It might feel like there is never enough time, but Earth has gained 27 seconds since the 1970s – an astronomical quirk which is causing a headache for timekeepers.

On New Year’s Eve, experts at the National Physical Laboratory (NPL) in Teddington, London, will add a leap second to UK time to account for the fact that the Earth is now spinning more slowly.

Immediately before midnight, dials will read 11:59:60 as clocks around the world pause for a second to allow the Earth’s rotation to catch up with atomic time.

“Inserting a leap second is necessary because the Earth is wobbling and slowing down” Dr Leon Lobo

The first leap second was added in 1972, so it will be the 27th time it has been added to clocks in history, meaning that everyone has gained 27 seconds over the past 44 years.

Dr Leon Lobo, of NPL’s time and frequency group, said: “Most people won’t even notice, although everyone will probably be celebrating New Year a second too early this year.

“People might also notice problems with mobile phone networks as they work on atomic time and, with the increased traffic on New Year’s Eve, there could be potential issues.

“Inserting a leap second is necessary because the Earth is wobbling and slowing down and over time that divergence could cause problems.”

Atomic clocks, on which the modern world now runs, keep time by measuring the movements of electrons in cesium atoms.

Consequently, atomic time is constant, but the Earth’s rotation slows by about two thousandths of a second per day. At the time of the dinosaurs, Earth completed one rotation in about 23 hours.

So leap seconds are, therefore, essential to ensuring atomic time does not move away from time based on the Earth’s spin. If it isn’t corrected, such a drift would eventually result in clocks showing the middle of the day occurring at night.

Although the drift is small, if not corrected it would eventually result in clocks showing midday before sunrise” Peter Whibberley

While it would take hundreds of years for the difference to become obvious to most people, modern satellite communication and navigation systems rely on time being consistent with the conventional positions of the sun, moon and stars to within a fraction of a second.

If the two standards were allowed to further out of synch, they would differ by about 25 minutes in just 500 years.

Peter Whibberley, senior research scientist with NPL’s time and frequency group, who is known as ‘the time lord’, said: “Atomic clocks are more than a million times better at keeping time than the rotation of the Earth, which fluctuates unpredictably.

“Leap seconds are needed to prevent civil time drifting away from Earth time. Although the drift is small – taking around 1,000 years to accumulate a one-hour difference – if not corrected it would eventually result in clocks showing midday before sunrise.”

It is the task of scientists and officials at the International Earth Rotation Service, based in Paris, to monitor the planet’s rotation and inform countries when leap seconds must be added six months in advance.

 

Typically, leap seconds are added every two or three years, although the last one was inserted just 18 months ago in June 2015.  Some years, the Earth runs bang on time and no adjustment is needed. It is also possible for a second to be removed from the UTC (Universal Co-ordinated Time) timescale, although this has never happened.

BT’s speaking clock will add a second’s pause before its third pip and Radio 4 will also add an extra pip to its 1am bulletin.

But there can be consequences of tinkering with time. When a leap second was added in 2012, Mozilla, Reddit, Foursquare, Yelp, LinkedIn and StumbleUpon all reported crashes and there were problems with the Linux operating system and programmes written in Java.

Because leap seconds are only introduced sporadically, it is difficult to implement them in computers and mistakes can cause systems to fail temporarily.

Many computing systems use the Network Time Protocol, or NTP, to keep themselves in sync with the world’s atomic clocks. But most are not programmed to deal with an unexpected extra second.

Google has even developed a special technique to deal with what it refers to as a “leap smear” and has been gradually adding milliseconds to its system clocks prior to the official arrival of the leap second.

The US wants to get rid of leap seconds, claiming they are too disruptive to precision systems used for navigation and communication. But Britain opposes the change, saying that it would forever break the link between our concept of time and the rising and setting of the sun.

Experts fear that, once this link is broken, it could never be restored because, although the Earth’s timekeeping systems are built to accommodate the occasional leap second, adding a leap minute or hour to global time would be virtually impossible.

The World Radiocommunication Conference was due to decide on the fate of the leap second at last year’s meeting, but has deferred the decision until 2023.