The grainy appearance of the Sun's surface, caused by large convection cells. (The Sun's energy comes to the surface as 'bubbles'.) One grain is typically 1,500 km across. 'Granules' are organised into larger, pancake shaped domains, 'supergranules', which are typically about 25,000 km across.
The cellular pattern clearly visible outside of the sunspots on this photograph is called granulation. They are associated with large scale fluid motions at and just below the photosphere; the brighter, central regions correspond to rising hotter fluid, and the darker, narrow lanes to sinking, colder fluid. Typical speeds in granular flows are of the order of a few kilometres per second.
