Earth had the shortest day since the invention of the atomic clock

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

A spin is the amount of time it takes for the earth to rotate around its own axis once, which is approximately the case 84,600 seconds.

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

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

Although June 29 broke the record for the shortest day in modern history, Earth has had much shorter days, he said.

When dinosaurs roamed the planet 70 million years ago, a single day on Earth lasted about 23 1/2 hours, according to a 2020 study published in Paleoceanography and Paleoclimatology.
Since 1820, scientists have documented the slowing of the Earth’s rotation, according to NASA. In recent years, it has started to accelerate, McCarthy said.

Why is the speed increasing?

Researchers don’t have a definitive answer as to how or why the Earth is spinning slightly faster, but it could be due to the isostatic adjustment of glaciers or the land’s movement due to melting glaciers, McCarthy said.

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

As the poles melt due to the climate crisis, there’s less pressure on 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 increase and decrease their speed, he said.

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When skaters extend their arms away from their body while spinning, they need more strength to spin, he said. When they tuck their arms close to their body, their speed increases because their body mass is closer to their center of gravity, McCarthy said.

As the Earth gets rounder, its mass moves closer to its center, increasing its speed of rotation, he said.

Some have suggested a correlation with the Chandler wobble, McCarthy said. The axis on which our planet spins is not aligned with its axis of symmetry, an invisible vertical line dividing 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 while spinning because it often doesn’t rotate about the axis of symmetry, he said.

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

However, McCarthy said that the Chandler wobble is unlikely to affect Earth’s rotational speed because the wobble is due to the planet’s shape. As the planet’s shape changes, the frequency of the wobble changes, not its rotation frequency, he said.

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Remove a leap second

Ever since researchers began measuring Earth’s rotation speed with atomic clocks, the Earth’s rotation speed has slowed, McCarthy said.

“Our everyday lives don’t even know that millisecond,” McCarthy said. “But if these things add up, the rate at which we insert a leap second could change.”

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

Because the Earth is now spinning faster, a leap second would have to be taken away to catch up with our timekeeping as the Earth’s increasing spin speed, McCarthy said.

If the planet continues this rotation trend, the leap second would likely not have to be removed for another three to four years, he said.

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