Shortest measured day on Earth

The shortest day that has been measured since the invention of ultra-precise atomic clocks was 29 June 2022. According to the International Earth Rotation and Reference Systems Service, that day was 1.59 milliseconds shorter than the typical Earth day of 24 hours.

The length of Earth's days (the time taken to complete one full rotation) typically varies by about 3 milliseconds. Days are longer in the winter and shorter in the summer. This is due to a number of factors including the movements of the layers below the Earth's crust and the build-up of snow and ice around the poles.

For reasons no-one is entirely sure of, Earth's days have recently been growing incrementally shorter. The shortest day in 2019 was 0.95 milliseconds less than 25, but this shortfall increased to 1.47 and 1.46 milliseconds in 2020 and 2021, before dropping to 1.59 milliseconds less than usual in 2022. It has been speculated that this might be a consequence of shrinking glaciers and polar ice caps, which are relaxing the pressure on the Earth's crust near the poles. It may also be a result of the periodic oscillation of Earth's magnetic pole.