World Spins Faster: Will Days Get Shorter?
Earth’s rotation is speeding up, leading to slightly shorter days this summer, though the change is imperceptible to humans.
Key Development
During July and August, the world will rotate faster, with certain days, like July 9 and 22 and August 5, being approximately 1.3 to 1.51 milliseconds shorter than usual. This change is primarily attributed to the moon’s gravitational pull, according to Livescience. This gravitational force affects the Earth’s rotation as the moon’s position relative to Earth’s center changes.
This is just a simulation, but it really does show how the Moon is tidally locked to the Earth.
The same side of the Moon always faces the Earth.
Very cool!
[source: NASA Ames]
“The rotation of the world depends on where the mass is. If the mass is near the rotation the world will rotate faster. But if the mass is spreading far the speed will decrease.”
—Expert, Unspecified Title
Context sentence citing a new statistic (Source 2025) …
Interestingly, the Earth’s core may also be experiencing changes. According to a study published in Nature Geoscience, the Earth’s inner core’s rotation has slowed since 2010.
Background
The world has spun at varying speeds throughout its history; 1 to 2 billion years ago, a day lasted only 19 hours due to the moon’s proximity. The moon has gradually moved away, slowing the Earth’s rotation over time. However, recent years have shown unexpected changes. In 2020, the Earth’s rotation was the fastest since the 1970s. July 5, 2024, saw the fastest rotation, shortening the day by 1.66 milliseconds.
The earth from space.
Factors Influencing Rotation
Apart from lunar gravity, other factors influence Earth’s rotation. Variations in the Earth’s magnetic field and weight distribution, such as ice melt, affect the planet’s spin. NASA found that water and ice movement from 2000 to 2018, influenced by global warming, altered rotation by 1.33 milliseconds per century. Major earthquakes, like the 2011 Japan event, also caused a reduction of 1.8 microseconds. Seasonal changes, such as the increased foliage in the Northern Hemisphere during summer, shift weight away from the Earth’s axis, slowing it down.
Impact and Adjustments
Humans do not perceive these millisecond changes, as clocks still measure 24 hours per day. Noticeable effects would only occur with discrepancies exceeding 0.9 seconds, which has never happened in a single day. Over time, these small changes accumulate, causing a mismatch between clock time and Earth’s actual rotation. To address this, the International Earth Rotation and Reference Systems Service (IERS) occasionally adds a “leap second” to UTC time to maintain accuracy.
Final outlook paragraph …
While imperceptible to daily life, this accelerated rotation is monitored by scientists because it has consequences for the climate, gravity, and other human activity.
