UK Consults on Scrapping the Leap Second

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The UK government has started a consultation that could eventually see a gradual separation of solar time and the international coordinated timescale (UCT).

At the moment, occasional leap-seconds are added to the time zones around the world to account for the slight difference between the earth's irregular orbit and the mathematical purity of human built clocks.

However, because the periodic insertion of leap seconds can cause problems to systems such as computers and communications networks, there have been proposals to cease its use.

The UK's Science Minister David Willetts said: "My view is that without leap seconds we will eventually lose the link between time and people's everyday experience of day and night and this public dialogue will give everyone the opportunity to have their say on this important issue."

In 2015 the International Telcommunications Union (ITU) will take a decision about whether UTC should continue to be aligned with solar time or move to rely fully on atomic clocks.

Of course, it is more symbolic than practical link, as it would take millions of years before the clocks lost their real link with the planet's rotation. And human calendars have undergone far more radical changes in just the past thousand years.

Historically, time has been determined by the rotation of the earth and the location of the sun in the sky; in Greenwich Mean Time (GMT) noon is defined to be the mean time the sun reaches its highest point in the sky in Greenwich. However, the rotation of the earth is irregular and is also slowing-the length of the day is now (averaged out over several years) around 2.5 milliseconds longer than it was in 1820. This means that any time standard determined by accurate measuring devices like atomic clocks (such as UTC) slowly falls out of sync with solar time. In order to keep the two in sync leap seconds are added to (or, in principle, removed from) UTC to adjust for the irregularity in the earth's rotation. This ensures that UTC does not come apart from GMT by more than 0.9 seconds.

There have been 25 leap seconds since they were first introduced in 1972.

On the web: LeapSeconds

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