Prime Meridian Laser
November 09, 2016
Photographer: Miguel Claro
Summary Author: Miguel Claro
The Greenwich Meridian separates east from west as the Equator separates north from south. It's the basis for our system of time zones and Greenwich Mean Time (GMT). Established by Sir George Airy in 1851, its path is determined by the location of a historic telescope (the Airy Transit Circle), part of the Royal Observatory of Greenwich in London, England.
The Prime Meridian in Greenwich Observatory was long marked by a brass strip in the Observatory courtyard, but it's now been replaced by stainless steel and, since December 16, 1999, has been marked by an eye-catching green laser shining north across the London night sky. On the photo above, west is to the left. In good seeing conditions this powerful laser can be detected from about 36 mi (58 km) away.