, 200 million years into the future, a day is projected to extend to 25 hours.
Interestingly, when the Moon is furthest from the equator, its braking effect is weaker, leading to slightly longer days. However, the recent trend shows days that are a full half-millisecond shorter than those observed prior to 2020, even on these “weaker braking” days.
Unexplained Acceleration and Its Implications
While seismic events, such as the 9.0 Japan earthquake in 2011 which shortened the day by 1.8 microseconds, can momentarily alter Earth’s rotation, the current trend of accelerating spin remains unexplained. Scientists are still investigating the underlying causes of this recent shift.
Despite the enigma, there’s no need for alarm. The changes are far too small for anyone to notice in their daily lives and will have no catastrophic effects on our planet. Nevertheless, these micro-changes do have practical implications for precise timekeeping.
The ongoing acceleration led the IERS to skip a leap second in 2025, a measure typically added to synchronize atomic clocks with Earth’s slowing rotation. It’s even possible that a leap second might need to be “taken back” in 2029 if the trend continues.
Ultimately, this acceleration is unlikely to be a permanent shift. Experts anticipate that Earth will eventually revert to its long-term pattern of gradually winding down. The mystery of the accelerating spin, however, serves as a fascinating reminder of the dynamic forces at play on our planet.
