diamond geezer

 Friday, August 22, 2003

Famous places within 15 minutes walk of my house
Number 2 - the Greenwich meridian

zero degreesYes, that is exactly the same photograph of Abbey Mills that appeared here yesterday, snapped from atop the Northern Outfall Sewer. What you won't have spotted yesterday, however, was one of the most important lines in the world slicing the building in two. It's an imaginary line that heads north from here through Stratford bus station, Leyton, Chingford and Cleethorpes, and south through East India station, the Dome, a power station, Peacehaven, Burkina Faso and Ghana. It's the Greenwich meridian.

That imaginary line is a relatively modern invention. Nobody really cared about longitude until it became the key to successful ocean-going trade. Charles II established a royal observatory at Greenwich in 1675, hoping to boost Britain's chances on the high seas by plotting the positions of various heavenly bodies as accurately as possible. Key amongst the equipment here was the transit telescope, angled to move only up and down, and from 1750 it was this telescope that defined Britain's prime meridian. A new transit telescope was built at Greenwich in 1850 by the Astronomer Royal George Airy. It was positioned a short distance away from the original, and this resulted in the Greenwich Meridian being moved nineteen feet eastwards.

Nobody other than seafarers and astronomers would have realised that this line existed, neither did they need to know. Local noon was just whenever the sun was overhead, which was easy because people never travelled very far away from home in those days. Then came the railways, and suddenly it mattered that noon in London was five minutes later than noon in Norwich but nine minutes earlier than noon in Bristol. Railway time soon became Greenwich time, and clocks in towns and villages across Britain were quick to follow suit.

In 1884 the International Meridian Conference was convened in Washington DC. Representatives of 25 countries met to establish a single meridian so that time and dates could be standardised across the globe. Almost everybody supported Greenwich, except for the French who had established their own meridien through Paris. But it was Airy's meridian in Greenwich that was confirmed as the world's official line of zero longitude and the basis of the new International Time Zone system.

In the 21st century global navigation now relies on the satellite technology of GPS. Accurate measurements from space have led to another slight shift of the globe's most important line, and the GPS meridian now lies 102.48 metres east of the old Greenwich meridian. This page has a go at explaining exactly why this difference exists, but it's mighty complicated. (And ah, so that's why my own little GPS device has been giving me what looked like dodgy readings in the Greenwich area).

After dark a green laser beam shines out from the Greenwich observatory along the meridian. It marks a very special line, and yet a completely arbitrary one. This is the benchmark of both time and space, the line from which all days begin and the only line on earth on which local noon is still noon. In the eyes of the world, Greenwich means time.

<< click for Newer posts

click for Older Posts >>

click to return to the main page

...or read more in my monthly archives
Jan19  Feb19  Mar19  Apr19  May19  Jun19  Jul19  Aug19  Sep19  Oct19  Nov19  Dec19
Jan18  Feb18  Mar18  Apr18  May18  Jun18  Jul18  Aug18  Sep18  Oct18  Nov18  Dec18
Jan17  Feb17  Mar17  Apr17  May17  Jun17  Jul17  Aug17  Sep17  Oct17  Nov17  Dec17
Jan16  Feb16  Mar16  Apr16  May16  Jun16  Jul16  Aug16  Sep16  Oct16  Nov16  Dec16
Jan15  Feb15  Mar15  Apr15  May15  Jun15  Jul15  Aug15  Sep15  Oct15  Nov15  Dec15
Jan14  Feb14  Mar14  Apr14  May14  Jun14  Jul14  Aug14  Sep14  Oct14  Nov14  Dec14
Jan13  Feb13  Mar13  Apr13  May13  Jun13  Jul13  Aug13  Sep13  Oct13  Nov13  Dec13
Jan12  Feb12  Mar12  Apr12  May12  Jun12  Jul12  Aug12  Sep12  Oct12  Nov12  Dec12
Jan11  Feb11  Mar11  Apr11  May11  Jun11  Jul11  Aug11  Sep11  Oct11  Nov11  Dec11
Jan10  Feb10  Mar10  Apr10  May10  Jun10  Jul10  Aug10  Sep10  Oct10  Nov10  Dec10 
Jan09  Feb09  Mar09  Apr09  May09  Jun09  Jul09  Aug09  Sep09  Oct09  Nov09  Dec09
Jan08  Feb08  Mar08  Apr08  May08  Jun08  Jul08  Aug08  Sep08  Oct08  Nov08  Dec08
Jan07  Feb07  Mar07  Apr07  May07  Jun07  Jul07  Aug07  Sep07  Oct07  Nov07  Dec07
Jan06  Feb06  Mar06  Apr06  May06  Jun06  Jul06  Aug06  Sep06  Oct06  Nov06  Dec06
Jan05  Feb05  Mar05  Apr05  May05  Jun05  Jul05  Aug05  Sep05  Oct05  Nov05  Dec05
Jan04  Feb04  Mar04  Apr04  May04  Jun04  Jul04  Aug04  Sep04  Oct04  Nov04  Dec04
Jan03  Feb03  Mar03  Apr03  May03  Jun03  Jul03  Aug03  Sep03  Oct03  Nov03  Dec03
 Jan02  Feb02  Mar02  Apr02  May02  Jun02  Jul02 Aug02  Sep02  Oct02  Nov02  Dec02 

eXTReMe Tracker
jack of diamonds
Life viewed from London E3

» email me
» follow me on twitter
» follow the blog on Twitter
» follow the blog on RSS

my flickr photostream