Greenwich Meridian Memorial

P Devine, on July 8, 2008, said:

Who has got the position wrong, Google or the town council? Zero Longitude according to Google is where the ground rises beyond the memorial.

jhr1uk, on July 9, 2008, said:

I think they could both claim to be correct – it depends which meridian you are using. The memorial appears to be on the thick ‘green line’ on the OS map. This covers both the Bradley (1750) and Airy (1851) alignment – the Airy being 19 feet east of the Bradley. I understand the line at the Greenwich Observatory is the Airy Meridian whilst OS use the Bradley. I’m not sure which of these the memorial is on.

Google Earth uses the WGS-84 (World Geodetic System 1984) meridian which puts zero longitude approx 102.5 metres to the east of the Airy meridian at Greenwich. WGS-84 is used by the American GPS system and is the default datum in most GPS units. Your satnav at Greenwich will show 00° 00' 00" Longitude to the East of the Greenwich line – corresponding with Google Earth and, it appears, a waste bin ! See:

http://www.nmm.ac.uk/server/show/conWebDoc.416 http://en.wikipedia.org/wiki/Prime_Meridian