Earth Spins Faster: Aug. 5 Joins Summer’s Record-Short Days

Long before atomic clocks, humans relied on the sun, water, and even incense to track time.

Published: 8/5/2025, 4:24:13 PM EDT

Earth Spins Faster: Aug. 5 Joins Summer’s Record-Short Days — This photo provided by Firefly Aerospace shows Firefly’s Blue Ghost lunar lander captures the Blue Marble while in Earth orbit on Jan. 23, 2025. (Firefly Aerospace via AP)

The Earth seems to be moving just a little faster than before, and it has scientists debating leap seconds and tracking millisecond variations. Aug. 5 is the third day this summer that’s expected to be one of the shortest days known, according to the International Earth Rotation and Reference Systems Service and Timeanddate.com.

Earth has already logged two record-short days in 2025: July 9 and July 22. The planet spun more than a millisecond faster than the standard 86,400-second, or 24-hour day. Today’s rotation is projected to end about 1.51 milliseconds early.

While a millisecond is just 0.001 seconds and shorter than a blink of an eye, the implications are significant. Precise timekeeping underpins everything from GPS and satellite communications to financial markets. Even a discrepancy of a single millisecond can lead to positioning errors of several meters.

Earth’s spin has gradually slowed over millions of years, but since 2020 it has unexpectedly sped up. The U.S. Naval Observatory (USNO) reports that the length of day is now shorter by about 1.5 milliseconds, the briefest since the late 19th century. Past variations have ranged from 6 milliseconds shorter in 1660 to 4 milliseconds longer in 1910.

This acceleration has led to a historic possibility: a “negative leap second.” Leap seconds are adjustments to Coordinated Universal Time (UTC) that keep atomic clocks in line with the planet’s rotation.

Historically, leap seconds are added to account for Earth’s gradual slowdown, but if the planet keeps spinning faster, a second may need to be subtracted. This would be a first in history, according to the USNO and the National Institute of Standards and Technology.

Timeanddate.com explains that Earth is an “almost-but-not-quite-perfect timekeeper.” Tiny fluctuations in rotation, also known as the length of day (LOD), can only be measured using atomic clocks. Until 2020, the shortest LOD ever recorded was minus 1.05 milliseconds. Since then, Earth has repeatedly broken that record, reaching minus 1.66 milliseconds on July 5, 2024.

Long before atomic clocks, humans relied on the sun, water, and even incense to track time. For example, ancient Chinese civilizations pioneered water clocks, sundials, and incense clocks to mark the rhythm of the day, reflecting a deep connection to nature and astronomy, according to a review from The Epoch Times on timekeeping methods of ancient China. A Tang Dynasty poem states, “One inch of time is worth an inch of gold,” a reminder of the value of time. One ancient tool for timekeeping was called the gnomon, and it captured this concept by using a vertical pole and horizontal ruler to track the sun’s moving shadow.