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The Time Has Come To Kill The Leap Second, Timekeepers Decide

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Ben Taub

Freelance Writer

clockNov 22 2022, 14:17 UTC
Leap second
It's not yet clear how atomic and astronomical time will be kept in sync without the leap second. Image credit: kitti Suwanekkasit/

The world’s time lords – otherwise known as the International Bureau of Weights and Measures (BIPM) – have voted to scrap the leap second by 2035. By allowing time to simply run its course without intermittently meddling, the organization hopes to bring an end to decades of niggling disruptions to the world’s technological systems.

The leap second was first introduced in 1972 as a means of counteracting the discrepancy between astronomical and atomic timekeeping scales. While both systems agree that a 24-hour day contains exactly 86,400 seconds, the differing means by which they define the length of a second results in an infinitesimally small, yet hugely significant, glitch in time.


More precisely, the astronomical second is determined by dividing the length of time it takes the Earth to complete one rotation by 86,400, while the atomic second lasts for exactly 9,192,631,770 vibrations of a cesium 133 atom. And while these two units are almost identical, the gradual slowing of the Earth’s rotation means that the length of the astronomical second increases ever so slightly over time.

Atomic clocks therefore end up marginally ahead of astronomical time, and the leap second was devised as a means of realigning the two systems. Essentially, whenever atomic time gets one second ahead, it stops for a second so that the rotation of the Earth can catch up.

Occurring once every few years, these tiny adjustments are imperceptible to the average biological Earthling, yet cause major headaches for our technological neighbors. For instance, computer systems that rely on exact timekeeping occasionally crash when the leap second messes with their calculations.

Telecommunications infrastructure, satellite navigation and all manner of software struggle to deal with the interruptions to the flow of time, while the fact that leap seconds are not periodical exacerbates the situation by making it difficult to predict when they will occur. The first ten leap seconds were introduced when the workaround was first conceived half a century ago, and 27 more ticks and tocks have been inserted into the atomic time scale in the years since.


By keeping the two timelines in sync, leap seconds enable the BIPM to maintain Coordinated Universal Time (UTC), the official timekeeping system by which all clocks are set. However, because of the problems caused by leap seconds, some technological programs have abandoned UTC and utilize their own measurements instead. Perhaps the most notable example is GPS, which keeps time according to a different method that does not include episodic adjustments.

The BIPM’s decision to abandon the leap second was taken in part to encourage greater adherence to UTC by making it a more seamless timescale. Patrizia Tavella, who leads the BIPM's time department, told AFP that the change would result in "a continuous flow of seconds without the discontinuities currently caused by irregular leap seconds".

Of course, this means that the difference between atomic and astronomical time will be allowed to grow to more than a second, and some sort of realignment will therefore be required at a later date. The degree to which the two timelines will be permitted to diverge, and the method by which they will be brought back into sync once leap seconds are a thing of the past, have yet to be decided. 

Negotiations to find a solution are expected to take place between now and 2035, when the new time regime comes into effect.

spaceSpace and Physicsspacephysics
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