பயனர்:TNSE MANI VNR/மணல்தொட்டி: திருத்தங்களுக்கு இடையிலான வேறுபாடு
உள்ளடக்கம் நீக்கப்பட்டது உள்ளடக்கம் சேர்க்கப்பட்டது
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[[File:Polar-Night Longyearbyen.jpg|thumb|right|[[நோர்வே]] நாட்டில் 78° வடக்கில் அமைந்துள்ள [[சுவல்பார்டு]] என்ற இடத்திலுள்ள [[லாங்யியர்பியன்|லாங்யியர்பியனில்]] எடுக்கப்பட்ட நீல நிற அந்தி கருக்கலுள்ள துருவ இரவு.]]
[[File:Amundsen-Scott marsstation ray h.jpg|thumb|right|[[தென் துருவம்|தென் துருவத்திலுள்ள]] [[அந்தாட்டிக்கா]]வில் ஒரு துருவ இரவு.]]
[[File:Polar night in Naryan-Mar.jpg|thumbnail|right|[[உருசியா]]விலுள்ள நரியன்-மாரில் டிசம்பர் 23, 2014, 11:27 (நண்பகல்) எடுக்கப்பட்ட துருவ இரவு]]
'''துருவ இரவு''' ('''polar night''') என்பது [[புவி]]யின் [[தென் துருவம்]] மற்றும் [[வட துருவம்|வட துருவப்]] பகுதிகளில் 24 [[மணித்தியாலம்|மணி]] நேரத்தையும் தாண்டி இரவு நீடிப்பதை குறிப்பதாகும். இது துருவ வட்டங்களில் மட்டுமே நிகழும் ஒரு நிகழ்வாகும்.<ref>{{cite book|last=Burn|first=Chris|title=The Polar Night|url=http://nwtresearch.com/sites/default/files/the-polar-night.pdf|publisher=The Aurora Research Institute|accessdate=28 September 2015}}</ref>இதற்கு எதிரான செயலாக துருவப்பகல் அல்லது [[நள்ளிரவுச் சூரியன்]] கருதப்படுகிறது. இது [[ஞாயிறு (விண்மீன்)|ஞாயிறு ]] [[தொடுவானம்|தொடுவானத்திற்கு]] மேலே 24  மணி நேரமும் இருப்பதால் நிகழ்கிறது. இரவு என்பது சூரியன் தொடுவானத்திற்குக் கீழே செல்லும் போது நிகழ்கிறது. புவியின் வளி மண்டலம் சூரியக் கதிர்களை [[ஒளி முறிவு|ஒளி விலகல்]] அடையச் செய்வதால் துருவப்பகல் என்பது துருவ இரவை விட அதிகமாக இருக்கும். துருவ இரவு ஏற்படும் பகுதி துருவப்பகல் ஏற்படும் பகுதியை விட குறைவாகவே இருக்கும். 66.5 டிகிரி [[நிலநேர்க்கோடு|அட்சரேகை]] வரை துருவ வட்டம் பரவியிருக்கும். [[சுவீடன்]] நாட்டிலுள்ள [[கிருனா]] நகரே (67°51' வடக்கு) துருவ வட்டத்தின் வட முனையாகும். துருவ இரவு என்பது 28 மணி நேரம் வரை நீடிக்கும். ஆனால் நள்ளிரவுச் சூரியன் 50 மணி நேரம் வரை நீடித்திருக்கும். [[ஆர்க்டிக்]] பகுதியில் இரவாக இருக்கும் போது, [[அந்தாட்டிக்கா]] பகுதியில் பகலாக இருக்கும்.
[[நட்சத்திரம்|நட்சத்திரத்தைச்]] சுற்றி வரும் எந்ததொரு [[கோள்]] அல்லது [[துணைக்கோள்]] ஆகியவற்றின் [[அச்சுச் சாய்வு]] மற்றும் [[சுழற்சிக் காலம்]] அதன் [[சுற்றுக்காலம்|சுற்றுக்காலத்தை]] விட அதிகமாக இருக்கும் போது, இவ்வகை இரவு பகல் மாற்றங்கள் அனைத்து இடங்களிலும் நிகழும்.
==விளக்கம்==
The polar [[shortest day]] is not totally dark everywhere inside the polar circle, but only in places within about 5.5° of the poles, and only when the moon is well below the horizon. Regions located at the inner border of the polar circles experience polar [[twilight]] instead of polar night. In fact, [[polar region]]s typically get more twilight throughout the year than [[tropics|equatorial regions]].
For regions inside the polar circles, the maximum lengths of the time that the Sun is completely below the horizon varies from zero a quarter degree beyond the [[Arctic Circle]] and [[Antarctic Circle]] to 179 days at the [[Geographical pole|Poles]].{{citation needed|date=February 2011}} 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: the ellipticity of the Earth's orbit makes the South Pole receive a week more of Sun-below-horizon than the North Pole (see [[equinox]]).
== துருவ இரவின் வகைகள் ==
[[File:Morketidettermiddag.JPG|thumb|250px|right|Early afternoon during the polar night in [[Tromsø]], [[Norway]].]]
[[File:Nordkinnhalvoya-polar-night.jpg|thumb|right|250px|Polar night on [[Nordkinn Peninsula]] in Norway, mainland Europe's northernmost peninsula.]]
As there are various kinds of [[twilight]], there also exist various kinds of polar night. Each kind of polar night is defined as when it's darker than the corresponding kind of twilight. The descriptions below are based on relatively clear skies, so the sky will be darker in the presence of dense clouds.
