Computer illustration showing the internal structure of the Sun. The nuclear reactions that power the Sun take place in the hot, dense central core, which extends to about a quarter of the Sun's radius. Here hydrogen fuses into helium, releasing energy. Above this is the radiative zone, where the energy is transferred between particles by energetic photons (yellow dots). This situation persists to about 70% of the Sun's radius, above which the overlying layers are cool and rarefied enough to permit convection, which occurs in the outer convective layer (orange). Here, hotter, less dense pockets of plasma rise to the surface, cool and sink (arrows), producing the granulation visible on the Sun's surface.