The New Student's Reference Work/Zone

Zone, literally a belt or girdle, a portion of the surface of a globe or sphere lying between any two circles of the same whose planes are parallel to each other, or that portion of the surface of a sphere cut off by the plane of a circle. As the earth's axis is inclined 23½° to the plane of the ecliptic or the sun's apparent path around the earth, the tropics of Cancer and Capricorn are located that distance north and south of the equator, respectively; and for the same reason the Arctic Circle and the Antarctic Circle are located 23½° from the north and south poles respectively. These circles are accordingly said to divide the earth's surface into five zones: to wit, the North Frigid, lying north of the Arctic Circle; the North Temperate, lying between the Arctic Circle and the Tropic of Cancer; the Torrid, lying on both sides of the equator, between the Tropic of Cancer on the north and the Tropic of Capricorn on the south; the South Temperate, lying between the Tropic of Capricorn and the Antarctic Circle; and the South Frigid, lying south of the Antarctic Circle. The area of a zone on any sphere is equal to the circumference of a great circle multiplied by the height of the zone.