Granule (solar physics)

Short description: Convection cell in the Sun's photosphere

High-resolution image of the Sun's surface taken by the Daniel K. Inouye Solar Telescope (DKIST). An illustration of the structure of the Sun

* Granules
* Sunspot
* Photosphere
* Chromosphere
* Convection zone
* Radiation zone
* Tachocline
* Solar core
* Solar corona
* Flare
* Prominence
* Solar wind

A granule is a convection cell in the Sun's photosphere. They are caused by convection currents of plasma in the Sun's convective zone, directly below the photosphere. 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. According to the Stefan–Boltzmann law, luminosity increases with the fourth power of temperature leading to even a small loss of heat producing a large luminosity contrast.) 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.

## Gallery

* Granulation motions on the Sun's surface observed by the Swedish Solar Telescope.

Granulation motions on the Sun's surface observed by the Swedish Solar Telescope.

* Detailed view of a sunspot and surrounding solar surface. The dense pattern of cells (unrelated to the sunspot) is granulation; the individual cells are granules.

## References

1. ↑ Zirker, Jack B. (2003). Sunquakes: Probing the Interior of the Sun. Johns Hopkins University Press. p. 2. ISBN 0-8018-7419-X. OCLC 919928822.
2. ↑ Bahng, J.; Schwarzschild, M. (September 1961). "Lifetime of Solar Granules". The Astrophysical Journal 134: 312. doi:10.1086/147160. Bibcode: 1961ApJ...134..312B.

## External links

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The Sun

Internal structure|

* Core
* Radiation zone
* Tachocline
* Convection zone

Atmosphere|

| Photosphere|

* Supergranulation
* Granule
* Faculae
* Sunspot

|

Chromosphere|

* Plage
* Spicule
* Moreton wave

Corona|

* Transition region
* Coronal hole
* Coronal loop
* Coronal mass ejection
* Prominence
* Helmet streamer
* Supra-arcade downflows

Variation|

* Solar cycle
* List of solar cycles
* Solar maximum
* Solar minimum
* Wolf number
* Solar wind
* Flare
* Helioseismology

Heliosphere|

* Current sheet
* Termination shock
* Heliosheath
* Heliopause
* Bow shock

Related|

* Heliophysics
* Solar activity
* Solar astronomy
* Solar dynamo
* Eclipse
* Solar energy
* Solar neutrino
* Solar observation
* Solar phenomena
* Solar physics
* Solar System
* Solar telescope
* Solar time
* Space climate
* Space weather
* Standard solar model
* Star
* Sunlight radiation

* Spectral class: G-type main-sequence star

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