Why are the Arctic and Antarctic circles specifically located at 66°30' north and 66°30' south?
by 
wickedwillie
ANSWERS: 2
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The Arctic Circle is the imaginary circle on the surface of the earth at 661/2°N latitude, i.e., 231/2° south of the North Pole. It marks the northernmost point at which the sun can be seen at the winter solstice (about Dec. 22) and the southernmost point of the northern polar regions at which the midnight sun is visible. The Antarctic Circle is the imaginary circle on the surface of the earth at 661/2°S lat., i.e., 231/2° north of the South Pole. It marks the southernmost point at which the sun can be seen at the winter solstice (about June 22) and the northernmost point of the southern polar regions at which the midnight sun is visible.
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allbyend's answer gives good information about the characteristics of the polar circles but really doesn't answer the question of why they are where they are. The reason that the polar circles are where they are is because Earth's axis of rotation is tilted at an angle of 23.5° off perpendicular to the plane of its orbit. Because of this tilt, the tropics are at 23.5° north and south latitude and the polar circles are at 66.5° (90.0° - 23.5°).
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