Quite early in history people understood that if the sun did not shine, everything would remain dark and cold and life would come to an end.
What is the sun made of and how can it keep shining on and on and never stop?
Asimov takes us through the discoveries of Galileo, Copernicus, Cassini, Newton, Helmholtz, and other scientists, to the discovery of nuclear energy, which later led to the discovery of hydrogen fusion. Hydrogen fusion produces more energy than any other nuclear reaction. It supplies energy year after year for billions of years.
This is a book about nuclear energy after a fashion, although not as explicitly so as How Did We Find Out About Nuclear Power?, and is aimed at a slightly older audience than What Makes the Sun Shine?. This is a good place for the target audience to go to get information on this subject, but adults would better reread Asimov’s New Guide to Science to get the same information more thoroughly presented.