Q:   Suppose the central region of the Sun has density rho, temperature
           T = 15 million K, and chemical composition X = 0.88 and
           X(CNO) = 0.02.   Which process generates more
           power -- the proton-proton chain, or the CNO cycle?  How much more?


           We can insert the values for temperature and chemical composition
           into the formula for epsilon(pp) to find the energy generated
           by the proton-proton chain; it will still have a factor of the
           density, rho, but that's okay.


                  epsilon(pp)  =  3.92 x 10^(4) * rho    (J/s)/kg/(kg/m^3)


           We can repeat this procedure to compute the rate of energy
           generation via CNO cycle, which gives


                  epsilon(CNO) =  3.57 x 10^(3) * rho    (J/s)/kg/(kg/m^3)


           Clearly, in this region, the p-p chain produces more energy
           than the CNO cycle, by about one order of magnitude.