The energy of most stars results from the fusion of hydrogen nuclei to helium nuclei. The temperature of the interior of the sun (a typical star) is 15 x 106 K. At this temperature, virtually no nuclei have enough kinetic energy to overcome the electrostatic repulsion between nuclei and approach each other closely enough to undergo fusion. Therefore, when Eddington proposed in 1920 that nuclear fusion is the source of stellar energy, his idea was rejected. Explain why fusion does occur in stars, despite the above-mentioned apparent difficulty.