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East meets West at the Prime Meridian Line

Updated: Jan 29, 2018

Written by Lakshini Mendis |


Stand astride the historic Prime Meridian Line at the Royal Observatory in Greenwich, England... it's where east meets west at longitude 0°.

Image by originalpickaxe [CC BY 3.0], via Wikimedia Commons


The Greenwich Royal Observatory museum is a must-see for anyone interested in astronomy or horology. It offers a fascinating glimpse into time and space, with displays of astronomical and navigational tools. Named after the first Royal Astronomer, John Flamsteed, the Flamsteed House (another Wren masterpiece), which is the historic home of Royal Astronomers, now offers an ode to astronomers past, including Caroline Herschel. Pleasures of Astronomy, a board game devised by Margaret Bryan (a keen advocate of girls’ education), during the early 19th Century, is also on display.

Of course the Greenwich Royal Observatory’s main draw is the historic Prime Meridian Line.


The Greek geographer, Ptolemy, was the first person to consistently use the idea of longitudes and a meridian. The meridian is a north-south line that is selected as the zero-reference line for astronomical observations. You can build an accurate map of the sky by comparing thousands of observations acquired from the same meridian.


Since the Greenwich Royal observatory had been churning the best available navigational data, at the time, for hundreds of years, the Greenwich Royal Observatory meridian in London was frequently used as the universal reference point, between 1765 and 1811.

It was finally voted as the Prime Meridian of the World, in Washington, in 1884. At that time, the Greenwich Royal Observatory meridian was defined by the cross-hairs of the eyepiece of the large 'Transit Circle' telescope in the Observatory, which was built by Sir George Biddell Airy, the 7th Astronomer Royal, in 1850.


Once defined as the Prime Meridian of the World, it also served as the reference line for universal time, hence the term, Greenwich Mean Time. By then, there an increasing need worldwide for an international time standard because of the expansion of the railway and communication networks. Before then, most towns had kept their own local time, with no national or international conventions on how time should be measured, the length of an hour, or when the day would begin and end.


Given that the Earth’s crust is moving, the exact position of the Prime Meridian also continues to shift very slightly. So, although the historic prime meridian line continues to attract hundreds of tourists found around the world each year, the International Reference Meridian, which is actually used now to set time and the GPS coordinates in your SatNav, is actually located 102.5 m east of it, apparently “cutting unceremoniously through a footpath, not far from a rubbish bin.”


Explore more (and book your tickets) here.

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