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So what will you do with your extra second tomorrow night?

Rare leap second to be added to atomic clocks on Saturday night

It oftens feels like there are not enough hours in the day. But are there enough seconds?

The answer is no - according to the impressively named Earth Rotation and Reference Systems Service (IERS).

The IERS, which is responsible for keeping track of the gap between atomic seconds and planetary time will be adding an extra so-called 'leap second' to their atomic clocks this weekend.

On Saturday night, therefore, atomic clocks will read 23 hours, 59 minutes and 60 seconds, before moving onto Greenwich Mean Time at midnight.

The main reference point for how we set out watches are super-accurate atomic clocks. However, the precision of such clocks - which are much more constant than the shifting movement of the earth - can lead to discrepancies.

Uncorrected the leap second would continue to move further ahead leading to, in many years, the sun setting at midday. A leap second performs a similiar function to an extra day in a leap year, which keeps the calendar in time with the seasons.

In recent years a leap second has been added to the atomic clocks every few years, at a slightly more infrequent rate than in the 1970s.

This is despite the long-term slowing of the rotation of the earth caused by earthquakes, tides and other natural phenomena.

"We want to have both times close together and it's not possible to adjust the earth's rotation," Daniel Gambis, head of the Earth Orientation Centre of the IERS said.

Atomic clocks are used to set Coordinated Universal Time, making the adjustments to them more than just a technical oddity.

Time standards on the internet, satellite navigation systems, air traffic control sytems and banking computers are set using the Coordinated Universal Time system.

But the leap seconds are not uncontroversial, and there have been calls for them to be abandoned.

A meeting of the International Telecommunications Union (ITU), the UN agency responsible, failed to reach a decision in January.

People who oppose the leap second want a simpler system, that avoids - they say - some of the costs and margins for error in making the thousands of corrections.

Britain's Royal Astronomical Society says the leap second should be retained until there is a much broader debate on the change.

"This is something that affects not just the telecom industry," said RAS spokesman Robert Massey. "It would decouple time-keeping from the position of the sun in the sky and so a broad debate is needed."

Time standards are important in professional astronomy for pointing telescopes in the right direction but critical systems in other areas, not least defence, would also be affected by the change.

"To argue that it would be pain free is not quite true," Massey said.

Meanwhile people across the UK are unlikely to notice the occurrence of the shortest  long weekend this year.