Friday, December 19, 2014

The Prime Meridian At The Royal Observatory, Greenwich

The Prime Meridian, also known as the Greenwich Meridian, passes through longitude 0° 0' 0'' and on its journey from pole to pole, it passes through England, France, Spain, Algeria, Mali, Burkina Faso, Togo, Ghana and Antarctica, dividing the earth into east and west, just as the Equator splits it into north and south. The meridian’s position is marked in hundreds of places, but the best place to see this all important imaginary line is in Greenwich Park in London. The marker is located at the Royal Observatory, a former observatory and now a museum, that played a major role in the history of astronomy and navigation. Its path is determined by the location of a historic telescope, the Airy Transit Circle, which is housed at the observatory’s premises.

The Royal Observatory was established in 1675, and since then the British astronomers have used it as a basis for astronomical measurement. In 1851, the astronomer Sir George Biddell Airy built an instrument called the transit circle for timing the passage of stars across the local meridian, and in doing so established the location of the Prime Meridian. Three years later, in 1884, the Prime Meridian was adopted, by an international decree, as the official zero-degree longitude. To mark the line, a brass strip was laid down across the courtyard, which was later upgraded to stainless steel. In December 1999, an additional marker was installed – a powerful green laser that shines north across the London night sky.














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