Polar night: Difference between revisions
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In regions inside the polar circles, the sun does not rise above the horizon for one or more days. |
In regions inside the polar circles, the sun does not rise above the horizon for one or more days. |
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== Civil polar night == |
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The ''civil polar night'' is period during which no [[civil twilight]] occurs. Civil twilight happens when the sun is between zero and six degrees below the horizon. Because of [[refraction]], there still is enough [[light]] for normal outdoor activities. Civil polar night is limited to regions inside 72 ° 33', which is exactly six degrees inside the plor circle. In mainland [[Europe]], there are no places fulfilling this definition. |
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== Nautical polar night == |
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| ⚫ | The ''nautical polar night'' is the period during which there is only a faint glow of light visible during [[midday]]. It happens when there is no [[nautical twilight]]. Nautical twilight happens when the sun is between six and twelve degrees below the horizon. Because of [[refraction]], there is still a place at the [[horizon]] with clearly more light than other places. The nautical polar night is limited to regions inside 78 ° 33 ', which is exactly 12 degrees within the polar circle. |
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== Astronomical polar night == |
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== See also == |
== See also == |
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Revision as of 08:51, 25 October 2004
The polar night is the night lasting more than 24 hours, usually inside the polar circles. Various different kinds of polar night exist. A common misunderstanding is that at each point inside the polar circle, or each place where midnight sun occurs, the shortest day is totally dark. Because of twilight, this is not the case. In fact, polar regions get more light throughout the year than regions located closer to the equator. For example, during seven months, Kiruna at 67° 49' N, (slightly north the arctic circle) has more light than Stockholm at 59° 39' N.
In regions inside the polar circles, the sun does not rise above the horizon for one or more days.
Civil polar night
The civil polar night is period during which no civil twilight occurs. Civil twilight happens when the sun is between zero and six degrees below the horizon. Because of refraction, there still is enough light for normal outdoor activities. Civil polar night is limited to regions inside 72 ° 33', which is exactly six degrees inside the plor circle. In mainland Europe, there are no places fulfilling this definition.
Nautical polar night
The nautical polar night is the period during which there is only a faint glow of light visible during midday. It happens when there is no nautical twilight. Nautical twilight happens when the sun is between six and twelve degrees below the horizon. Because of refraction, there is still a place at the horizon with clearly more light than other places. The nautical polar night is limited to regions inside 78 ° 33 ', which is exactly 12 degrees within the polar circle.
Astronomical polar night
Finally, the astronomical polar night is the period that no trace of light can be seen anywhere and no astronomical twilight occurs. It happens inside 84 ° 33', which is exactly 16 degrees within the polar circle.