III.

Degree of Longitude

The length of a degree of longitude varies from a maximum value at the equator to zero at the North and South poles. This is because longitude is measured as the arc of a given parallel of latitude, and the circles forming these parallels decrease in radius as their distance from the equator increases. At the equator a degree of longitude equals 112.09 km (69.65 mi), but at 40° North or South, a degree equals 85.99 km (53.43 mi). Longitude is also measured in hours east or west of the prime meridian, with an hour equal to 15 degrees and a minute, to 15 angular minutes. Thus, the longitude of New York City may be stated as 74° or as 4 hr 56 min west of Greenwich. See also Latitude and Longitude.