There are 180 degrees of longitude between the Prime Meridian and the International Date Line. The Prime Meridian is defined as 0° longitude, running through Greenwich, England, and it divides Earth into the eastern and western hemispheres. The International Date Line is based on the antimeridian at 180° longitude, roughly opposite the Prime Meridian on the globe. Since longitude is measured in degrees around a full 360° circle, the point exactly halfway around from 0° is 180°, so the angular distance between the Prime Meridian and the International Date Line is 180° of longitude.