Scientists have recorded the shortest day on Earth since the invention of the atomic clock.
Rotation is the time it takes the Earth to rotate once on its axis, which is approximately 86400 sec.
The previous record was documented on July 19, 2020, when the day’s measurement was 1.47 milliseconds shorter than normal.
The atomic clock is a standard unit of measurement that has been used since the 1950s to determine time and measure the Earth’s rotation, said Dennis McCarthy, retired director of time at the US Naval Observatory.
While June 29 broke the record for the shortest day in modern history, there have been much shorter days on Earth, he said.
Why does the speed increase?
McCarthy said the researchers don’t have a definitive answer as to how or why the Earth is rotating a little faster, but it could be due to glacial balance adaptation or the Earth’s movement due to melting glaciers.
He said that the Earth is slightly wider than its height, making it an oblate spheroid. McCarthy said polar glaciers weigh heavily on the Earth’s crust at the north and south poles.
He said that as the poles are melting due to the climate crisis, there is less pressure on the top and bottom of the planet, moving the crust upwards and making the Earth round. The circular shape helps the planet spin faster, McCarthy said.
It’s the same phenomenon that snowboarders use to increase and decrease their speed, he said.
When skaters extend their arms away from their bodies as they spin, it takes more force to spin, he said. When they put their arms close to their bodies, McCarthy said, their speed increases because their body mass is closer to the center of gravity.
He said that when the Earth becomes round, its mass gets closer to its center, which increases the speed of its rotation.
McCarthy said some have suggested a relationship with Bob Chandler. The axis on which our planet rotates does not align with the axis of symmetry, an invisible vertical line that divides the Earth into two equal halves.
This creates a slight wobble with the earth’s rotation, he said, similar to the way a football vibrates when thrown.
He said that when a football player is pitched, he sways slightly as he spins, because he doesn’t usually rotate around the axis of symmetry.
“If you are a good passer in football, align the axis of rotation with the axis of symmetry in football, McCarthy said.
However, McCarthy said the Chandler wobble probably doesn’t affect Earth’s rotation speed because the wobble is due to the planet’s shape. If the planet’s shape changes, he said, the frequency of its oscillation changes, not its frequency of rotation.
Removing the leap second
Ever since researchers began measuring the Earth’s rotational speed using atomic clocks, McCarthy said, the Earth has been slowing down.
“Our daily existence doesn’t even recognize the millisecond,” McCarthy said. “But if those things combine, it could change the rate at which we enter a leap second.”
Because the Earth is now rotating faster, McCarthy said, a leap second must be taken to keep up with our timing as the Earth’s rotation speed increases.
If the planet continues on this rotational trend, he said, a leap second removal is unlikely to occur for another three to four years.
revision: An earlier version of this story gave the incorrect number of seconds for the Earth to take once on its axis.
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