Days Are Growing Shorter, What’s Happening?

In the summer, days are supposed to be longer, but recently, they have started to shorten. The U.S. Naval Observatory and the International Earth Rotation and Reference Systems Service study shows that on Friday, July 11, 2025, the day was 1.34 milliseconds short of reaching 24 hours.

One rotation of Earth is equivalent to one day. However, over the past decade, days have become increasingly shorter, with each day lasting under 24 hours. This might not seem normal, but it is. In the long term, days will grow longer. This is due to the Moon’s gravitational pull on Earth, which causes Earth to slow down. But days are not always gradually increasing in time. Sometimes, there is a period where days are shorter than 24 hours, such as in recent periods. Though it seems unusual, it is completely normal, typically only lasting a decade or so. According to the New York Times, “A Tyrannosaurus rex that lived 70 million years ago would have experienced an average daily rotation of about 23 1/2 hours.”

In the next 250 million years, days are expected to increase by 1.5 hours. Partially, this is due to the tidal acceleration of the Moon, which slows Earth down, and friction effects between the core and mantle. These factors increase the amount of energy Earth needs to rotate, ultimately slowing the Earth’s rotation and increasing the time it takes for each day.

Other than tidal acceleration and friction effects, Earth’s rotation is slowed down by human causes, such as climate change, pollution, etc. As the climate warms, glaciers can melt and spread to places near the Equator. After ice melts, the water spreads to different parts of the world, causing Earth to spin slower. Such as the New York Times had written, “[And] much like a spinning ice skate that rotates more slowly when his arms are spread out, and spins more quickly when he pulls his arms close,” where the ice skater is Earth and his hands is the melted water.

In closing, days on Earth are not consistent. Sometimes the day might end a little before 24 hours, but sometimes it might last over 24 hours. But as time progresses, days will gradually lengthen, and who knows, maybe there will be a time when each day has 30, 40, or even 50 hours.

Sources:

https://en.wikipedia.org/wiki/Future_of_Earth

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