The Greenwich Meridian line is the centre of the world time. It runs through greenwich, England and is at 0 degrees longitude. The Royal Observatory in Greenwich is the home of Greenwich Mean Time (GMT) and the Prime Meridian of the world. For many years, different countries measured longitude from different meridians. From pole to pole, the Prime Meridian covers a distance of 20,000 km.
British astronomers have long used the Royal Observatory as a basis for measurement: four separate meridians have been drawn through the building. The basis of longitude, the Prime Meridian, established in 1851 and adopted at an international conference in 1884, passes through the Airy transit circle of the observatory. It was long marked by a brass strip in the courtyard, now upgraded to stainless steel, and, since 16 December 1999, has been marked by a powerful green laser shining north across the London night sky.
British astronomers have long used the Royal Observatory as a basis for measurement: four separate meridians have been drawn through the building. The basis of longitude, the Prime Meridian, established in 1851 and adopted at an international conference in 1884, passes through the Airy transit circle of the observatory. It was long marked by a brass strip in the courtyard, now upgraded to stainless steel, and, since 16 December 1999, has been marked by a powerful green laser shining north across the London night sky.