Figure GT.19

Longitude and meridians. (A) Longitude is determined by the angular distance from the prime meridian, which runs through Greenwich, England. Traveling east from the prime meridian, we pass through the Eastern Hemisphere, which ends at 180 degrees. Traveling west from the prime meridian, we pass through the Western Hemisphere, which also ends at 180 degrees. (B) Meridians are lines created by connecting points of longitude. The prime meridian (0 degrees longitude) and a portion of the 180th meridian (180 degrees longitude) are shown. All meridians terminate at the poles.