A system of convective cells, called supergranules, with diameters of about 30,000 km (20,000 mi) and lifetimes of 1 or 2 days, which cover the visible disc of the Sun, the photosphere. Smaller convection cells called granules, which are about 1500 km (900 mi) across and have lifetimes of about 10 min, are seen through a telescope in white-light images of the photosphere, but the supergranules are not visible this way.

The supergranulation is seen in Dopplergrams that measure motions in the photosphere. The gas flows horizontally from the centre to the edge of each supergranule, carrying along the photospheric magnetic field that is detected by the Zeeman effect in magnetograms. The magnetism is concentrated at the edges of the supergranules, forming polygon-shaped structures called the magnetic network, which is also detected as bright calcium emission in the overlying chromosphere.