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

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 time director at the US 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.

Why does the speed increase?

McCarthy said researchers don’t have a definitive answer as to how or why the Earth is spinning a little faster, but it could be due to glacial equilibrium adaptation, or the movement of the Earth due to melting glaciers.

He said that the Earth is a little wider than its height, making it an oblate spheroid. McCarthy said that polar glaciers weigh heavily on the Earth’s crust at the North and South Poles.

He said that because the poles are melting due to the climate crisis, there is less pressure on the top and bottom of the planet, moving the crust up 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 rotate, it takes more force for them to rotate, he said. When they place their arms close to their body, McCarthy said, their speed increases because their body mass is closer to their center of gravity.

He said that when the Earth becomes round, its mass becomes closer to its center, which increases the speed of its rotation.

McCarthy said that some have suggested a relationship with Bob Chandler. The axis on which our planet rotates does not line up with the axis of symmetry, an invisible vertical line that divides the Earth into two equal halves.

This creates a slight wobble with the rotation of the earth, he said, similar to how a soccer ball vibrates when thrown.

He said that when a soccer player is tossed, it sways slightly as it spins because it doesn’t often rotate around the axis of symmetry.

“If you are a really good passer in soccer, you line up the rotation axis with the soccer symmetry axis, McCarthy said.

However, McCarthy said that Chandler’s oscillation likely does not affect the speed of Earth’s rotation because the oscillation is due to the shape of the planet. If the planet’s shape changes, he said, it changes the frequency of its oscillation, not its rotation frequency.

Removing the leap second

Since researchers began measuring the Earth’s rotation speed using atomic clocks, McCarthy said, the Earth has been slowing down its rotation speed.

“Our daily existence doesn’t even acknowledge the millisecond,” McCarthy said. “But if these things combine, it can change the rate at which we enter a leap second.”

Because the Earth is now spinning faster, McCarthy said, a leap second must be taken away to catch up on our timekeeping with the Earth’s increasing rotational speed.

If the planet continues in this rotational trend, he said, a leap second removal likely won’t occur for another three to four years.