The Royal Greenwich ObservatoryGreenwich and the Royal Greenwich Observatory (RGO) have a special place in the hearts of horologists. The original RGO is the location of the prime meridian, the basis from which Greenwich Mean Time (GMT) is calculated. Greenwich could justifiably be called the "home of time".
The Royal Greenwich Observatory was commissioned by King Charles II in 1675 as a workplace for the astronomer royal. It was sighted on a hill in Greenwich park, overlooking the river Thames. The first astronomer royal was John Flamstead, his successor was Edmund Halley of comet fame.
One of the main purposes of the RGO was to assist in navigation at sea and in attempting to solve the problem of longitude. The reward for solving this problem eventually went to watchmaker John Harrison for his famous H4 watch. Harrison's watches are preserved in the Harrison Gallery of the observatory.
Although the site of the Royal Greenwich Observatory is a popular tourist attraction, the RGO as such is no longer operational. Growing light pollution from London resulted in the observatory proper being relocated to Hurstmonceux Castle in Sussex in 1948. In 1988 it was relocated again to Cambridge before being merged with the Royal Observatory Edinburgh in 1998. The original Greenwich site is now part of the National Maritime Museum.
A popular feature of the Observatory site is the prime meridian line. This metal strip set is set into the courtyard and marks precisely zero degrees longitude. Tourists frequently have themselves photographed straddling this line - one foot in the East, the other in the West.
Another popular atraction for tourists is the 1PM ball. This time ball was installed by Astronomer Royal John Pond in 1833 and provides a precise visual indication of 1PM GMT. At five minutes before one each day the ball begins rising to the top of a pole, then at precisely 13:00 it drops. Given the location of the observatory, the time ball could be seen by ships on the river Thames and was used by them to set their chronometers.
National Maritime Museum