sexta-feira, 29 de junho de 2012

Race against time: When a minute lasts 61 seconds

Horologists around the world are about to carry out one of the weirdest operations of their profession: they will hold back time. The last minute of 30 June 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.

Planetary wobble 'brakes' rotation
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. Read more.

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