Extra second of time on Sunday

People are being given an extra second of time this Sunday as scientists insert a leap second into the atomic time scale.

At noon on Sunday New Zealand time, corresponding to midnight on June 30 in UTC (Coordinated Universal Time) scientists will hold back time for a second in order to ensure the smooth running of industrial and scientific applications around the country.

MSL director Dr Tim Armstrong says when the leap second is added, the atomic clocks at MSL will unusually, display ‘11.59.59’, ‘11.59.60’ and ‘12.00.00’, while listeners to Radio New Zealand listeners will experience an extra time ‘pip’ before the midday news bulletin.

He says 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.

“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.

“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 one second.

“At the introduction of leap seconds, the atomic time scale was set to the length of one day.

“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 are 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.

“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.”

Tim says 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 parties involved were unable to reach an agreement.

A further meeting will be held in 2015 to reconsider the matter.