Prime Meridian Day (1 November) celebrates the international conference in October 1884 that adopted the meridian through Greenwich, England as the foundation for global navigation -- zero degrees longitude. It is closely associated with Greenwich Mean Time, because mariners in the 1800s measured their longitude by calculating the difference between their local solar time and clocks calibrated for Greenwich time. The prime meridian is no longer defined by a physical line painted in the courtyard of the observatory at Greenwich but is "a statistical solution resulting from observations of all time-determination stations which the International Bureau of Weights and Measures (BIPM) takes into account when co-ordinating the world's time signals." My navigational tie features old-fashioned physical compasses.
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