It is a thin layer of low density gas belt that emits a large amount of visible photons or light. The surface of the photosphere is marked by granulation, a pattern produced by gas currents rising from below the photosphere layer. The layer above the photosphere is called the chromosphere. It is a thin hot layer of gas just above the photosphere, and its brilliant pink color is caused by the emission lines in its spectrum. Filtergrams of chromosphere show large jets called spicules extending up into the corona.
Corona is the outermost layer of sun's atmosphere.
It is composed of very low density and very hot gas extending at least 30 solar radii. It has a high temperature of 2 million degrees Kelvin that is maintained by the magnetic field and the rotation of the sun. The solar wind starts out from the outer part of the corona. From time to time, the earth together with other planets in the solar system, is bathed with the solar wind. Solar astronomers study the motion, density and the temperature of the gases below the solar surface.