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New Year's Eve extended by a second

Happy New Year

Irregularities in the way the Earth rotates means this year will be one second longer than last year. So, we'll have longer to enjoy New Year's Eve (Image: Reuters/David Gray)

Global timekeepers have decided to extend the last day of 2005 by one second, giving many people a little bit longer to enjoy New Year's Eve.

Time will stand still for a second at midnight, 31 December following a decision by the International Earth Rotation and Reference Systems Service to extend 2005 by a leap second.

The move is designed to bring the world's atomic clocks into sync with the Earth's rotation, says the head of time at Australia's National Measurement Institute Dr Bruce Warrington.

He says the extra second will be added at midnight Greenwich Mean Time, which for Australians means an extra second on the morning of 1 January 2006.

Atomic clocks use the vibration of caesium atoms as a pendulum and are accurate to a nanosecond or billionth of a second.

"They're more stable than the rotation rate of the Earth so if you count a day as the length of time it takes to spin once on its axis that varies more than atomic clocks do," Warrington says.

"So from time to time you have to add or in principle delete a second from time as it's told by clocks."

The system of leap seconds was first introduced in 1978 and this will be the first time a leap second has been added since 1998.

A shift in time

A number of factors can influence the rate at which the Earth turns, Warrington says.

These include tides, currents in the Earth's molten core, seasonal change or major tectonic movements like the Asian tsunami, which is estimated to have shortened the day by around two millionths of a second.

Warrington says while leap seconds used to be added every 18 months, it appears that the Earth's rotation has speeded up, enabling it to keep pace since 1998.

Who cares?

While some people may not be in a state to notice the extra second at midnight on New Year's Eve, others will watch the shift in time closely.

A change of just one second has implications for astronomers, technical observers, high-speed computing networks, security and time stamping of electronic transactions, Warrington says.

Officer in charge of CSIRO's Narrabri Observatory, Dr Bob Sault, says a one second jump is a big one in astronomical terms where time is kept in thousandths of a second.

"Our telescopes do point very accurately and so they need to know exactly where they're pointing in the sky," he says.

Warrington says global time authorities are discussing an alternative to leap seconds, which can be an administrative headache.

These could include letting the seconds accumulate and making bigger but less frequent changes, or more radically, changing the definition of a second.

Tags: astronomy-space, computers-and-technology