As a result of the calculations in Chapters 5, 7, and 9, we have obtained a model for the interior of the Sun. Is there any way to check our model, to see if it is correct?

In the 1960s, only one answer existed for this question: we need to detect a certain kind of energetic particle (neutrinos) which emerges from nuclear reactions in the core of the Sun. The goal of such experiments would be to check that the numbers of neutrinos which reach the Earth, as well as their energies, are consistent with the properties we calculated for nuclear reactions in the solar core.