So far, when we have discussed the Sun, we have been interested in the material which extends from the visible surface downward into the interior of the Sun. The visible surface, the “photosphere” (the “light sphere”), provides the light which dominates human vision. Our model of the interior of the Sun, extending over the entire radial extent from center to photosphere, spanned a radial distance of some 700,000 km. When we computed the model, we did so in three segments, focusing on distinct laws of physics which play dominant roles in each segment. As it turned out, the three segments were found to be of unequal radial depth. The model of the deep interior (Chapter 9) extended over some 500,000 km. The model of the convection zone (Chapter 7) had a depth of some 200,000 km. And the model of the photosphere (Chapter 5) spanned no more than a few hundred kilometers in linear extent.