A revolution is the amount of time it takes the Earth to rotate once on its axis, which is about 84,600 seconds.
The previous record was established on July 19, 2020, when the day was 1.47 milliseconds shorter than normal.
The atomic clock is a standardized unit of measurement that has been used since the 1950s to tell time and measure Earth’s rotation, said Dennis McCarthy, retired director of time at the U.S. Naval Observatory.
Although June 29 broke a 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 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 Earth’s rotation, according to NASA. In recent years it has started to accelerate, McCarthy said.
Why is the speed increased?
Researchers don’t have a definitive answer as to how or why the Earth spins slightly faster, but it could be due to isostatic adjustment of glaciers or land movement due to melting glaciers, McCarthy said.
The Earth is slightly wider than it is tall, which makes it a spheroid, he said. Glaciers at the poles weigh down the Earth’s crust at the North and South poles, McCarthy said.
As the poles melt 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 figure skaters 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 clench their arms close to their bodies, their speed increases because their body mass is closer to their center of gravity, McCarthy said.
As the Earth becomes rounder, its mass moves closer to its center, which increases its rotation speed, he said.
Some have suggested a correlation with Chandler’s swing, McCarthy said. The axis on which our planet spins 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 football wobbles when it is thrown, he said.
When a player throws a football, it wobbles slightly as it spins, as it often doesn’t rotate around the axis of symmetry, he said.
“If you’re a really good passer of the 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 Chandler’s 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, the frequency of the oscillation changes, not the frequency of its rotation, he said.
Remove a leap second
Since researchers began measuring Earth’s rotation speed using atomic clocks, Earth has slowed its rotation speed, McCarthy said. “Our day-to-day existence doesn’t even recognize that millisecond,” McCarthy said. “But if these things add up, then it could change the rate at which we introduce a leap second.” In cases where milliseconds accumulate over time, the scientific community has added a leap second to the clock to slow our time down to match Earth time, he said. 27 leap seconds have been added since 1972, according to EarthSky. Because the Earth is now spinning faster, a leap second would have to be removed to accommodate our timing with the Earth’s increasing rotational speed, McCarthy said. If the planet continues this rotational trend, removing a leap second probably won’t need to happen for another three to four years, he said.
