'Leap second' to keep kiwi clocks in step with slowing globe

'Leap second' to keep kiwi clocks in step with slowing globe

New Zealand’s Measurement Standards Laboratory (MSL) is coordinating the insertion of a ‘leap second’ into the atomic time scale at noon July 1, New Zealand Standard Time, to ensure the smooth running of industrial and scientific applications around the country, says MSL Director Dr Tim Armstrong.

When the leap second is added, the atomic clocks at MSL – part of Industrial Research Ltd - will, unusually, display ‘11.59.59’, ‘11.59.60’ and ‘12.00.00’, while listeners to Radio New Zealand National will experience it as an extra time ‘pip’ before the midday news bulletin.

The decision to add a leap second is made on an irregular basis by the International Earth Rotation Service located at the Paris Observatory, which collects data from observatories around the world to precisely determine the length of the day, says Dr Armstrong.

“Without leap seconds, eventually our clock time would get out of step with the time of day we expect from the location of the sun in the sky,” he says. “If they were not introduced then eventually the solar midday would occur at midnight.”

This year is the 40th anniversary of the creation of leap seconds in 1972 as part of the shift of the international time scale to atomic time (known as UTC, or coordinated universal time), which removed the direct link between clock time and the rotation of the earth. They were created to ensure the atomic time scale never differed from the rotation of the earth by more than 1 second.

“At the introduction of leap seconds, the atomic time scale was set to the length of one day,” says Dr Armstrong. “However the rotation of the earth is gradually slowing down (due to the drag of tides and other effects) and the duration of a day is getting longer.”

Customers reliant on the correct provision by MSL of atomic time range from internet service providers to broadcasters such as Radio New Zealand (whose Time ‘Pips’, broadcast every hour, are based MSL’s caesium atomic clocks).

“Since 2000, there has been much discussion about abandoning leap seconds, which are considered a nuisance for people wanting to maintain continuous time scales,” says Dr Armstrong. “Leap seconds cannot be calculated because they are added at irregular intervals and because knowledge of the exact time of each leap second is required, determining time differences with 1 second resolution difficult to calculate. A similar problem occurs with leap years but because they are regular, it is possible to calculate when they occur.”

A meeting was held in January of this year to decide the fate of leap seconds but was unable to reach agreement. A further meeting in 2015 will reconsider the matter.

About MSL (msl.irl.cri.nz)

MSL is New Zealand's national metrology institute and part of Industrial Research Ltd (IRL), a government owned research institute working to support industry through the application of science and engineering excellent. MSL’s world-class services include a wide variety of calibration, specialist measurement and expert consultancy services and measurement R&D.

The caesium clocks at MSL maintain New Zealand’s standard time to nanosecond (billionths of a second) accuracy (the international standard ‘second’ was defined in 1968 on the unchanging vibration of caesium atoms).

MSL computers linked to the caesium clocks service over three million time requests from New Zealand computers every day.

ENDS

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