Earth is expected to spin more quickly in the coming weeks, making some of our days unusually short. On July 9, July 22 and Aug. 5, the position of the moon is expected to affect Earth’s rotation so that each day is between 1.3 and 1.51 milliseconds shorter than normal.
A day on Earth is the length of time needed for our planet to fully rotate on its axis — approximately 86,400 seconds, or 24 hours. But Earth’s rotation is affected by a number of things, including the positions of the sun and moon, changes to Earth’s magnetic field, and the balance of mass on the planet.
Since the relatively early days of our planet, Earth’s rotation has been slowing down, making our days longer. Researchers found that about 1 billion to 2 billion years ago, a day on Earth was only 19 hours long. This is likely because the moon was closer to our planet, making its gravitational pull stronger than it is now and causing Earth to spin faster on its axis.
Since then, as the moon has moved away from us, days on average have been getting longer. But in recent years, scientists have reported variations in Earth’s rotation. In 2020, scientists found that Earth was spinning more quickly than at any point since records began in the 1970s, and we saw the shortest-ever recorded day on July 5, 2024, which was 1.66 milliseconds shy of 24 hours, according to timeanddate.com.
On July 9, July 22 and Aug. 5, 2025, the moon will be at its furthest distance from Earth’s equator, which changes the impact its gravitational pull has on our planet’s axis. Think of the Earth as a spinning top — if you were to put your fingers around the middle and spin, it wouldn’t rotate as quickly as if you were to hold it from the top and bottom.
With the moon closer to the poles, the Earth’s spin speeds up, making our day shorter than usual.
Related: Have days on Earth always been 24 hours?
These variations are to be expected, but recent research suggests that human activity is also contributing to the change in the planet’s rotation. Researchers at NASA have calculated that the movement of ice and groundwater, linked to climate change, has increased the length of our days by 1.33 milliseconds per century between 2000 and 2018.
Single events can also affect Earth’s spin: the 2011 earthquake that struck Japan shortened the length of the day by 1.8 microseconds. Even the changing seasons affect Earth’s spin, Richard Holme, a geophysicist at the University of Liverpool, told Live Science via email.
“There is more land in the northern hemisphere than the south,” Holme said. “In northern summer, the trees get leaves, this means that mass is moved from the ground to above the ground — further away from the Earth’s spin axis.” The rate of rotation of any moving body is affected by its distribution of mass. When an ice skater spins on the spot, they rotate faster when their arms are tight to their chest, and slow themselves down by stretching their arms out. As Earth’s mass moves away from its core in summer, its rate of rotation must decrease, so the length of the day increases, Holme explained.
Of course, on the days in question our clocks will still count 24 hours. The difference isn’t noticeable on the individual level.
The only time we would see a change to time zones is if the difference between the length of day is greater than 0.9 seconds, or 900 milliseconds. Though this has never happened in a single day, over the years our clocks fall out of sync with the position of the planet. This is monitored by the International Earth Rotation and Reference Systems Service (IERS), which will add a “leap second” to UTC as needed to bring us back in line.