Delegates from 69 countries voted this week at the International Bureau of Weights and Measures to retire the leap second and adopt a leap hour from next year.
The backstory: Officials have added 27 leap seconds since 1972 to keep coordinated universal time in step with the rotation of the Earth, which the molten core, the oceans and global jet streams all nudge around.
Zoom in: The vote at Versailles lets universal time drift up to a full hour from astronomical time before a correction is needed, which on current estimates will take thousands of years.
Between the lines: The spin of the Earth has sped up over the past decade, creating a 30% probability this decade of a first negative leap second, where one minute would run 59 seconds. That risk pulled the vote forward.
- After the leap second applied in 2012, some operating systems failed to cope with a 61-second minute. Reddit and LinkedIn servers seized up and Qantas flights were delayed.
What they're saying: After 30 years of debate, the leap second is making way for the leap hour, said Setnam Shemar, principal scientist in time and frequency at the UK National Physical Laboratory, who sat on the committee that proposed the change.
- We already have daylight saving where we change by an hour and no one gets bothered about that, apart from losing sleep or getting an extra hour of sleep, Shemar said.
The other side: Britain long resisted dropping leap seconds because of the link with Greenwich mean time, and Russia opposed the move citing the impact on its Glonass satellite navigation system.
Why it matters: Telecoms, power grids, trading systems and satellites all run on high-accuracy time, and testing every connected system worldwide for an unprecedented negative leap second would have cost companies a fortune.
