Meridian is a line drawn from the North Pole to the South Pole on a globe. Each line goes halfway around the globe and meets another line at both poles. Two meridians that meet at the poles form a meridian circle.
People use meridian lines to measure longitude, the distance east or west of a line passing through Greenwich, a borough of London. That line is known as the prime meridian, and its longitude is 0°. There are meridians all the way around the globe, and so there are 360° of longitude—180° of east longitude and 180° of west longitude.
At the equator, the distance between points that are 1° apart is about 69 miles (111 kilometers). This distance becomes smaller as the lines converge, eventually meeting at the poles. In 24 hours, Earth rotates 360° on its axis, so the planet turns 15° per hour. Thus, time zones are 15° of longitude wide.
See also Greenwich meridian ; International date line ; Longitude ; Map ; Standard time .
