longitude - an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator; "all points on the same meridian have the same longitude"great circle - a circular line on the surface of a sphere formed by intersecting it with a plane passing through the center prime meridian - meridian at zero degree longitude from which east and west are reckoned (usually the Greenwich longitude in England) magnetic meridian - an imaginary line passing through both magnetic poles of the Earth |