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Polar night
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==Types of polar night== {{More citations needed section|date=October 2022}} [[File:Morketidettermiddag.JPG|thumb|right|Early afternoon during civil polar twilight in [[Tromsø (city)|Tromsø]], [[Norway]].]] [[File:Nordkinnhalvoya-polar-night.jpg|thumb|right|Civil polar twilight on [[Nordkinn Peninsula]] in Norway, mainland Europe's northernmost peninsula.]] ===Polar twilight=== As mentioned, a location experiencing polar night does not mean that the location will be in full darkness; in most cases, due to sunlight being [[Refraction|refracted]] over the horizon, a location experiencing polar night will actually be in one of the various phases of polar twilight. As in locations experiencing daylight, the middle of the day will typically be the brightest time in locations experiencing polar twilight.<ref>{{Cite web |last=Mulvaney |first=Kieran |date=2024-02-01 |title=What is polar night? |url=https://www.nationalgeographic.com/environment/article/polar-night-arctic-antarctic |access-date=2024-02-28 |website=Environment |language=en}}</ref> For example, a typical day during civil polar twilight in [[Vadsø Municipality|Vadsø, Norway]] will begin with night, astronomical twilight, nautical twilight, and civil twilight in that order (with each successive phase including more light than the last). Following civil twilight, the day will progress through the other phases in the opposite order (nautical twilight, then astronomical twilight, then night to end the day).<ref>{{Cite web |date=2023-01-12 |title=The Polar Night and the Polar Day - Aurora Labs Norway |url=https://auroralabsnorway.com/the-polar-night-and-the-polar-day/ |access-date=2024-03-07 |language=en-US}}</ref> ====Civil polar twilight==== Civil polar twilight occurs at latitudes above 72°34' North or South, where the Sun will be below the horizon all day on the [[winter solstice]], but by less than 6° at [[solar noon]].<ref>{{cite web |url=https://basecampexplorer.com/spitsbergen/arctic-dictionary/polar-night/ |title=Polar Night|author=<!--Not stated--> |date= |website=Base Camp Explorer |publisher= |access-date=February 6, 2025}}</ref> There is then no true [[daylight]] at the [[solar culmination]], only [[civil twilight]]. During civil polar twilight, there is still enough light for most normal outdoor activities at midday because of light scattering by the upper atmosphere and refraction. However, during dense cloud cover, places like the coast of [[Finnmark]] (about 70°) in [[Norway]] will experience a "day" that is darker than usual. [[Street lamp]]s may therefore remain on even at midday, and a person looking at a window from within a brightly lit room might still be able to see their reflection, as the level of outdoor [[illuminance]] will be below that of many illuminated indoor spaces. Northern Hemisphere: *68° North: about December 9 to January 2 *69° North: about December 1 to January 10 *70° North: about November 26 to January 16 *71° North: about November 21 to January 21 *72° North: about November 16 to January 25 Southern Hemisphere: *68° South: about June 7 to July 3 *69° South: about May 30 to July 11 *70° South: about May 24 to July 18 *71° South: about May 19 to July 23 *72° South: about May 14 to July 27 Sufferers of [[seasonal affective disorder]] tend to seek out therapy with artificial light, as the psychological benefits of daylight require relatively high levels of ambient light (up to 10,000 [[lux]]) which are not present in any stage of twilight; thus, the midday twilights experienced anywhere inside the polar circles are still "polar nights" for this purpose. ====Nautical polar twilight==== Nautical polar twilight occurs at latitudes between about 72° 34' and 78° 34' North or South, which is exactly 6° to 12° inside the polar circles. There is then no [[civil twilight]] at the [[solar culmination]], only [[nautical twilight]]. During nautical polar twilight, the human eye may distinguish general outlines of ground objects at midday but cannot participate in detailed outdoor operations.