Today's Daily Photo is a screenshot taken from Google Earth - the desktop application that offers you "the world's geographical information at your fingertips".
As everyone knows, the Prime Meridian goes right through the Royal Observatory in Greenwich Park and some people actually pay £10 to go and stand by it. Next door to the Observatory, the Meridian is also marked by a line which goes through one of the tennis courts.
But Greenwich.co.uk reader Alwyne has spotted that the Prime Meridian as shown on Google Earth is some way out - over 100m, he reckons.
Alwyne is correct in his estimate - it's actually 102.5 metres east of Prime Meridian. The reason for this, apparently, is that that is where the World Geodetic System 1984 which is used by GPS satellites records the WGS84 meridian as being. For a better explanation than I could possibly muster of why this is, read on here.