Why is the Earth spinning faster? Shortest day ever recorded

June 29 was 1.59 milliseconds short of 24 hours due to a strange speed-up of Earth’s rotation.
AP
Lowenna Waters4 August 2022

On June 29, Earth recorded its shortest day ever, when it completed a whole turn on its axis at 1.59 milliseconds short of 24 hours. We also recorded another shortened day on July 26, Popular Mechanics reported.

On both of these days, Earth completed its usual 24-hour rotation in less than 24 hours, and June 29 was the fastest time since atomic clocks began, tracking the planet’s rotation in the 1960s, according to timeanddate.com.

July 26 neared the newly-set record, at 1.50 milliseconds shorter than usual.

The new record offers proof that Earth is rotating faster in recent years. But why is this happening?

Here’s everything we know.

Why is the Earth spinning faster in recent years?

The Earth has broken its own speed record more than two dozen times since 2020, reversing an earlier decades-long run of slightly longer days.

The time taken by our planet to complete one spin about its axis with respect to “fixed stars” is 23 hours 56 minutes and 4.091 seconds. This day is known as the sidereal day.

However, Earth’s clocks and calendars are not based on the so-called sidereal day, because the Sun is closer to us. When people say there are 24 hours in a day, they mean a solar day, the time the Earth takes to complete one rotation so that the Sun then appears in the same position in the sky.

Scientists aren’t completely sure what’s causing the faster rotations, but there are some theories:

  • Changes to the climate or climate systems, which could cause the freezing of glaciers or excessive winds, whose shifting weight pulls on the Earth.
  • Earthquakes and other seismic activity move mass toward the centre of the Earth.
  • Movement within the Earth’s molten core that shifts mass on the planet.
  • Ocean circulation and pressure on the seabed that pulls on the Earth’s axis.
  • The “Chandler Wobble”, which is a natural shifting of the Earth’s axis due to it not being perfectly spherical, and is also connected to the fluctuations of Earth’s geographical poles.

Matt King, a professor at the University of Tasmania who specialises in Earth observation, told the Australian Broadcasting Corporation: “It’s certainly odd.

He added: “Clearly something has changed, and changed in a way we haven’t seen since the beginning of precise radio astronomy in the 1970s.”

If Earth continues to have shorter days, scientists may eventually have to subtract a second from atomic clocks, which would be the first example of a negative leap second in history.

Leap seconds have been added in the past to correct clocks, but nobody has had to cut them down so far.

Earth’s interactions with the Moon are also slowing it down, with previous studies showing that a day will be a minute longer in about 6.7 million years.

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