Circle Arctic

Circle, Arctic, is a circle round the north pole at the uniform angular distance of 23-1/2°. It, therefore, is identical with the line of north latitude 66-1/2°. It separates the Arctic from the North Temperate zone, just as in the southern hemisphere the Antarctic circle separates the Antarctic from the South Temperate zone. Inasmuch as 23-1/2° is the angle of obliquity of the earth's equator to the ecliptic, there are periods of the year when the sun never sets during the day, and other periods when it never rises during the day, in the Arctic and Antarctic regions.