Global atomic time changes are coming as leap seconds are scheduled to vanish under a decision finalized on October 15, 2026, by the 28th General Conference on Weights and Measures (CGPM), sol.de reported.
The coordinated universal time relies on atomic clocks, while astronomical time is determined by the rotation of the Earth.
Because atomic clocks measure constantly while the Earth’s rotation speed can fluctuate, the two time scales deviate slightly. To realign them, the procedure of leap seconds was introduced in 1972 so that the scales would not deviate by more than 0.9 seconds. This has been done 27 times, most recently in 2016.
While leap seconds generally have no direct effect on humans, they can cause disruptions in computer systems. Critical infrastructures such as power supply, telecommunications, traffic, and other digital systems depend on constant and globally uniform time synchronization.
Because the Earth’s rotation has accelerated at times in recent years, there was a possibility that a second might have to be subtracted instead of added. Such a negative leap second has never happened before, and it remains unclear whether it could be implemented smoothly in all technical systems.
To avoid technical risks, it was decided that the coordinated universal time will be allowed to deviate more strongly from astronomical time starting May 20, 2027. Instead of 0.9 seconds, the deviation may total up to 3,600 seconds, which equals an hour.
For consumers, nothing will change in everyday life, as no clocks will need to be adjusted and there are no changes to summer or winter time. Practical effects will mainly impact people working with astronomical time, as it can deviate significantly from world time. This affects employees in astronomy, astrophysics, meteorology, observatories, earth surveying, space travel, and satellite technology.
