Hang on a second – 2009′s arrival delayed
The arrival of the New Year will be a second later than expected thanks to a rare ‘leap second’ designed to make up for slowdowns in the Earth’s rotation. The pause has reawakened debates about whether we should switch to a more accurate way of keeping time.
The disparity is down to the way humans measure time. Originally it was simply a case of dividing the time it took for the Earth to rotate on its axis. As this was later found to be an inconsistent figure (once you start dealing with fractions of a second), the measure was later changed to be the relevant proportion of Earth’s annual revolution of the sun.
The problem is that this too is an inconsistent figure from year to year. As well as these annual variations, there’s an overall slowdown across the decades. To deal with these problems, scientists use two tactics.
Since 1967 the standard time measure has been calculated with atomic clocks, which use a fixed duration (taken from atomic vibrations) to measure a ‘second’ and thus take no notice of the Earth’s actual movements.
To take account of the overall slowdown, scientists keep track of the Earth and decide each year whether to add a leap second where clocks are effectively paused for a second to catch up with (or rather jump back to) the Earth’s movements. The system means there’s never more than one second’s disparity between the two measures.
This year will be only the second time in the past ten years when there has been such a leap second. It will take place at one second to midnight Greenwich Mean Time (one second before 7pm Eastern Standard Time).
Time experts are divided on whether we should keep the leap second system. Critics say it causes problems with electronic devices: some are linked to atomic clocks while others are not, which can confuse some devices that find themselves a second out of synch. A US Naval Observatory spokesman says, “Leap seconds turn out to be more of a pain in the neck than Y2K ever was.”
However, defenders of the leap second say abandoning it would mean losing the link between our concept of time and the actual movements of the Earth. In the short term it would make no practical difference, but within a thousand years there’d be a one-hour gap between ‘noon’ and the sun reaching its highest point of the day.
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