Leap second to remain for another three years

The ITU Radiocommunication Assembly has decided to hang on to the leap second for three more years, keeping the world’s atomic clocks in synch with the Earth’s rotation.

The reason the leap second is needed is that the rotation of the Earth is – very gradually – slowing. Without the occasional addition of a leap second to the year, ‘clock time’ would eventually lose its relationship with the cycle of day and night.

The leap second was first introduced in 1972, and is managed by the International Bureau of Weights and Measures (BIPM).

Measurements from timing centres around the world are used to determine Coordinated Universal Time (UTC), which is adjusted to within 0.9 seconds of Earth rotation time, as determined by the International Earth reference and Rotation Service (IERS).

However, some countries, in particular the US, had wanted to eliminate leap seconds because of the difficulties they create for computer communications.

And the reason the decision’s been deferred is to allow time to consider all the technical options and implications, says the ITU.

“The suppression of the leap second would make continuous time scale available for all the modern electronic navigation and computerized systems to operate with and eliminate the need for specialized ad hoc time systems,” the committee reports.

“This, however, may have social and legal consequences when the accumulated difference between UT1 – Earth rotation time – would reach a perceivable level (two to three minutes in 2100 and about 30 minutes in 2700).”

The committee will debate the issue again at its next meeting in 2015 – a little later than would have been the case if the decision had gone the other way, as a new leap second’s due to be added this June.