because the Earth's axis is tilted by 23.5 degrees, it only allows the sun to be overhead at some time of the year in locations between the Tropic of Cancer (23.5 deg N) and the Tropic of Capricorn (23.5 deg S). The Arctic Circle is at 66.5 deg N, so the sun is never directly overhead at any time of the year
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Because of the sun rays are attracted by the EARTH AND SUN'S gravity and because earth is elliptical and tilt to 23.5 degree .