WASHINGTON — Wednesday will be slightly shorter than usual thanks to our planet’s 

Earth is expected to complete a full rotation on July 9 in roughly 1.30 milliseconds less than the standard 86,400 seconds that define a 24-hour day, according to predictions based on astronomical observations.

While that tiny time difference is imperceptible to humans, it represents part of a broader pattern that has left scientists scratching their heads: after thousands of years of slowing down, Earth has been spinning faster in recent years, consistently breaking records for its shortest days.

Until 2020, the shortest day ever recorded by atomic clocks was 1.05 milliseconds under the standard length. Since then, Earth has broken that record every year by roughly half a millisecond. The shortest day on record was July 5, 2024, when Earth completed its rotation 1.66 milliseconds faster than normal.

The phenomenon can only be measured using atomic clocks, which are precise enough to detect variations of thousandths of a second. A millisecond equals 0.001 seconds.

Scientists measure these tiny daily variations as “length of day,” or LOD, representing how many milliseconds above or below 86,400 seconds Earth takes to complete one rotation relative to the sun.

The moon’s position influences these short-term variations. Earth spins faster when the moon is positioned far north or south of the planet’s equator. Two other upcoming dates this year, July 22 and August 5, are also expected to produce similarly brief days, with August 5 expected to be the shortest, losing 1.51 milliseconds. 

Long-term changes in the planet’s spin speed largely stem from Earth’s core acting in unpredictable ways, researchers say. 

The acceleration trend may be reaching its peak. Leonid Zotov, an expert in Earth rotation at Moscow State University, predicted last year that Earth would begin decelerating, though that hasn’t happened yet.

“I think we have reached the minimum,” he told TimeandDate.com. “Sooner or later, Earth will decelerate.”