Planet Earth is spinning a little faster today — resulting in one of the shortest days of the year. But the change will be so minuscule you won’t even notice. We’re talking even less time than the blink of an eye.
In fact, several milliseconds will be shaved off the 24 hours it takes for Earth to complete a full rotation on July 9, July 22 and Aug. 5 due to changes in the speed of the Earth’s rotation.
Why is Earth’s rotation speed changing?
Planet Earth is our timekeeper, but it’s not perfect.
It takes our planet 24 hours — one day — to complete one full rotation on its axis, which breaks down to 86,400 seconds. But Earth’s rotation could change by a millisecond (.001 seconds) or two every day.
The orbit of the moon can have an effect on how fast the Earth spins around. “Our planet spins quicker when the moon’s position is far to the north or south of Earth’s equator,” according to TimeandDate.com.
“Earthquakes, volcanoes, tidal forces, subterranean geology, and many other mechanisms can cause the planet’s rotation to slow down or speed up, and those micro-adjustments can trend over time,” Popular Mechanics reported.
The 8.9 magnitude earthquake that struck Japan in 2011 accelerated Earth’s rotation, shortening the length of the standard 24-hour day by 1.8 microseconds (0.0018 milliseconds).
These tiny day-to-day fluctuations in the Earth’s spin speed began to be measured in the 1950s with atomic clocks. Any number above or below the standard 86,400 seconds is called the length of day (LOD).
The shortest day recorded was on July 5, 2024, when Earth completed its full rotation 1.66 milliseconds faster than the standard 86,400 seconds.
When will this happen?
There are a total of three days this summer — July 9, July 22 and Aug. 5 — when the moon will be around its furthest distance from Earth’s equator, resulting in a minuscule increase in the Earth’s spin speed. According to Space.com, here are the lengths of those days:
July 9: Day shortened by 1.23 milliseconds
July 22: Day shortened by 1.36 milliseconds
Aug. 5: Day is shortened by 1.25 milliseconds
Wait — isn’t there another day that’s considered the shortest of the year?
What feels like the shortest day of the year in the Northern Hemisphere is known as the winter solstice, when Earth is tilted away from the sun at its maximum. This results in the fewest amount of daylight hours all year and occurs in mid-December.
Will Earth always have 24 hours in a day?
There weren’t always 24 hours in a day. Researchers believe that in the Jurassic Period, it took Earth just 23 hours to make a complete rotation around its axis. Scientists have found that the length of a day on Earth is increasing each century by about 1.7 milliseconds. Over time, that adds up. Experts think that 200 million years from now, there will be 25 hours in a full day.
