Polar night

The polar night is the night lasting more than 24 hours, usually inside the polar circlespolar circle: koło podbiegunowe. Various kinds of polar night exist. A common misunderstanding is that at each point inside the polar circle, or each place where midnight sunsłońce widziane w środku nocy, o północy occurs, the shortest day is totally dark. Because of twilightpółrok, zmierzch, brzask, świt, this is not the case. In fact, polar regions get more light throughout the year than regions located closer to the equatorrównik. For example, during seven months, Kiruna at 67° 49' N, (slightly north the Arctic Circle) has more light than Stockholm at 59° 39' N. The opposite phenomenon, when the sun stays above the horizon for a long time is called the polar day or midnight sunsłońce widziane w środku nocy, o północy.

In regions inside the polar circlespolar circle: koło podbiegunowe, the length of the time when the sun is below the horizon varies from 20 hours at the Arctic Circle and Antarctic Circle to 179 days at the PolesPole: Biegun. However not all this time is classified as polar night, since there may be plenty of sunlight because of refractionzałamanie, refrakcja. Also, one might notice that the time above the horizon at the poles is said to be 186 days. The asymmetry in numbers is because the time when the sun is partially above the horizon is counted towards the "daytime".

Civil polar night
The civilcywilny, obywatelski, domowy polar night is period during which no civilcywilny, obywatelski, domowy twilightpółrok, zmierzch, brzask, świt occurs. Civil twilightpółrok, zmierzch, brzask, świt happens when the sun is between zero and six degrees below the horizon. Because of refractionzałamanie, refrakcja, there still is enough light for normal outdoor activities. Civil polar night is limitedograniczony to regions inside 72° 33', which is exactly six degrees inside the polar circle. In mainlandkontynent, ląd stały Europe, there are no places fulfilling this definition.

Nautical polar night
The nauticalmorski, żeglarski polar night is the period during which there is only a faintsłaby, lekki glowblask, żar, łuna of light visible during midday. It happens when there is no nauticalmorski, żeglarski twilightpółrok, zmierzch, brzask, świt. Nautical twilightpółrok, zmierzch, brzask, świt happens when the sun is between six and twelve degrees below the horizon. Because of refractionzałamanie, refrakcja, there is still a place at the horizon with clearly more light than other places. The nauticalmorski, żeglarski polar night is limitedograniczony 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 traceślad, znak of light can be seen anywhere and no astronomical twilightpółrok, zmierzch, brzask, świt occurs. It happens inside 84° 33', which is exactly 16 degrees within the polar circle.

Effects on humans
The period of polar night is reportedlywedług na podstawie doniesień, prawdopodobnie, rzekomo very taxingtrudny, skomplikowany on the human body and can triggerwywoływać, powodować, inicjować depression in many people. Polar days affect people as well. People who suffer from seasonal affective disorder are particularly susceptiblepodatny, wrażliwy.

Url źródłowy: http://en.wikipedia.org/wiki/Polar_night

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