Greenwich Meridian

Greenwich Meridian, also called the prime meridian, the longitude line passing through the London country of Greenwich, labelled 0° longitude. Designated by an international conference in 1884 as the prime meridian, all other meridians of longitude are numbered east or west of it. The Greenwich Meridian is also the beginning of the earth's 24 time zones, each of which covers an area of 15° longitude.

See also: Longitude.