The line which marks approximately the northernmost place in the Southern Hemisphere where the sun does not set on the summer solstice and does not rise on the winter solstice
The line of latitude 6634S (often taken as 66S) Along this line the sun does not set on the day of the summer solstice, about 22 December, and does not rise on the day of the winter solstice, about 21 June
an imaginary line around the world at a particular distance from the most southern point, which is the South Pole Arctic Circle. Parallel of latitude approximately
5° south of the Equator that circumscribes the southern frigid zone. It marks the northern limit of the area within which, for one day or more each year, the sun does not set or rise. The length of continuous day or night increases southward from the Antarctic Circle, mounting to six months at the South Pole