Scientists don't know why Earth's days are mysteriously lengthening

As astronomical observations and atomic clocks have combined, astronomical observations have revealed that the length of a day is suddenly increasing. The reason for this is unknown to scientists.

As a result, things like GPS and other precision technologies that govern our modern lives will be affected not just in terms of timekeeping, but also in terms of our ability to use them.

The Earth's rotation has accelerated over the past few decades. This trend has been making our days shorter since it determines how long a day is. A record was set in June 2022 for the shortest day in more than half a century.

While this record is impressive since 2020 there has been an apparent slowdown in the steady speedup. There has been a noticeable increase in the number of days, and so far no explanation has been found for why.

While our phones indicate there are exactly 24 hours in a day, Earth's rotation time can differ ever so slightly from our clocks. The changes may occur over millions of years, or they may occur almost instantly. The effects of earthquakes and storms, for instance, can be significant.

A frictional effect associated with the Moon's tides has caused Earth's rotation to slow over millions of years. Each day is lengthened by about 2.3 milliseconds every 100 years due to this process. An Earth day was only about 19 hours long a few billion years ago.

The Earth has rotated faster over the past 20,000 years due to another process working in the opposite direction. After the last ice age ended, melting polar ice sheets reduced surface pressure, allowing Earth's mantle to move steadily towards the poles.

The speed at which our planet spins increases as this mass of mantle moves closer to Earth's axis, just as a ballet dancer spins faster when their arms move toward their body. Every century, this process has shortened by about 0.6 milliseconds.

The connection between Earth's interior and the surface becomes more important over time. A major earthquake can change the length of the day, although by a small amount. In 2011, the Great Tohoku Earthquake in Japan sped up Earth's rotation by 1.8 microseconds, according to scientists.

The weather and climate have also significant impacts on the rotation of Earth over shorter periods, causing variations in both directions. As mass moves around the planet on a fortnightly and monthly basis, the length of the day can be changed by up to a millisecond. 

A length-of-day record that spans 18.6 years shows tidal variations. Ocean currents and the movement of our atmosphere also play a role. In addition, seasonal snow cover and rainfall, or groundwater extraction, affect things further.