Race against time: When a minute lasts 61 seconds

PARIS - Horologists around the world on Saturday will carry out one of the weirdest operations of their profession: they will hold back time.

The last minute of June 30, 2012 is destined to be 61 seconds long, for timekeepers are to add a "leap second" to compensate for the wibbly-wobbly movements of our world.

The ever-so-brief halting of the second hand will compensate for a creeping divergence from solar time, meaning the period required for Earth to complete a day.

The planet takes just over 86,400 seconds for a 360-degree revolution.

But it wobbles on its axis and is affected by the gravitational pull of the Sun and Moon and the ocean tides, all of which brake the rotation by a tiny sliver of a second.

As a result, Earth gets out of step with International Atomic Time (TAI), which uses the pulsation of atoms to measure time to an accuracy of several billionths of a second.

To avoid solar time and TAI moving too far apart, the widely used indicator of Coordinated Universal Time (UTC) is adjusted every so often to give us the odd 86,401-second day.

The adjustments began in 1972. Before then, time was measured exclusively by the position of the Sun or stars in relation to Earth, expressed in Greenwich Mean Time (GMT) or its successor UT1.

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