Greenwich Prime Meridian, England ? Just a second, 2009.

It’s going to take a little longer to say goodbye to a grim economic year, but all for good cause.

The custodians of time will ring in the New Year by tacking a “leap second” onto the clock today to account for the minute slowing of the Earth’s rotation. The leap second has been used sporadically at the Royal Observatory at Greenwich since 1972, an adjustment that has kept Greenwich Mean Time the internationally agreed time standard.

Some scientists now say GMT should be replaced by International Atomic Time, computed outside Paris, because new technologies have allowed atomic time to tick away with down-to-the-nanosecond accuracy.

But opponents say atomic time’s very precision poses a problem.

A strict measurement, they say, would change our very notion of time forever, as atomic clocks would one day outpace the familiar cycle of sunrise and sunset.

The time warp wouldn’t be noticeable for generations, but within a millennium, noon — the hour associated with the sun’s highest point in the sky — would occur around 1 p.m. In tens of thousands of years, the sun would be days behind the human calendar.

That bothers people like Steve Allen, an analyst at the University of California at Santa Cruz’s Lick Observatory.

“I think (our descendants) will curse us less if we choose to keep the clock reading near 12:00 when the sun is highest in the sky,” Allen said.

Atomic time advocates argue that leap seconds are onerous because they’re unpredictable.

Since the exact speed of the Earth’s rotation can’t be plotted out in advance, they’re added as needed. Sometimes, like this year, they’re added on Dec. 31, sometimes they’re inserted at the end of June 30.

Those fixes can trip up time-sensitive software. Critics say everything from satellite navigation to power transmission and cellular communication is vulnerable to problems stemming from programs ignoring the extra second or adding it at different times.