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Thursday, 16 December, 1999, 21:35 GMT
Laser lights up London sky

The night sky The laser lights up the sky over London


A laser has been beamed into the sky over London to show the path of the Prime Meridian. The meridian marks the international timeline and will become a centre of celebrations in the UK on the night of 31 December.

The Millennia Vs green laser was turned on at the Royal Observatory Greenwich, which is sited in south east London. The path of the meridian runs in a circle through both poles and past the Millennium Dome, which has become a cultural icon for the year 2000.

Greenwich was voted as the location for the Prime Meridian of the world - zero longitude and the basis of the International Time Zone system - by the International Meridian Conference in 1884.


Greenwich laser The laser is illuminating the prime meridian
Diode lasers are used to produce the beam which will sweep out over the capital every evening.

The laser light is reflected off two mirrors and comes out of a hole in the old observatory building.

The light should be visible for more than 10 miles on a clear night, more on a cloudy night when the lights reflect off dust and cloud particles in the atmosphere.

The lasers, designed by US company Spectre Physics, are suspended in the roof of the building, seven metres above the precise location from where time was once measured.

Greenwich Mean Time (GMT) evolved as the world's official time reference and served the purpose until 1972. But the development of super-accurate atomic clocks saw the new Co-ordinated Universal Time (UTC) adopted internationally from 1972.

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