===துருவ அந்தி===
Polar twilight occurs in areas that are located at the inner border of the polar circles, where the Sun will be on or below the horizon all day on the [[winter solstice]]. There is then no true [[daylight]] at the [[solar culmination]], only [[civil twilight]]. This means that the Sun is below the horizon, but by less than 6°. During civil twilight, there may still be enough light for normal outdoor activities because of light scattering by the upper atmosphere and refraction. [[Street lamp]]s may remain on and a person looking at a window from within a brightly lit room may see their reflection even at noon, as the level of outdoor [[illuminance]] will be below that of many illuminated indoor spaces.
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 night" for this purpose.
===குடிசார் துருவ இரவு===
The civil polar night period produces only a faint glow of light visible at midday. It happens when there is no [[civil twilight]] and only [[nautical twilight]] occurs at the [[solar culmination]]. Civil twilight happens when the Sun is between 0 and 6° below the horizon, and civil night when it is lower than that. Therefore, the civil polar night is limited to latitudes above 72° 34', which is exactly 6° inside the polar circle. Nowhere on mainland Europe is this definition met. On the Norwegian territory of [[Svalbard]], however, civil polar night lasts from about 11 November until 30 January. [[Dikson (urban-type settlement)|Dikson]], in Russia, experiences civil polar night for approximately a month. During dense cloud cover places like the coast of [[Finnmark]] (about 70°) in [[Norway]] will get a darker "day". On the Canadian territory of [[Pond Inlet, Nunavut]] however civil polar night lasts from about 16 December until 26 December.
=== கடல்சார் துருவ இரவு ===
During the nautical polar night period, there is no trace of daylight, except around midday. It happens when there is no [[nautical twilight]] and only [[astronomical twilight]] occurs at the [[solar culmination]]. Nautical twilight happens when the Sun is between six and twelve degrees below the horizon. There is a location at the [[horizon]] around midday with more light than others because of refraction. During nautical night, the Sun is lower than 12° below the horizon, so nautical polar night is limited to latitudes above 78° 34', which is exactly 12° within the polar circle, or 11.5° from the pole. [[Alert, Nunavut|Alert]], [[Nunavut]], the northernmost settlement in [[Canada]] and the world, experiences this from late November to mid-January.
On the Canadian territory of [[Eureka, Nunavut]] in [[Canada]] experiences this December 2 to January 8.
On the Norwegian territory of [[Svalbard]] Ny-Alesund experiences this mid to late December.
=== வானியல்சார் துருவ இரவு ===
The astronomical polar night is a period of continuous [[night]] where no [[astronomical twilight]] occurs. Astronomical twilight happens when the Sun is between twelve and eighteen degrees below the horizon and astronomical night when it is lower than that. Thus, the astronomical polar night is limited to latitudes above 84° 34', which is exactly 18° within the polar circle, or five and a half degrees from the pole. During the astronomical polar night stars of the sixth magnitude, which are the dimmest stars visible to the naked eye, will be visible throughout the entire [[day]]. This happens when the sun is between 18 and 23.5 degrees below the horizon. These conditions last about 11 weeks at the poles.
The [[Amundsen–Scott South Pole Station]] experiences this from May 15 to late July.
The North Pole experiences this from November 14 to January 29.<ref name="arctic polar night livescience">{{cite web|last1=Rao|first1=Joe|title=The Myth of Arctic Daylight and Darkness Exposed|url=http://www.livescience.com/32814-arctic-daylight-darkness-myth-equinox.html|website=[[Live Science]]|accessdate=14 April 2017|date=21 September 2010}}</ref>
=== துருவ சூரியச் சுற்று ===
If an observer located on either the North Pole or the South Pole were to define a "day" as the time from the maximal elevation of the Sun above the horizon during one period of daylight, until the maximal elevation of the Sun above the horizon of the next period of daylight, then a "polar-day" as experienced by such an observer would be one Earth-year long.<ref>[https://www-istp.gsfc.nasa.gov/stargaze/StarFAQ10.htm#q164 NASA: The Sun and Seasons] NASA. (See last paragraph, section 164.) By David Stern. Last updated Sept. 17, 2004. Downloaded Feb. 17, 2017.</ref>
==பரவலான கலாச்சாரத்தில்==
The concept of a night of almost one month in length has been the subject of the vampire movies ''[[Frostbite (2006 film)|Frostbite]]'' and ''[[30 Days of Night (film)|30 Days of Night]]''. In these films, the vampires are drawn to the long duration of darkness, allowing them to openly kill and feed at will.
==மேற்கோள்கள்==
{{
==மேலும் படிக்க==
* {{cite journal
| last1 = Hansen
| first1 = V.
| last2 = Lund
| first2 = E.
| last3 = Smith-Sivertsen
| first3 = T.
|date=March 1998
| title = Self-reported mental distress under the shifting daylight in the high north
| journal = [[Psychological Medicine]]
| volume = 28
| issue = 2
| pages = 447–452
| doi = 10.1017/S0033291797006326
| pmid=9572101
}}
==வெளியிணைப்புகள்==
* [https://web.archive.org/web/20120904173515/http://collections.ic.gc.ca/simply_science/toc.htm The polar night and polar darkness]
* [http://weather.cs.uit.no/video/index-2006.html Many years' of webcam pictures from Tromsø, Norway.] These clearly show the progression into and away from winter at a latitude within the Arctic Circle.
[[Category:Earth phenomena]]
[[Category:Arctic geography terminology]]
[[Category:Night]]
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