No more leap seconds
There’s big news from the world’s official timekeepers! Starting May 20, 2027, the international time standard will no longer require leap seconds to keep it closely aligned with Earth’s rotation.
At the annual meeting of the General Conference on Weights and Measures on October 15, 2026, the group reported that it has adopted a resolution to effectively scrap the leap second and keep time running continuously.
It’s a small technical adjustment that addresses a surprisingly complicated problem. Earth doesn’t rotate at a perfectly steady rate, but our clocks need to keep time consistently. If you remember the hullabaloo surrounding Y2K, then you might have an idea why introducing an extra second now and then can wreak havoc on technology.
Currently, UTC (civil time, kept in Coordinated Universal Time) has to stay within one second of UT1 (solar time). But the new rule means they can get up to 1 hour apart until it would need adjusting again, which would likely take centuries. But no one knows just how long it would take, because Earth’s spin is fickle.
What is a leap second?
We measure time using extremely precise atomic clocks. But the time it takes Earth to rotate once isn’t perfectly constant. Earth’s rotation speeds up and slows down slightly. Why? Well, movements within our planet and the gravitational influence of the moon can all have a slight effect.
The world’s official time is Coordinated Universal Time (UTC). So, to keep it reasonably close to Earth’s rotation, timekeepers have occasionally added a leap second to clocks around the world. And recently they even discussed subtracting a leap second now and again.
These tiny adjustments help keep our clocks from drifting too far out of sync with the sun’s position in the sky.
Why is timekeeping changing?
The old system works, but it creates a problem for modern technology. Computers, satellite navigation, telecommunications networks and power grids rely on clocks that keep time smoothly and predictably.
Occasionally adding a leap second can cause software glitches. Removing a second, which could have become necessary, would be even more challenging. The resolution noted that there was a 30% chance a negative leap second would have to be implemented by 2035.
What will actually change?
The resolution says the difference between official time and time based on Earth’s rotation will be allowed to grow to as much as one hour. Only after that mark is breached would the official timekeepers look at fiddling with our clocks again.
But in practicality, none of us will notice a difference in our daily lives. Only over a very long period would we possibly notice the drift of time from the position of the sun. Of course, we already contend with changing seasons varying the time of sunrise and sunset and daylight saving time causing jumps, so these times are already not static in our experience.
Instead, the change should allow technology to continue flowing without glitches caused by leap seconds. And, as always, time marches on.
Bottom line: The world’s timekeepers announced on Thursday that leap seconds will no longer be added to clocks starting in May 2027. This change is designed to help our technology run smoothly.
Via Bureau International des Poids et Mesures
The post No more leap seconds! Timekeeping is officially changing first appeared on EarthSky.