Polar Night - Description

Description

A common misconception is that the shortest day is totally dark at each point where the midnight sun occurs inside the polar circle. In places very close to the poles this is true, but in regions that are located at the inner border of the polar circles where the midnight sun is experienced, this is not the case. Because of twilight, these regions experience polar twilight instead of the polar night. In fact, polar regions typically get more twilight throughout the year than equatorial regions.

For regions inside the polar circles, the maximum lengths of the time that the sun is completely below the horizon varies from about 20 hours at the Arctic Circle and Antarctic Circle to 179 days at the Poles. However not all this time is classified as polar night, since sunlight may be visible because of refraction. Also, the time when the sun is above the horizon at the poles is 186 days. The numerical asymmetry occurs because the time when the sun is partially above the horizon is counted towards the "daytime". Also, the above numbers are average numbers: owing to the ellipticity of the Earth's orbit, where the South pole receives a week more of sun-below-horizon than the North pole (see equinox).

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