This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Granule" solar physics  – news  · newspapers  · books  · scholar  · JSTOR (March 2014) ()

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.

© About the Author, CC BY 4.0

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

© Kelvinsong, CC BY-SA 3.0

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

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.

• Play media

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

• 

  © Luc.rouppe, CC BY-SA 4.0

  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.

• Media related to Granules (solar physics) at Wikimedia Commons