Tag archives: time

Walk the line: Airy meridian is marked as the “Prime Meridian of the World” (dotted line), and the modern reference meridian indicating zero longitude using GPS (solid line).
(Courtesy: 2014 Google Maps, Infoterra & Bluesky)

By Tushna Commissariat

A visit to the Royal Observatory in Greenwich is incomplete without walking along the Prime Meridian of the world – the line that literally divides the east from the west – and taking some silly photos across it. But you may be disappointed to know that the actual 0° longitudinal line is nearly 100 m away, towards the east, from the plotted meridian. Indeed, your GPS would readily show you that the line actually cuts through the large park ahead of the observatory. I, for one, am impressed that the original line is off by only 100 m, considering that it was plotted in 1884. A recently published paper in the Journal of Geodesy points out that with the extreme accuracy of modern technology like GPS, which has replaced the traditional telescopic observations used to measure the Earth’s rotation, we can measure this difference. You can read more about it in this article in the Independent.

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