Scientists to hold back time for one second on June 30Published On: Thu, Jun 28th, 2012 | Geology | By BioNews
The last minute of June 30, 2012 is destined to be 61 seconds long, as timekeepers will 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 stop 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.
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.
This will be the 25th intervention to add a “leap second” to UTC.
“Today, time is constructed, defined and measured with atomic clocks that are infinitely more stable than astronomical time. This allows us to ensure that everyone on Earth is on the exact same time,” the Telegraph quoted Noel Dimarcq, director of the SYRTE time-space reference system at the Paris Observatory as telling a foreign news agency.
TAI is kept by several hundred atomic clocks around the world, measuring fluctuations in the atom of the chemical element caesium that allows them to divide a single second into 10 billion smaller bits.
With such precision, “only one (atomic) second is lost every 300 million years,” said Dimarcq.
Every time the discrepancy between TAI and UT1 becomes too big, the International Earth Rotation and Reference Systems Service (IERS) jumps into action and announces a “leap second” – usually several months in advance.
The extra second is added to UTC, also known as Zulu time, only ever at midnight, either on a December 31 or a June 30.
Time-catching is as irregular as the Earth’ rotation itself. The last three adjustments were in 2008, 2005 and 1998.
The year 1972 saw two additions, followed the next seven years by a second every year.