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{{Structure of the Sun|right}} |
{{Structure of the Sun|right}} |
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'''Granules''' on the [[photosphere]] of the [[Sun]] are caused by [[convection current]]s ([[thermal column]]s, [[Bénard cells]]) of [[Plasma (physics)|plasma]] within the Sun's convective zone. |
'''Granules''' on the [[photosphere]] of the [[Sun]] are caused by [[convection current]]s ([[thermal column]]s, [[Bénard cells]]) of [[Plasma (physics)|plasma]] within the Sun's convective zone. The grainy appearance of the solar photosphere is produced by the tops of these convective cells and is called ''granulation''. |
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The rising part of the granules is located in the center where the [[plasma (physics)|plasma]] is hotter. The outer edge of the granules is darker due to the cooler descending plasma. (The terms ''darker'' and ''cooler'' are strictly by comparison to the brighter, hotter plasma. Since [[Stefan–Boltzmann law|luminosity increases with the fourth power of temperature]], even a small loss of heat produces a large luminosity contrast; this "cooler", "darker" plasma is still far hotter and vastly brighter than a thermite reaction.) In addition to the visible appearance, which would be explained by [[convection|convective motion]], [[Doppler shift]] measurements of the light from individual granules provides evidence for the [[convective]] nature of the granules. |
The rising part of the granules is located in the center where the [[plasma (physics)|plasma]] is hotter. The outer edge of the granules is darker due to the cooler descending plasma. (The terms ''darker'' and ''cooler'' are strictly by comparison to the brighter, hotter plasma. Since [[Stefan–Boltzmann law|luminosity increases with the fourth power of temperature]], even a small loss of heat produces a large luminosity contrast; this "cooler", "darker" plasma is still far hotter and vastly brighter than a thermite reaction.) In addition to the visible appearance, which would 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 |last-author-amp=y |volume=134 |page=312 |date=September 1961 |doi=10.1086/147160 |bibcode=1961ApJ...134..312B}}</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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Very hot plasma with temperature as high as 5800 degree Celsius. |
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A typical granule has a diameter on the order of {{convert| |
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== Gallery == |
== Gallery == |
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Granules on the photosphere of the Sun are caused by convection currents (thermal columns, Bénard cells) of plasma within the Sun's convective zone. The grainy appearance of the solar photosphere is produced by the tops of these convective cells and is called granulation.
The rising part of the granules is located in the center where the plasma is hotter. The outer edge of the granules is darker due to the cooler descending plasma. (The terms darker and cooler are strictly by comparison to the brighter, hotter plasma. Since luminosity increases with the fourth power of temperature, even a small loss of heat produces a large luminosity contrast; this "cooler", "darker" plasma is still far hotter and vastly brighter than a thermite reaction.) In addition to the visible appearance, which would 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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