Portal:Antarctica/Selected article/4
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Polar night is a phenomenon resulting from the axial tilt of the Earth respective to the Sun, where the Sun does not rise above the horizon during any 24 hour period in the regions of the Earth in proximity to the poles . The length of this time when the sun is constantly below the horizon varies from 20 hours at locations on the Arctic Circle and Antarctic Circle to 179 days at the geographic poles. The period of polar night can trigger depression in some people. People who suffer from seasonal affective disorder are particularly susceptible.
