Figure 9-22The Solar Model (a) Thermonuclear reactions occur in the Sun’s core, which extends to a distance of 0.25 solar radius from the center. In this model, energy from the core radiates outward to a distance of 0.7 solar radius. Convection is responsible for energy transport in the Sun’s outer layers. (b) The Sun’s internal structure is displayed here with graphs that show how the luminosity, mass, temperature, and density vary with the distance from the Sun’s center. The solar radius (the distance from the Sun’s center to the photosphere) equals 696,000 km (432,000 mi). (c) The nine most common elements in the Sun, by the numbers of atoms of each and by the percentage of the Sun’s total mass they each comprise.