Researchers report that in the coming weeks Earth will rotate a bit faster, shortening the length of some days. July 9 was already a shorter day. The same is expected on July 22 and August 5, when days will be about 1.3 to 1.51 milliseconds shorter because of the Moon’s position relative to Earth.
A day on Earth lasts 24 hours, or 86,400 seconds. That’s how long it takes our planet to complete a full rotation on its axis. But that rotation is influenced by several factors, including the positions of the Sun and Moon, changes in Earth’s magnetic field, and the redistribution of mass on Earth’s surface.
Since Earth’s formation, its rotation has gradually slowed, lengthening days. Researchers estimate that 1 to 2 billion years ago a day on Earth lasted only about 19 hours. That’s likely because the Moon was closer then, which increased its gravitational pull and made Earth spin faster.
As the Moon has moved away, the average length of a day has increased. But in recent years scientists have observed changes in Earth’s rotation. In 2020 they recorded Earth spinning faster than at any time since systematic observations began in the 1970s.
On July 5, 2024, scientists recorded the shortest day in the history of observations. According to data from timeanddate.com, it was shorter by 1.66 milliseconds.
On July 22 and August 5, 2025, the Moon will reach its greatest distance from Earth’s equator, changing its gravitational influence on Earth’s rotation. (The same happened on July 9.)
Imagine Earth as a spinning top. If you hold it by the middle and spin it, it will rotate more slowly than if you hold it by the top and bottom.
As the Moon moves toward the poles, Earth’s rotation speeds up, making the day slightly shorter than usual.
Human Impact and Other Factors
These variations are expected. But recent studies show that human activity is also nudging Earth’s rotation. NASA calculated that melting ice and shifting groundwater linked to the climate crisis increased the length of our day by about 1.33 milliseconds per century between 2000 and 2018.
Earth’s rotation can also change because of sudden events. For example, the 2011 earthquake in Japan shortened the length of the day by 1.8 microseconds. Even seasonal shifts affect Earth’s rotation, Richard Holme, a geophysicist at the University of Liverpool, told Live Science.
“In the Northern Hemisphere there is more land than in the Southern Hemisphere. In the summer, trees in the north are covered with leaves, which means that mass is moving to the surface—further from the axis of Earth’s rotation,” Holme explained to Live Science. The rotation speed of any moving body depends on how its mass is distributed. As mass shifts farther from Earth’s rotation axis in summer, Earth’s rotation slows, producing slightly longer days, Holme said.
Of course, clocks will still read 24 hours and we won’t feel the difference. Holme said changing time zones would only be necessary if the day lengthened by about 900 milliseconds (0.9 seconds).
