Now that we have information about opacity, we are almost ready to undertake the calculation of a model of the first segment of the Sun which is accessible to modeling: the photosphere. In calculating this model, we do not inquire into the origin of the energy which flows through the solar atmosphere. Instead, we simply take the luminosity (or flux) as a given, and calculate how the physical parameters of the medium arrange themselves so as to “handle” the energy which is passing through.