False-colour image of the Sun, showing sunspots (green dots), active regions (large red areas) and filaments (green lines). Sunspots are pockets of cool, dark gas which occur in magnetically active regions, often in groups. A filament is a jet of hot gas reaching up into the Sun's corona. A filament occurring near the Sun's limb (edge) would appear bright and would be called a prominence. The grainy appearance (granulation) of the Sun's surface (photosphere) is caused by pockets of hot gas rising and falling. We see the tops of these pockets, or convection cells, as they rise to the surface. The photograph was taken in the red light emitted by hydrogen atoms.