In the coming weeks, Earth's rotation is expected to accelerate, resulting in some unusually short days. On specific dates—July 9, July 22, and August 5—2025, the gravitational influence of the moon will cause each day to be between 1.3 and 1.51 milliseconds shorter than the typical 24-hour cycle. A complete rotation of Earth takes approximately 86,400 seconds, but various factors can impact this timing.
The speed of Earth's rotation is influenced by several elements, including the positions of the sun and moon, changes to the planet's magnetic field, and the distribution of mass on Earth. Historically, Earth's rotation has been slowing down since its formation, which has gradually lengthened the duration of our days. Research indicates that about 1 to 2 billion years ago, a full day on Earth was only 19 hours long. This phenomenon is attributed to the moon being closer to Earth, resulting in a stronger gravitational pull that accelerated the planet's spin.
As the moon has drifted away over the millennia, days have lengthened. However, recent studies have documented fluctuations in the speed of Earth's rotation. Notably, in 2020, scientists observed that Earth was spinning faster than at any time since the 1970s, with the shortest recorded day occurring on July 5, 2024, which was 1.66 milliseconds shorter than the standard 24 hours, as reported by timeanddate.com.
On July 9, July 22, and August 5, 2025, the moon will be positioned at its furthest distance from Earth's equator. This positioning alters the gravitational impact on Earth's tilt and rotation. To visualize this, consider Earth as a spinning top; holding it from the top and bottom allows for a faster spin compared to gripping it in the middle. When the moon is closer to the poles, it enhances the spin speed of Earth, resulting in shorter days.
While natural variations in Earth's rotation are to be expected, research indicates that human activities are also contributing to these changes. NASA researchers have found that movements of ice and groundwater associated with climate change have increased the length of our days by approximately 1.33 milliseconds per century between 2000 and 2018. Additionally, significant events, such as the 2011 earthquake in Japan, have been shown to affect Earth's spin, shortening the day by 1.8 microseconds.
Seasons also play a crucial role in influencing Earth's rotation. According to Richard Holme, a geophysicist at the University of Liverpool, the distribution of landmass differs between the northern and southern hemispheres. During the northern summer, the growth of leaves on trees shifts mass from ground level to higher elevations, thereby affecting the planet's spin axis. This redistribution of mass can lead to slight variations in the length of the day.
It's important to note that while the days are becoming shorter, our clocks will continue to register 24 hours. The changes are subtle and typically unnoticeable on an individual level. However, if the discrepancy in day length exceeds 0.9 seconds (or 900 milliseconds), it could affect time zones. Although such a significant shift has never occurred within a single day, over time, our clocks can become misaligned with Earth's actual rotation.
To address this issue, the International Earth Rotation and Reference Systems Service (IERS) monitors these variations and will implement leap seconds to Coordinated Universal Time (UTC) as necessary to ensure our clocks remain in sync with Earth's position. This careful balance helps maintain the accuracy of our timekeeping systems amidst the fluctuations in Earth's rotation.
