August 5, 2025, will be one of the shortest days in history. Meanwhile, scientists are at a loss as to the reasons for the mysterious acceleration of the Earth.

Earth. Source: NASA

The period of the Earth’s rotation around its axis (one full rotation of 360 degrees relative to the stars) lasts 23 hours, 56 minutes, and 4.1 seconds. This is known as a sidereal day. It explains why stars and planets rise in the east about four minutes earlier each day, and why the night sky changes depending on the season. After all, the Earth moves in its orbit around the Sun while simultaneously rotating around its axis.

But the fact is that we live according to the solar day, not the sidereal day. It is measured from noon to noon and lasts exactly 24 hours (86,400 seconds). Since official records began in 1973, the length of daylight has steadily increased, mainly due to the Moon. As it moves around the Earth, it creates friction, causing its orbit to shift further away from our planet. At the same time, the Earth’s rotational energy is transferred to the Moon, which leads to a slowdown in the Earth’s rotation and, consequently, to an increase in the length of days.

However, this situation has changed in recent years. After decades of slowing down, our planet’s rotation has accelerated — and researchers cannot provide a clear explanation for why. In 2025, they predicted three dates when the solar day on Earth would be shorter than 24 hours: July 9 (1.23 milliseconds shorter than 24 hours), July 22 (1.36 milliseconds shorter), and August 5 (1.25 milliseconds shorter). The title of the shortest day in history is currently held by July 5, 2024. On that day, the day was 1.66 milliseconds shorter than 24 hours.

A difference of just 1.25 milliseconds from the 86,400-second mark may seem insignificant, but it is indicative of global processes that we are not yet able to understand. According to one theory, global warming is to blame. On the other hand, the acceleration is caused by the slowing down of the liquid part of the Earth’s core, as a result of which the rest of the planet rotates faster.

Regardless of the reasons for the acceleration, according to scientists, if the current trend continues until 2029, then, for the first time in history, a so-called negative leap second may be added to compensate for the deviation.

According to Space.com