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{{Short description|Convection cell in the Sun's photosphere}} |
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{{Other uses|Granule (disambiguation)}} |
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[[File:Highest_resolution_photo_of_Sun_(NSF)_as_of_January_20,_2020.jpg|thumb|High-resolution image of the Sun's surface taken by the [[Daniel K. Inouye Solar Telescope]] (DKIST).]] |
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[[File:Granules2-Cropped-Photospheric-Granulation-G.Scharmer-Swedish-Vacuum-Solar-Telescope-10-July-1997.jpg|thumb|260px|Solar photosphere, with North America superimposed for scale.]] |
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In [[solar physics]] and [[Solar observation|observation]], '''granules''' are [[convection cell]]s in the [[Sun]]'s [[photosphere]]. They are caused by [[convection current|currents]] of [[Plasma (physics)|plasma]] in the Sun's [[convective zone]], directly below the photosphere. The grainy appearance of the photosphere is produced by the tops of these convective cells; this patternisreferred to as '''granulation'''. |
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The rising part of |
The rising part of each granule is located in the center, where the plasma is hotter. The outer edges of the granules are darker due to cooler descending plasma. (The terms ''darker'' and ''cooler'' are strictly by comparison to the brighter, hotter plasma. According to the [[Stefan–Boltzmann law]], [[luminosity]] increases with the fourth power of temperature, causing even a small loss of heat to produce a large luminosity contrast.) In addition to the visible appearance, which can be explained by [[convection|convective motion]], [[Doppler shift]] measurements of the light from individual granules provides evidence for the [[convective]] nature of the granules. |
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A typical granule has a diameter on the order of {{convert|1500|km}}<ref name="JBZ">{{cite book |title=Sunquakes: Probing the Interior of the Sun |publisher=Johns Hopkins University Press |first=Jack B. |last=Zirker |page=2 |date=2003 |isbn=0-8018-7419-X |oclc=919928822}}</ref> and lasts 8 to 20 minutes before dissipating.<ref>{{cite journal |title=Lifetime of Solar Granules |journal=[[The Astrophysical Journal]] |first1=J. |last1=Bahng |first2=M. |last2=Schwarzschild |name-list-style=amp |volume=134 |page=312 |date=September 1961 |doi=10.1086/147160 |bibcode=1961ApJ...134..312B|doi-access=free }}</ref> At any one time, the [[Sun]]'s surface is covered by about 4 million granules. Below the photosphere is a layer of "[[Supergranulation|supergranules]]" up to {{convert|30000|km}} in diameter with lifespans of up to 24 hours. |
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A typical granule has a diameter on the order of 1,500 kilometers<ref name="JBZ">{{cite book |
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| first = J. B. |
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| title = Sunquakes |
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| publisher = Johns Hopkins University Press |
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| year = 2003 |
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| pages = 2 |
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| jfm = }}</ref> and lasts 8 to 20 minutes before dissipating. At any one time, the [[Sun]]'s surface is covered by about 4 million granules. Below the photosphere is a layer of "[[Supergranulation|supergranules]]" up to 30,000 kilometers in diameter with lifespans of up to 24 hours. |
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[[File:Sun poster.svg|thumb|left|320px|Granules in the context of the Sun's structure |
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{| style="width:100%;" |
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{{·}}'''Granules'''<br> |
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{{·}}[[Sunspot]]<br> |
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{{·}}[[Photosphere]]<br> |
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{{·}}[[Chromosphere]] |
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| valign=top | |
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{{·}}[[Convection zone]]<br> |
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{{·}}[[Radiation zone]]<br> |
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{{·}}[[Tachocline]]<br> |
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{{·}}[[Solar core]] |
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| valign=top | |
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{{·}}[[Corona]]<br> |
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{{·}}[[Solar flare|Flare]]<br> |
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{{·}}[[Solar prominence|Prominence]]<br> |
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{{·}}[[Solar wind]] |
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]] |
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{{clear|left}} |
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== References == |
== References == |
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{{Reflist}} |
{{Reflist}} |
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==External links== |
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*{{Commons category inline}} |
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{{The Sun}} |
{{The Sun}} |
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{{DEFAULTSORT:Granule (Solar Physics)}} |
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[[Category:Sun]] |
[[Category:Sun]] |
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[[Category:Solar phenomena]] |
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{{sun-stub}} |
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Insolar physics and observation, granules are convection cells in the Sun's photosphere. They are caused by currentsofplasma in the Sun's convective zone, directly below the photosphere. The grainy appearance of the photosphere is produced by the tops of these convective cells; this pattern is referred to as granulation.
The rising part of each granule is located in the center, where the plasma is hotter. The outer edges of the granules are darker due to cooler descending plasma. (The terms darker and cooler are strictly by comparison to the brighter, hotter plasma. According to the Stefan–Boltzmann law, luminosity increases with the fourth power of temperature, causing even a small loss of heat to produce a large luminosity contrast.) In addition to the visible appearance, which can be explained by convective motion, Doppler shift measurements of the light from individual granules provides evidence for the convective nature of the granules.
A typical granule has a diameter on the order of 1,500 kilometres (930 mi)[1] and lasts 8 to 20 minutes before dissipating.[2] At any one time, the Sun's surface is covered by about 4 million granules. Below the photosphere is a layer of "supergranules" up to 30,000 kilometres (19,000 mi) in diameter with lifespans of up to 24 hours.
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