One of the Shortest Days in History!

Written by: Keya Gambhir

Yesterday, July 22, Earth finished its daily spin in a little less time than normal. Scientists measured the day as 1.34 milliseconds shorter than the usual 24 hours. Even though this difference is very tiny and much shorter than a blink of an eye, it is one of the shortest days ever recorded since precise timekeeping began.

This short day is part of a surprising trend. Earth has been spinning faster in recent years instead of slowing down like it usually does. Earlier this month, July 9 and July 10 were also very short days with Earth spinning 1.23 and 1.36 milliseconds faster than normal. Another short day is expected on August 5 when Earth might spin 1.25 milliseconds faster.

Earth’s spinning is never exactly the same. For billions of years, Earth has been gradually slowing down. This is mostly because of the Moon. The Moon’s gravity pulls on Earth’s oceans and surface creating tides. This pull acts like a brake that slowly makes Earth spin more slowly. In fact, Earth’s day has gotten longer by about 1.8 milliseconds every 100 years because the Moon is moving farther away.

But since 2020, Earth has been spinning faster. Scientists are still trying to understand why this change is happening. Some think it has to do with where the Moon is in its orbit. When the Moon is closer to the equator, its pull slows Earth’s spin. When it moves closer to the poles, Earth spins a little faster. This summer, the Moon has been closer to the poles which may explain some of the faster spinning.

The air around Earth also affects how the planet spins. During summer, the jet stream slows down. Because the atmosphere spins more slowly, Earth must spin a little faster to keep the total movement balanced.

Something strange is also happening inside Earth. The planet’s liquid core has been slowing down for many years. To keep the spinning balanced, the solid part of Earth above the core has been spinning faster. Scientists do not yet know why the core is slowing down or what might happen next.

Long ago, Earth’s days were much shorter. Fossils show that about 70 million years ago days lasted about 23.5 hours. Even further back about 430 million years ago days were closer to 21 hours long. Over a very long time, Earth has been slowing down, but these recent faster days are unusual.

Most people will not notice these small changes. A blink takes about 100 to 400 milliseconds which is much longer than the tiny change in Earth’s spin. But these small differences are very important for things like GPS satellites and even the internet. These systems rely on very exact time.

To keep time accurate, scientists sometimes add a leap second to the clock to catch up with Earth’s slower spin. Since 1972, 27 leap seconds have been added. But if Earth keeps spinning faster, a leap second might need to be removed in the future. This would be the first time something called a negative leap second happens. Some experts worry this could cause problems for computers and software that expect time to always move forward.

Climate change may also be affecting Earth’s rotation. Melting glaciers, rising sea levels and shifting water underground can change how Earth’s mass is spread out. This can slow the spin a little. One study showed that climate change has made days longer by about 0.6 to 0.7 milliseconds in the last century. This slowing effect may now be competing with forces that make Earth spin faster.

Because of all these factors, scientists find it hard to predict exactly how long a day will be in the future. The planet’s spin changes in ways that are not fully understood. What we do know is that Earth’s rotation is always changing even if by tiny amounts.

So even though July 22 was one of the shortest days in history, the sun still rose and set as usual. The spin of our planet may be speeding up a little for now but it is part of a complex dance that will keep scientists watching closely in the years to come.