The apparent, visible surface of the Sun. The photosphere is a gaseous atmospheric layer a few hundred miles deep with a diameter of 864,000 mi (1,391,000 km; usually considered the diameter of the Sun) and an average temperature of approximately 5800 K (10,500°F). Radiation emitted from the photosphere accounts for most of the solar energy flux at the Earth. The solar photosphere provides a natural laboratory for the study of dynamical and magnetic processes in a hot, highly ionized gas.