In geography and astronomy, length; the angular distance east or west of the prime meridian that stretches from the north pole to the south pole and passes through Greenwich, England: Longitude is measured in degrees, minutes, and seconds.

The angular distance in degrees that a celestial object lies east or west of Greenwich Meridian, or the meridian passing through Greenwich (Greater London borough on the Thames in England: The geocentric longitude was internationally adopted as the Earth's zero of longitude in 1884.