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One day on Earth could last 25 hours
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Bright orange sun setting over the Pacific Ocean at Long Beach, Pacific Rim National Park, with its reflection on the water and beach in British Columbia, Canada.
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Bright orange sun setting over the Pacific Ocean at Long Beach, Pacific Rim National Park, with its reflection on the water and beach in British Columbia, Canada.
Sunset over Pacific Ocean A sunset over the Pacific Ocean at Long Beach, British Columbia, Canada. With the slowing down of Earth's rotation caused by the tides, the day will be 25 hours in about 156 million years.

One day on Earth could last 25 hours

Written by
Erik Gregersen
Erik Gregersen is a senior editor at Encyclopaedia Britannica, specializing in the physical sciences and technology. Before joining Britannica in 2007, he worked at the University of Chicago Press on the...
Erik Gregersen
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Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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Wait, when is this? Is this going to happen any time soon? No, you’re not going to experience a weird “jet lag” anytime soon from a 25-hour day. However, the length of Earth’s day is increasing at the rate of 2.3 milliseconds per day per century. That is, Earth will have a 25-hour day about 156 million years from now.

This increase in the length of the day is caused by the tides slowing down Earth’s rotation. Earth’s oceanic tidal bulge is not directly in line with the Moon and is slightly ahead of the Moon. This misalignment causes a torque that slows down Earth’s rotation as the tidal bulge causes friction when it moves across Earth’s crust.

Geologists have observed this slowdown over Earth’s long history. About 1.4 billion years ago, the day was a mere 18.7 hours long. Some 600 million years ago, the day increased to 21 hours long. Within the last 100 million years, the day slowed to 24 hours.

Erik Gregersen