Our Spinning Planet Has Been Speeding Up

Does it seem as though the pace of life is increasing, that the world is going faster?

If it does, you're right, according to scientists.

Earth has been spinning faster in recent years. As a result, the world's timekeepers have decided - for the fifth successive year - not to insert an extra leap second at midnight this New Year's Eve.

Since 1972 the world's time scale, Co-ordinated Universal Time, or UTC, has been based on hundreds of highly accurate atomic clocks spread around the globe, including several in Sydney.

In the first 26 years of this system, 22 leap seconds had to be added to keep atomic time synchronised with time measured by the Earth's rotation, because of the globe's slightly irregular spin rate.

Peter Fisk of the CSIRO's National Measurement Laboratory, said that overall the Earth's rotation rate had been slowing over the past 100 years.

The use of leap seconds was necessary to make sure the time the sun rose was consistent from year to year. "Otherwise, in a few centuries, it would be rising later."

Dr Fisk said many factors could influence the rate of the globe's spin, including the movement of magma deep in the Earth and the melting of ice at the poles, leading to a sea level rise around the equator.
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"It's like a ballerina spinning on her toes who slows down when she extends her arms," he said.

Richard Brittain, secretary of the National Standards Commission's national time committee, said the moon's gravitational pull had a big effect, as did that of the planets as they moved close to and away from Earth on their orbits.

The reasons for the relative increase in Earth's spin speed during the past five years remain unclear.

The decision to add or subtract a leap second from co-ordinated universal time is made by the International Earth Rotation Service in Paris. It is carried out at midnight on either June 30 or December 31 - 10am on July 1 or 11am on January 1 on Australia's east coast.

Dr Brittain said that before the leap second was introduced, a "rubber second" was used to keep co-ordinated universal time in step with the Earth's rotation. The length of a rubber second was adjusted to ensure that the same number of seconds - 31,536,000 - made up one year.

"Altering the duration of a second was eventually felt to be both unscientific and far too complicated," he said.

Dr Fisk said the use of leap seconds had recently come under question by the time community.

The increasing number of electronic legal and financial transactions meant there was a risk of confusion if a deal was done during a leap second and a computer was not programmed properly to cope with the time change.

Without the accurate atomic time system, GPS navigation would be impossible and the position of heavenly bodies would not be known with enough accuracy for space probes to be launched and astronomical observations made.