<ref>{{Cite web |url=http://aa.usno.navy.mil/faq/docs/RST_defs.php |title=Rise, Set, and Twilight Definitions |access-date=2007-09-06 |archive-date=2015-08-14 |archive-url=https://web.archive.org/web/20150814180458/http://aa.usno.navy.mil/faq/docs/RST_defs.php |url-status=dead }}</ref> Civil twilight happens when the Sun is between 0 and 6° below the horizon, so this phenomenon can also be referred to as civil polar night. Nowhere on mainland Europe is this definition met. The Norwegian town of [[Longyearbyen]], [[Svalbard]], experiences nautical polar twilight from about 11 November until 30 January. [[Dikson (urban-type settlement)|Dikson]], in Russia, experiences nautical polar twilight from about 6 December to 6 January. On the Canadian territory of [[Pond Inlet, Nunavut]], nautical polar twilight lasts from about 16 December until 26 December. ====Astronomical polar twilight==== Astronomical polar twilight occurs at latitudes between about 78° 34' and 84° 34' North or South, which is exactly 12° to 18° inside the polar circles. There is then no [[nautical twilight]] at the [[solar culmination]], only [[astronomical twilight]]. During astronomical polar twilight, the sky is dark enough at midday to permit astronomical observation of point sources of light such as [[star]]s, except in regions with more intense [[skyglow]] due to [[light pollution]], [[moonlight]], [[aurora]]s, and other sources of light. There is a location at the [[horizon]] with more light than others around midday due to refraction. Some critical observations, such as of faint diffuse items such as [[nebula]]e and [[galaxy|galaxies]], may require observations beyond the limit of astronomical twilight. Nautical twilight happens when the Sun is between 6 and 12° degrees below the horizon, so this phenomenon can also be referred to as nautical polar night. The Norwegian town of [[Ny-Ålesund]], [[Svalbard]], experiences this from about December 12 to 30. Its antipode ({{coord|78|55|S|168|4|W}}) experiences this from about June 12 to July 1. The [[Canada|Canadian]] research base of [[Eureka, Nunavut]], experiences this from about December 2 to January 8. Its antipode ({{coord|79|59|S|94|4|E}}) experiences this from about June 1 to July 11.<ref>{{Cite web |title=Time and Date.com - Eureka, Nunavut, Canada |url=https://www.timeanddate.com/sun/canada/eureka |access-date=March 26, 2024 |publisher=Time and Date.com}}</ref> The Russian territory of [[Franz Josef Land]] experiences this from about November 27 to January 15. Its antipode ({{coord|81|S|125|W}}) experiences this from about May 25 to July 17. [[Alert, Nunavut|Alert]], [[Nunavut]], the northernmost settlement in [[Canada]] and the world, experiences this from about November 19 to January 22. Its antipode ({{coord|82|30|S|117|38|E}}) experiences this from about May 19 to July 25.<ref>{{Cite web |title=Time and Date.com - Alert, Nunavut, Canada |url=http://www.timeanddate.com/sun/canada/alert |access-date=May 14, 2019 |publisher=Time and Date.com}}</ref> [[Oodaaq]], a gravel bank at the northern tip of [[Greenland]] and a disputed [[northernmost point of land]], experiences this from about November 15 to January 27. Its antipode ({{coord|83|40|S|150|7|E}}) experiences this from about May 13 to July 31.<ref>{{Cite web |title=Time and Date.com - Oodap Qeqertaa, Greenland |url=https://www.timeanddate.com/sun/@3426180 |access-date=May 16, 2019 |publisher=Time and Date.com}}</ref> ===True polar night=== A true polar night is a period of continuous [[night]] where no [[astronomical twilight]] occurs at the [[solar culmination]]. During a true polar night, stars of the sixth magnitude, which are the dimmest stars visible to the naked eye, will be visible throughout the entire 24-hour [[day]]. At [[solar noon]], the sun will be between exactly 18° and approximately 23° 26' below the horizon. These conditions last for about 11 weeks at the poles. Astronomical twilight happens when the Sun is between 12 and 18° degrees below the horizon, so this phenomenon can also be referred to as astronomical polar night. True polar night is limited to latitudes above roughly 84° 34' North or South, which is exactly 18° within the polar circles, or approximately five and a half degrees from the poles. The only permanent settlement on Earth at these latitudes is the [[Amundsen–Scott South Pole Station|Amundsen–Scott scientific research station]] in [[Antarctica]], whose winter personnel are completely isolated from mid-February to late October. The [[South Pole]] experiences this from about May 11 to August 1,<ref>{{Cite web |title=Time and Date.com - South Pole, Antarctica |url=https://www.timeanddate.com/sun/antarctica/south-pole |access-date=June 1, 2019 |publisher=Time and Date.com}}</ref> while the [[North Pole]] experiences this from about November 12 to January 28.<ref name="arctic polar night livescience">{{Cite web |last=Rao |first=Joe |date=21 September 2010 |title=The Myth of Arctic Daylight and Darkness Exposed |url=http://www.livescience.com/32814-arctic-daylight-darkness-myth-equinox.html |access-date=14 April 2017 |website=[[Live Science]]}}</ref><ref>{{Cite web |title=Time and Date.com - North Pole |url=https://www.timeanddate.com/sun/@90.0000000,0.0000000 |access-date=March 12, 2024 |publisher=Time and Date.com}}</ref>
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