Longitude

Longitude describes the location of a place east? or west? of a north-south line called the [prime meridian]?. Longitude is an [angular measurement]? ranging from 0° at the [prime meridian]? to plus or minus 180°. Zero degrees is defined as a point which passes through Greenwich in London, England.

This measurement is important to navigation; the discovery of how to measure it accurately was one of the more important discoveries of the 1700?s. See Dava Sobel's book " : The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time" for a good historical overview. This genius was John Harrison who eventually received the Longitude Prize.

See latitude.