The Prime Meridian

This rather unprepossessing strip of metal is set into the pavement of Eastgate in Louth, Lincolnshire and marks the line of what is now generally referred to as the Greenwich Meridian.
So here I stood this morning in the Western hemisphere gazing into the Eastern half of the world, before stepping across into it!
The prime meridian, based at the Royal Observatory, Greenwich, was established by Sir George Airy in 1851. By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their maps. In October of that year the International Meridian Conference selected the meridian passing through Greenwich as the official prime meridian due to its popularity. Typically, the French abstained from the vote and their maps continued to use the Paris meridian for several decades.

The Prime Meridian passes through the Greenwich observatory in London. It was long marked by a brass strip in the courtyard, now upgraded to stainless steel (similar to this one in Louth) and, since 16 December 1999, has also been marked by a powerful green laser shining north across the London night sky. Have you seen it?