The polar night occurs in the northernmost and most southerly regions of the earth when the night lasts for more than 24 hours. This only happens inside the polar circle. The opposite phenomenon, polar day, or midnight sun, occurs when the Sun is above the horizon for more than 24 hours. "Night" is understood as the center of the Sun is under the free horizon. Because the atmosphere bends the sun, polar day is longer than polar night, and the area affected by the polar night is somewhat smaller than the midnight sun area. The polar circle lies at the latitude between these two areas, at a latitude of about 66.5 degrees. In Sweden's northernmost city, Kiruna, at 67 Â ° 51'N, the polar night lasts for about 28 twenty-four hours, while the midnight sun lasts about 50 twenty-four hour periods. As for the day in the Arctic Circle, this is the night in the Antarctic Circle.
Any planet or moon with a sufficient axis that rotates to its star significantly more often than orbiting a star (there is no tidal locking between the two) will experience the same phenomenon (night time lasting more than one rotation period).
Video Polar night
Description
The shortest day of polar is not completely dark everywhere inside the polar circle, but only in places within about 5.5 ° of the poles, and only when the moon is far below the horizon. The region lying on the inner border of the polar circle experiences the polar twilight instead of the polar night. In fact, the polar regions usually get more twilight throughout the year than the equatorial region.
For areas within the polar circle, the maximum length of time the Sun is entirely below the horizon varies from zero to a quarter degrees outside the Arctic Circle and the Antarctic Circle up to 179 days at the Pole. However, not all of these times are classified as polar nights because sunlight may be seen due to refraction. Also, the time when the Sun is above the horizon at the poles is 186 days. Numerical asymmetry occurs because the time when the Sun is partially above the horizon is calculated toward daylight. Also, the above figures are the average number: Earth's ellipticity orbit makes the South Pole receive a week more than the Sun under the horizon rather than the North Pole (see equinox).
Maps Polar night
Polar night type
Because there are various kinds of twilight, there are also various types of polar night. Each polar night type is defined as the darker time of the corresponding twilight. The description below is based on a relatively clear sky, so the sky will be darker in the presence of thick clouds.
Polar twilight
Polar twilight occurs in an area located on the inner border of the polar circle, where the Sun will be at or below the horizon throughout the day at the winter solstice. No noon is right at the top of the sun, just civil twilight. This means that the Sun is below the horizon, but less than 6 Â °. During the civilian twilight, there may still be enough light for normal outdoor activities due to light scattering by the upper atmosphere and refraction. The streetlights may remain lit and someone who sees the window from a bright room can see their reflections even during the day, as the level of outdoor lighting will be under a lot of illuminated inner space.
Suffering from seasonal affective disorder tends to seek therapy with artificial light, since the psychological benefits of daylight require relatively high levels of ambient light (up to 10,000 lux) that are absent at every stage of the twilight, so, at noon dusk experience anywhere within the polar circle still "polar night" for this purpose.
Civic Polar Night
The civil polar period of night produces only the faint glow seen at midday. It happens when there is no civilian twilight and only the dusk of the sea that takes place at the top of the sun. Civilian twilight occurs when the Sun is between 0 and 6 Â ° below the horizon, and civil night when it is lower than that. Therefore, the civil pole's night is confined to latitude above 72 ° 34 ', the exact 6 ° in the polar circle. There is no place in mainland Europe that meets this definition. In the Norwegian region of Svalbard, however, the civilian polar night lasts from about 11 November to 30 January. Dikson, in Russia, experienced a civil polar night for approximately one month. During solid clouds covering places like Finnmark beach (about 70 °) in Norway will get a darker "day". In the Canadian region of Pond Inlet, Nunavut but the polar civil night lasts from around December 16 to December 26.
Polar night night
During the polar night period, there is no trace of daylight, except around noon. It happens when there is no sunset and only the dusk of astronomy takes place at the top of the sun. Twilight occurs when the Sun is between six and twelve degrees below the horizon. There is a location on the horizon around noon with more light than others due to refraction. During the nautical night, the Sun is lower than 12 Â ° below the horizon, so the polar sea night is confined to latitude above 78 ° 34 ', the exact 12 Â ° in the polar circle, or 11.5 Â ° from the poles. Warning, Nunavut, the northernmost settlement in Canada and the world, experienced this from late November to mid-January.
In the Canadian region of Eureka, Nunavut in Canada is from 2 December to 8 January.
Norway's Svalbard Ny-Alesund is in mid to late December.
Astronomical polar night
The astronomical polar night is a continuous night period in which no astronomical dusk takes place. Dusk astronomy occurs when the Sun is between twelve and eighteen degrees below the horizon and the night of astronomy when it is lower than that. Thus, the astronomical polar night is confined to a latitude above 84 ° 34 ', exactly 18 ° in a polar circle, or five and a half degrees from the poles. During the night stars the astronomical pole of the sixth magnitude, which is the dimest star visible to the naked eye, will be visible throughout the day. This occurs when the sun is between 18 and 23.5 degrees below the horizon. This condition lasts about 11 weeks at the poles.
South Amandsen-Scott Police Station experienced this from May 15 until the end of July.
The North Pole experiences this from November 14 to January 29.
Polar Sun cycle
If an observer located in the Arctic or South Pole should define "day" as the time from the maximum height of the Sun above the horizon during one daytime period, to the maximum height of the Sun above the horizon of the next daytime period, then "polar-day" experienced by such an observer will be a year of Earth.
In popular culture
The concept of a nearly one-month long night has been the subject of the vampire movie Frostbite and 30 Days of Night. In these movies, vampires are attracted to the long duration of darkness, allowing them to kill and feed openly.
References
Further reading
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Hansen, V.; Lund, E.; Smith-Sivertsen, T. (March 1998). "Self-reported mental difficulties under a high daytime shift in the north". Psychological Medicine . 28 (2): 447-452. doi: 10.1017/S0033291797006326. PMID 9572101.
External links
- Polar and polar nights
- Years of webcam images from TromsÃÆ'¸, Norway. This clearly shows the progression into and away from winter at the latitudes within the Arctic Circle.
Source of the article : Wikipedia
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