Earth’s daily rhythm is shifting quite literally. In the coming weeks, our planet will rotate ever so slightly faster, trimming a few milliseconds off our standard 24-hour day. On specific dates — July 9, July 22, and August 5, 2025 — changes in the moon’s position will briefly accelerate Earth’s spin, making each of these days about 1.3 to 1.51 milliseconds shorter than usual.
A single day is typically defined by one full rotation of Earth on its axis, clocking in at roughly 86,400 seconds (or 24 hours). However, this isn’t a fixed number. Earth’s spin is a delicate dance, influenced by gravitational nudges from the sun and moon, shifts in Earth’s magnetic field, and the distribution of mass across the globe, including ice, water, and even seasonal vegetation.
Historically, Earth has been slowing down. Around 1 to 2 billion years ago, our planet rotated much faster, with days lasting just 19 hours. Back then, the moon was much closer, exerting a stronger gravitational pull and increasing Earth’s spin. But as the moon slowly drifts away, Earth’s rotation has been easing up, stretching out the length of each day.
That said, recent observations tell a different story. In 2020, Earth was found to be spinning faster than at any time since measurements began in the 1970s. On July 5, 2024, we experienced the shortest recorded day, falling 1.66 milliseconds short of the usual 24 hours, according to timeanddate.com.
This year, on the dates in July and August, the moon will be at its farthest distance from Earth’s equator, altering the gravitational effect on our planet’s rotation. Imagine spinning a top: spinning it while holding the middle produces a slower rotation than gripping it from the top and bottom. Similarly, when the moon’s gravitational pull shifts closer to the poles, Earth spins faster.
Not all changes in Earth’s spin are cosmic. NASA researchers have linked shifts in groundwater and ice movement—especially those caused by climate change—to lengthened days. Between 2000 and 2018, this redistribution of mass slowed Earth’s rotation by 1.33 milliseconds per century.
Even massive natural events have a measurable effect. The 2011 earthquake in Japan, for example, shaved off 1.8 microseconds from a single day.
Seasonal changes also subtly influence the spin. As Richard Holme, a geophysicist at the University of Liverpool, explains,
“There is more land in the northern hemisphere than in the southern hemisphere. 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.”
Holme likens this to an ice skater spinning: “They rotate faster when their arms are tight to their chest, and slow themselves down by stretching their arms out.”
Similarly, when Earth’s mass is redistributed outward during summer, the planet spins more slowly and days grow incrementally longer.
Despite these shifts, we won’t notice any change in our daily lives. Our clocks will still run on the conventional 24-hour cycle. To truly affect our timekeeping systems, a day would need to differ by more than 0.9 seconds (900 milliseconds), a threshold we’ve never crossed in a single day.
To stay in sync with Earth’s natural rhythm, the International Earth Rotation and Reference Systems Service (IERS) sometimes inserts a “leap second” into Coordinated Universal Time (UTC). This ensures that our time remains aligned with the planet’s actual rotation.
