Solar structure. Cutaway computer artwork showing the structure of the Sun. At the Sun's core (centre) hydrogen atoms undergo nuclear fusion, producing helium atoms and releasing heat and light energy as photons. These radiate outwards through the inner region (radiative zone, yellow) to the outer convection zone layer (orange). Here, solar plasma rises in thermal columns to the visible surface (photosphere) and falls back to the interior in convection currents (squared lines). Intense magnetic fields on the surface of the Sun inhibit convection in some areas, causing these areas to have lower temperatures than others and causing the appearance of dark spots known as sunspots (lower right).