http://en.wikipedia.org/wiki/Arctic_Circle
what is the artic circle?
what is the line of cancer and capricorn?
The Arctic Circle is one of the five major circles of latitude on Earth. It is an imaginary boundary line that circles the northern hemisphere at approximately 66.5 degrees north of the equator. The line marks the southernmost point at which the sun remains visible for a continuous 24 hours during the summer solstice, usually around June 21st. Conversely, during the winter solstice around December 21st, the Arctic Circle marks the boundary within which the sun remains below the horizon continuously for a full 24 hours.
The "line of Cancer and Capricorn" refers to the Tropic of Cancer and the Tropic of Capricorn, respectively. These are the two major circles of latitude located at approximately 23.5 degrees north and south of the equator. The Tropic of Cancer is the northernmost point at which the sun appears directly overhead at noon during the summer solstice in the Northern Hemisphere, while the Tropic of Capricorn is the southernmost point where this occurs during the summer solstice in the Southern Hemisphere. These tropics mark the boundaries within which the sun can be directly overhead at least once a year.