The visible surface of a star, from which most of its energy is emitted in the form of visible and infrared radiation. The name means ‘light sphere’. The Sun’s photosphere is a thin layer about 500 km deep. Its temperature decreases steadily from about 6400 K at its base to 4400 K at the temperature minimum, where it merges with the chromosphere above. This drop in temperature with height causes limb darkening. The photosphere has a rice-grain texture called granulation, caused by rising convection cells of hot gas. Other photospheric features include sunspots, faculae, and filigree structures, all associated with strong magnetic fields. Almost all the features of the Sun’s visible-light spectrum originate in the photosphere, including the dark Fraunhofer lines.