Prime Meridian Laser in Greenwich


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The Greenwich Meridian separates east from west in the same way that the Equator separates north from south. Inextricably linked with Greenwich Mean Time, it also sits at the centre of our system of time zones. Its path is determined by the location of an historic telescope, the Airy Transit Circle (51°28′40.1″N 0°0′5.3″W), which is housed at the Royal Observatory of Greenwich, in London. The Prime Meridian was established by Sir George Airy in 1851.

A prime meridian is a meridian (a line of longitude) in a geographical coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its antimeridian (the 180th meridian in a 360°-system) form a great circle. This great circle divides the sphere, e.g., the Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian, then they can be called Eastern Hemisphere and Western Hemisphere.

PT: O meridiano de Greenwich separa “Este” de “Oeste” da mesma forma que o Equador separa o Norte do Sul. Intimamente ligado com Greenwich Mean Time, também está no centro do nosso sistema de fusos horários. O seu caminho é determinado pela localização de um telescópio histórico, o “Airy Transit Circle” (51°28′40.1″N 0°0′5.3″W), que está localizado no Observatório Real de Greenwich, em Londres. O Meridiano de Greenwich foi criada por Sir George Airy em 1851.


The Prime Meridian in Greenwich Observatory, was long marked by a brass strip in the courtyard, now replaced by stainless steel, and, since 16 December 1999, has been marked by a powerful green laser shining north across the London night sky. The Meridian laser marks the route of the Greenwich Meridian by night in a northerly direction from the Royal Observatory. Under good viewing conditions, it is visible at a distance of over 36 miles with the naked eye and over 60 miles with binoculars.


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