Skip to playerSkip to main contentSkip to footer
  • 4/19/2025
Thanks to a speed-up of Earth's rotation, the length of the astronomical day and the length of the clock day aren't quite matching up. Eventually, international timekeepers may need to subtract a second.

Category

🤖
Tech
Transcript
00:00The Earth's spin is speeding up.
00:03In 2020, the planet completed many of its revolutions around its axis milliseconds quicker than on average.
00:10That's a problem for Coordinated Universal Time,
00:14which uses ultra-accurate atomic clocks to meter out milliseconds, seconds, and minutes.
00:20The Earth's spin varies naturally due to the effects of the atmosphere, oceans, and core.
00:25But when atomic time and the length of the day determined by Earth's spin deviate by more than about 0.4 seconds,
00:34international timekeepers have to adjust the clocks.
00:38Until now, this has involved adding a leap second at the last minute of June or December,
00:43lengthening the day by the blink of an eye.
00:46That's because the overall trend in the Earth's rotation has been slowing.
00:51Until now.
00:52In 2020, Earth experienced its 28 fastest days since 1960.
00:59The quickest, July 19th, saw the planet spin around 1.4602 milliseconds faster than its average 86,400 seconds.
01:11If the trend continues, international timekeepers may eventually need a negative leap second,
01:18subtracting a second from the end of the day rather than adding one.
01:22The decision would be made by the International Earth Rotation and Reference Systems Service in Paris, France.

Recommended