Recently, scientists have discovered that the Earth's rotation is accelerating, causing our days to become shorter. According to reports, on August 5, 2025, the earth will complete one rotation 1.33 milliseconds earlier than the standard 24-hour clock - the length of the day will be 86399.99867 seconds. This change is so subtle that ordinary people cannot detect it, but it can be accurately measured with modern high-precision instruments.
The Earth's true rotation period is called a "sidereal day", which is the time it takes for the Earth to rotate once relative to a distant star, which is 23 hours, 56 minutes, 4 seconds and 90.5 milliseconds. The "solar day" we use daily is slightly longer, about four minutes, because after every 360-degree rotation of the earth, it needs to rotate a little longer for the sun to return to the same position in the sky.
On August 5 this year, both the sidereal and solar days were slightly shorter than usual. Scientists pointed out that the causes of this phenomenon are complex and diverse, including atmospheric winds, ocean currents, the movement of molten material inside the Earth, and the gravitational effect of the moon.
Since the 1970s, scientists have used atomic clocks and astronomical observations to monitor deviations in the Earth's rotation. For example, in 1973, the Earth's annual cumulative rotation slowed down by +1106 milliseconds. For this reason, humans introduced "leap seconds" to ensure that the world's standard time is aligned with the Earth's rotation.
Even tiny differences can have a huge impact on precision systems such as the Global Navigation Satellite System (GPS). A deviation of 1.33 milliseconds results in a positioning error of about 62 centimeters in the equatorial region. If no correction is made, the cumulative one-year delay in 1973 alone will expand to about half a kilometer.
To achieve such precise measurements, scientists use quasars (extremely bright objects from billions of light-years away) as cosmic beacons. Quasars are nearly motionless and serve as perfect targets. Scientists use radio telescopes to observe the Earth's position against the background of these quasars, achieving sub-millisecond measurement accuracy.
The measured data is fed into a computer model that takes into account various influences from the atmosphere, ocean currents, and celestial bodies to predict the length of each day. In the short term, atmospheric wind speed is the biggest influencing factor. The interaction of wind with the Earth's surface can slow the Earth's rotation. In the Northern Hemisphere, wind speeds are fastest in winter and slowest in summer, so the length of the Earth day is the shortest from June to August each year.
In the long term, the melting of the Arctic and Antarctic glaciers shifts the distribution of Earth's mass toward the equator, slowing down its rotation like a figure skater stretching his arms. Geological events such as earthquakes also move geological mass, which affects rotation.
The tidal effects of the moon's gravity have slowly slowed the Earth's rotation over hundreds of millions of years. The tidal bulge is dragged in front of the moon's orbit, and the moon's gravity pulls it back, causing the earth's rotational energy to gradually transfer to the moon, causing it to move 3.8 centimeters away from the earth every year.
From 1973 to 2020, the Earth's rotation continued to slow down, and a total of 27 leap seconds were added around the world. But since 2020, the Earth has rotated slightly faster, which may be related to the interaction between the Earth's core and mantle.
July 5, July 22, and August 5, 2025, are predicted by scientists to be the three days of fastest rotation in the whole year. This phenomenon is the result of the combined forces of the Earth's internal dynamics, seasonal wind speeds, and the moon's weakened tidal drag.
Although ordinary people cannot detect these differences directly, "to precision atomic clocks and astronomical measurements based on quasars, everything is clear."