Illustration of the structure of the sun. At the sun's core (pale yellow) 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 (reddish orange). Here, solar plasma rises in thermal columns to the visible surface (photosphere orange at left). Intense magnetic fields on the surface of the sun inhibit convection, causing some areas to have lower temperatures than others (sunspots, dark spots). These also cause solar prominences (loops), where charged gas is drawn across areas of opposite polarity. Flares take place in active regions and provoke a sudden increase of the radiative flux emitted from the corona. The corona is an aura of plasma that surrounds the sun.