Following the spirit of Chapters 5 and 7, we now proceed deeper into the Sun and calculate a radial profile for the physical variables. As in the earlier chapters, we still refrain from considering the origin of the energy which is passing through. Our aim is purely mechanical: given a total luminosity, how does the medium arrange itself so as to “handle” the energy which is passing through? A complete model of the Sun would of course include a description of the processes whereby the energy is generated: we will discuss that in Chapter 11. But in this chapter, we do not attempt to calculate a complete model. Our goal is as follows: given the solar luminosity as a boundary condition, what can we deduce about the structure of the Sun?