The Earth broke the record for the shortest day since atomic clocks were invented

Earth completed its normal 24-hour rotation 1.59 milliseconds fast on June 29, breaking the record for the shortest day in modern history.
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Earth completed its normal 24-hour rotation 1.59 milliseconds fast on June 29, breaking the record for the shortest day in modern history. (POT)

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ATLANTA — If you feel like there’s less time in the day, you’re right.

Scientists recorded the shortest day on Earth since the invention of the atomic clock.

Our planet’s rotation was measured to be 1.59 milliseconds less than the normal 24-hour day on June 29, according to the International Earth Rotation and Reference Systems Servicean organization in charge of global timekeeping.

One rotation is the time it takes for the Earth to rotate once on its axis, which is approximately 86,400 seconds.

The previous record was set on July 19, 2020, when the day measured 1.47 milliseconds less than normal.

The atomic clock is a standardized unit of measurement that has been used since the 1950s to tell time and measure the Earth’s rotation, said Dennis McCarthy, retired director of time at the US Naval Observatory.

Even though June 29 broke the record for the shortest day in modern history, there have been much shorter days on Earth, he said.

When dinosaurs still roamed the planet 70 million years ago, a single day on Earth lasted about 23½ hours, according to a 2020 study published in Paleoceanography and Paleoclimatology.

Since 1820, scientists have documented the slowing down of the Earth’s rotation, according to nasa. In recent years, it has started to accelerate, McCarthy said.

Why does the speed increase?

Researchers don’t have a definitive answer as to how or why Earth is spinning a little faster, but it may be due to isostatic adjustment by glaciers or the movement of the earth due to glacial melt, McCarthy said.

Earth is slightly wider than it is tall, making it an oblate spheroid, he said. Glaciers at the poles weigh down on Earth’s crust at the north and south poles, McCarthy said.

Since the poles are melting due to the climate crisis, there is less pressure at the top and bottom of the planet, which moves the crust up and makes the Earth rounder, he said. The circular shape helps the planet spin faster, McCarthy said.

It’s the same phenomenon that figure skaters use to speed up and slow down, he said.

When skaters stretch their arms away from the body as they spin, they need more force to rotate, he said. When they bring their arms close to their body, their speed increases because their body mass is closer to their center of gravity, McCarthy said.

As Earth gets rounder, its mass gets closer to its center, which increases its rotation speed, he said.

Our everyday existence does not even recognize that millisecond.

-Dennis McCarthy, retired weather director at the US Naval Observatory

Some have suggested a correlation with the Chandler wobble, McCarthy said. The axis on which our planet rotates is not aligned with its axis of symmetry, an invisible vertical line that divides the Earth into two equal halves.

This creates a slight wobble as the Earth rotates, similar to how a soccer ball wobbles when thrown, he said.

When a player throws a soccer ball, it wobbles slightly as it spins because it often doesn’t rotate around the axis of symmetry, he said.

“If you’re really a good passer in football, you align the axis of rotation with the axis of symmetry of the ball and it doesn’t wobble,” McCarthy said.

However, McCarthy said that the Chandler wobble probably doesn’t affect Earth’s rotation rate because the wobble is due to the shape of the planet. If the shape of the planet changes, the wobble frequency changes, not its rotation frequency, she said.

remove a leap second

Ever since researchers began measuring Earth’s rotation rate using atomic clocks, Earth has been slowing down in rotation, McCarthy said.

“Our everyday existence doesn’t even recognize that millisecond,” McCarthy said. “But if these things add up, then it could change the speed at which we insert a leap second.”

In cases where milliseconds add up over time, the scientific community has added a leap second to the clock to slow down our time to match Earth’s, he said. 27 leap seconds have been added since 1972, according to EarthSky.

Because Earth is now spinning faster, a leap second would need to be removed to bring our timing up to date with Earth’s increasing rotational speed, McCarthy said.

If the planet continues this rotational trend, the removal of a leap second probably won’t have to happen for another three or four years, he said.

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