Prepare for the ‘leap second’

IF life is often a matter of split seconds - the train door that closes in your face, the chance encounter with the love of your life - then the universe is about to bestow upon us a generous gift: the leap second.

On Saturday, at exactly midnight, one second will be added to our record of time: Co-ordinated Universal Time, kept by atomic clocks worldwide, certified by the International Bureau of Weights and Measures in Paris.

The reason for the extra second is simple: the Earth is slowing down. Since the days of Isaac Newton, scientists have understood the time it takes for the Earth to make a full rotation is getting longer. The gradual deceleration is caused by the gravitational pull of the moon. The same force that brings the tides is putting the brakes on the earth, albeit very slowly.

Because time is a function of planetary movement, our days are getting longer and, depending on how you look at it, time is slowing down. This discrepancy is something we have only become able to measure since 1958, with the advent of atomic clocks, which measure time using the resonant frequency of a caesium atom.

When a 24-hour day, as measured by the world’s atomic clocks, becomes more than 0.9 of a second shorter than a solar day, those in charge add the leap second.

Eventually the 24-hour day will become a few minutes longer, although it will take millions of years.

Most of us will not pause to notice the extra second. But computers, and mobile phones, and global positioning devices, will all rest for one second at the appointed time to calibrate coordinated universal time.

To witness the event, the process requires a stopwatch and a mobile phone with a time display.

At the precise moment the display reads 11.59 pm, start the stopwatch. When the display changes to 0.00am, stop the watch. It should read 61 seconds.

There. Your extra second will have been spent.