On June 29, 2022, the Earth completed its shortest rotation ever recorded. Usually, the Earth rotates on its axis in a little under 24 hours. That’s what makes what’s called sidereal days. Solar days, on the other hand, mark how long it takes the Earth to spin on its axis so the Sun appears in the same place in the sky. On average, sidereal days are about 4 minutes shorter than solar days.
But, last month, Earth saw its shortest solar day. The Earth completed its rotation 1.59 milliseconds under 24 hours, according to TimeAndDate.com. This set a record for the shortest day since we started using atomic clocks in the 1960s. Scientists can’t really figure out the reason for the speed-up in June, but there are some theories. As reported by Interesting Engineering, some scientists think the melting ice caps contribute to less weight on the poles, which equals a faster spin. Others speculate that the Earth’s molten core is moving. A faster spin could also be influenced by seismic activity. Or there’s something called the “Chandler wobble,” which refers to a deviation in the Earth’s rotation on its axis. According to Dr. Leonid Zoltov of the Sternberg Astronomical Institute, Earth’s Chandler wobble disappeared between 2017 and 2020.
So, there are a few theories as to why this is happening, but no real answer. Also, it’s important to note the Earth’s rotation speed has fluctuated through the centuries. It generally speeds up and slows down a few times by a fraction of a millisecond from day to day. While June 29 was the shortest day on record so far, Earth almost beat itself out again on July 26 with a day that lasted 1.50 milliseconds under 24 hours.
Earth is Spinning Faster This Year, Could We Be Forced to Introduce a Negative Leap Second?
There’s one notable problem with the Earth spinning faster. We tell time by the steady beat of atomic clocks pairing up with solar time based on the movement of the Sun. This is called civil time. But, if the days are shorter, we may be forced to introduce negative leap seconds in order to keep civil time.
When days are noticeably longer–when the Earth’s rotation shows–we use leap seconds to keep civil time. The last time we needed a leap second was on December 31, 2016. The last minute of 2016 lasted 61 seconds because the Earth’s rotation had slowed. Now, if it spins much faster, we may need to add a negative leap second. This means we skip a second instead of adding one. This could potentially cause some problems with IT systems and computer hardware.
According to TimeAndDate, Dr. Zoltov doesn’t think we’ll have to resort to the negative leap second because we’re already at the minimum length of day. “I think there’s a 70 percent chance we’re at the minimum,” he told the outlet, “and we won’t need a negative leap second.”