Timekeepers around the world are abolishing the leap second, the extra second occasionally added to clocks to keep them in step with Earth’s rotation.
The change is an attempt to avoid problems in satellite systems and other critical technology caused by the extra seconds.
The metrologists will meet in Paris in October to officialise the decision, and New Zealand has a seat at the voting table.
The SMC asked experts to comment.
Dr Adam Dunford, Senior Research Scientist, Measurement Standards Laboratory & NZ’s Time Lord*, comments:
“Leap seconds have been added since 1972 to keep solar and atomic time aligned. Unfortunately, most software assumes minutes have 60 seconds, so irregularly inserted extra seconds cause major headaches where computer synchronisation is concerned.
“Equally unfortunately, there is no universally adopted way for ‘inserting’ a second, especially in software which only allows 60 per minute. MSL’s atomic clocks just add one more second and display 23:59:60.”Added days in leap years, by contrast, follow a predictable rule, which software can accommodate. Leap seconds occur irregularly and are announced only six months in advance, based on measurements of Earth’s rotation. Computer systems have to maintain lookup tables of when each one happened. It’s a book-keeping burden.
“It’s caused real problems before – outages in airline booking systems and other major online services have been traced to leap second transitions.
“Although Earth’s rotation has been slowing for millennia, largely due to tidal friction, this slowdown has recently slowed for a range of complex reasons including shifts in groundwater and ice-mass distribution. That’s opened up a real, if modest, chance we will need to remove a second. No computer system has ever had to handle this, and there is little confidence it will go smoothly.
“Increasing the allowed difference between atomic time and Earth’s rotation to 3600 seconds (1 hour) makes the mismatch something we can safely ignore for a very long time, giving industries relying on precise timing room to plan rather than react. In essence, we are choosing the more stable, predictable ‘ruler’ – atomic time – much as earlier generations chose railway time over local solar time.”
*Note: Dr Dunford is keeper of the atomic clocks behind NZ Standard Time, and known informally as the country’s “Time Lord”.
Conflict of interest statement: “I have no conflict of interest. I want NZ to have the best Time possible and for it to be freely, and widely, available.”
Dr Peter McDowall, Director and Chief Metrologist of the Measurement Standards Laboratory, comments:
One resolution is to abolish the implementation of leap seconds. Since 1972, leap seconds have been used to keep Earths official time, Universal Coordinated Time (UTC, measured by atomic clocks), in sync with Earth’s natural rotation to within 1 second. If adopted by majority vote at the CGPM, the leap second will be replaced by a leap hour.”This isn’t a fix so much as a very long postponement, a leap hour will only need to be introduced whenever Earth’s rotation drifts up to an hour out of step with atomic time. In contrast to the 27 leap seconds that have been implemented since they were first introduced, a leap hour may be required once every few hundred, if not a thousand, years.
“It also heads off a more immediate concern: current predictions give roughly a 30% chance we’ll need to subtract a leap second within the next five years. This is not something we’ve ever had to do before and are quite frankly unprepared for.
“An hour was chosen partly because many countries already shift their clocks by an hour for daylight saving, so the social licence already exists.
“As NZ’s Chief Metrologist, I’ll be casting our vote; not on behalf of MSL, but as instructed by the New Zealand Government, informed by New Zealand’s time keeping experts.
“To be clear about what isn’t changing: this vote doesn’t touch the definition of the second itself. That’s a separate, ongoing discussion which will be addressed at a future CGPM.”
Conflict of interest statement: Dr Peter McDowall is the Chief Metrologist at Measurement Standards Laboratory and will be taking part on the vote, representing NZ.
Professor Sergei Gulyaev, Radio Astronomy Modelling and Statistics, Auckland University of Technology, comments:
“I think adopting a leap hour instead of leap seconds is a reasonable option. Astronomers and astronomy students would still learn about the irregularity of Earth’s rotation and the difference between astronomical and civil time, while the general public would not need to deal with occasional time adjustments.
“Over the past 50 years, a total of 17 leap seconds have been added to compensate for the gradual slowing of Earth’s rotation, corresponding to roughly one second every 2–3 years. If this trend were to continue at a similar rate, it would take on the order of 7,000 years for the accumulated difference to reach one hour.
“From this perspective, a leap hour appears to be a practical long-term solution. It would require astronomers and some technical users to account for the growing offset between civil time and Earth’s rotation, but this is a relatively small community compared with the population affected by civil timekeeping.”
Conflict of interest statement: “No conflict to declare.”
Dr. Emily O’Hara, School of Art & Design, Auckland University of Technology, comments:
“Since 1972 humans have added leap seconds in a bid to maintain consistency between Earths rotational speed and atomic clocks, the technological advancement that positions how we understand clock time. We invented an extraordinarily precise instrument for measuring time and are now confronted by the fact that the Earth does not behave like a clock. UTC is an enormous international infrastructure for agreeing what time it is, with scientists’ world-over working together to maintain its precision. The leap second exposes the negotiation normally hidden inside that apparently objective fact.
“The impacts of the leap second are widely known in terms of impact on the systems that keep the world turning, its addition causes outages across major platforms and operating systems. With these impacts well established, the technological rationale for changing the system is substantial. Instead, I consider the leap second to be a conceptual crack through which we can see that clock time is constructed, planetary time is unruly, and our attempts at perfect synchronisation are futile.
“We have two extraordinarily different ways of knowing time, one produced through atomic regularity and the other through observing a moving planetary body. We live with an embodied understanding of both temporal expressions; we hear church bells ring, clocks tick, accept calendar invitations, we see the stars move, the sun shift across the sky, the moon come and go and seasons that change.
“For fifty years, we’ve been making tiny adjustments to keep these ways of knowing time closer together. Now we are considering allowing them to separate. No matter the outcome at CGPM, the leap second, or leap hour that it may become, acts as a tiny reminder that keeping time is something that happens between us, and a large array of celestial bodies outside of our control.”
Conflict of interest statement: I have no conflict of interest, receive no research funding from any associated areas.