- an imaginary line drawn parallel to the equator, at 23°28prime; S of the North Pole: between the North Frigid Zone and the North Temperate Zone.
- the imaginary circle round the earth, parallel to the equator, at latitude 66° 32′ N; it marks the northernmost point at which the sun appears above the level of the horizon on the winter solstice
1550s, in reference to a celestial circle, a line around the sky which, in any location, bounds the stars which are ever-visible from that latitude (in the Northern Hemisphere, this is focused on the celestial north pole); the concept goes back to the ancient Greeks, for whom this set of constellations included most prominently the two bears (arktoi), hence the name for the circle (see ). Of Earth, the circle 66 degrees 32 minutes north of the equator, marking the southern extremity of the polar day, it is recorded from 1620s.
- The parallel of latitude approximately 66°33′ north. It forms the boundary between the North Temperate and North Frigid zones.
Imaginary circle around theabout three-quarters of the way from the to the . North of this line is the “Land of the Midnight Sun,” where the sun never sets on the summer .