While we all operate on the universal standard of 24 hours in a day, recent scientific observations suggest that some days are becoming infinitesimally shorter. Specifically, July 9 might go down in history as one of the briefest days ever recorded, with similar trends anticipated for future dates in July and August.
The familiar 24-hour duration of a day is fundamentally based on the time it takes for Earth to complete a single rotation on its axis, equating to roughly 86,400 seconds. However, experts from TimeAndDate have indicated that July 9 could be approximately 1.3 milliseconds shorter than average. The Tab, citing the International Earth Rotation and Reference Systems Service, even suggests this reduction could be as much as 1.6 milliseconds. This phenomenon of imperceptibly shorter days is also projected for July 22 and August 5.
What's Causing This Speed-Up?
The precise reasons behind Earth's accelerating rotation are still under investigation, but this trend has been consistently observed since 2020, with several days recording nearly a millisecond less than the norm. Notably, July 5, 2024, currently holds the official record for the shortest day, clocking in at 1.66 milliseconds less than the average.
Several theories attempt to explain this phenomenon. One hypothesis, as explored by Popular Mechanics, suggests that the Earth's varying distance from the moon could influence the planet's rotational speed. Conversely, research, including a study by NASA cited by USA Today, indicates that human activities are also impacting day length. Specifically, "dwindling ice and groundwater and rising seas" are thought to be contributing to days becoming incrementally longer by about 1.33 milliseconds. This suggests a complex interplay of natural and anthropogenic factors.
The Impact of Millisecond Shifts
For the vast majority of people, a change of 1.6 milliseconds is imperceptible; to put it in perspective, TimeAndDate notes that a human blink typically takes 100 milliseconds. So, the day will be shorter by dramatically less than the blink of an eye.
However, even these minute shifts in time can have significant implications for the advanced technology that underpins modern society. Dr. Michael Wouters, time and frequency lead at the National Measurement Institute in Australia, highlighted to The Guardian that critical systems like computers, GPS networks, and electricity grids can be thrown off by discrepancies as small as a billionth of a second. He specifically mentioned the vulnerability of banking systems, stating, "We’re transmitting data so quickly, and it all needs to be time tagged, so computers know what data goes where.”
If this trend of accelerating rotation continues, The Tab reports that a "leap second" might need to be introduced in 2029. This would involve recording a day as approximately one second longer to re-synchronize global timekeeping systems. A similar leap second was last added to atomic clocks in 2016, as noted in a report by the International Earth Rotation and Reference Systems Service.
It's also worth remembering that the length of an Earth day has historically fluctuated. During the age of dinosaurs, over 50 million years ago, a full rotation took only 23 hours. Projections suggest that in another two hundred million years, a day could extend to as long as 25 hours.
