Scientists recorded the shortest day on Earth since the invention of the atomic clock.
One rotation is the time it takes the Earth to rotate once on its axis, which is approximately 84,600 seconds.
The previous record was documented on July 19, 2020, when the day measured 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 weather at the U.S. Naval Observatory.
Although 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 23 1/2 hours, according to a 2020 study published in Paleoceanography and Paleoclimatology. Since 1820, scientists have documented that Earth’s rotation slowed, according to NASA. In recent years, it began to accelerate, McCarthy said.
Why does the speed increase?
Researchers don’t have a definitive answer as to how or why the Earth spins a little faster, but it may be due to glacial isostatic adjustment or land movement due to melting glaciers, McCarthy said.
The Earth is slightly wider than it is tall, making it an oblate spheroid, he said. Glaciers at the poles weigh on the Earth’s crust at the north and south poles, McCarthy said.
As 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 increase and decrease their speed, he said.
When skaters pull their arms away from their body as they spin, they need more force to spin, he said. When they bring their arms closer 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 hesitation, 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 spins, similar to how a soccer ball moves when it is thrown, he said.
When a player throws a ball, it wobbles slightly as it spins because it often doesn’t spin around the axis of symmetry, he said.
“If you’re a good passer in 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 rate because the wobble is due to the planet’s shape. If the planet’s shape changes, the wobble frequency changes, not its rotation frequency, he said.
Removal of an interleaved second
Ever since researchers began measuring Earth’s rotation speed using atomic clocks, Earth had been slowing its rotation speed, McCarthy said.
“Our daily existence doesn’t even recognize that millisecond,” McCarthy said. “But if these things add up, then it could change the rate at which we insert a split 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 the Earth is now spinning faster, a leap second would need to be removed in order to catch up with our timing with the increased speed of the Earth’s rotation, McCarthy said.
If the planet continues this rotation trend, the elimination of an interleaved second probably shouldn’t happen for another three to four years, he said.