By this time Prout’s hypothesis that all the elements are compounds of hydrogen had been revived by physicists in a somewhat more elaborate form.

She found that hydrogen and helium are the most abundant elements in stars, though this conclusion was not generally accepted until it was confirmed four years later by the noted American astronomer Henry Norris Russell. In 1925 Cecilia Payne, a graduate student from Britain at Harvard College Observatory, analyzed the spectra of stars using statistical atomic theories that related them to temperature, density, and composition. Astrophysicists were perplexed: what source of energy has kept the Sun shining for such a long time? Evidence from radiometric dating, starting with the work of the British physicist Ernest Rutherford in 1905, showed that Earth is several billion years old. The gravitational energy released by this condensation could be transformed into heat, but calculations by Hermann von Helmholtz and Lord Kelvin indicated that this process would provide energy to keep the Sun shining for only about 20 million years. The idea that stars are formed by the condensation of gaseous clouds was part of the 19th-century nebular hypothesis ( see above). These theories also offered a fundamental basis for chemistry by showing how the elements could have been synthesized in stars. Just as the development of cosmology relied heavily on ideas from physics, especially Einstein’s general theory of relativity, so did theories of stellar structure and evolution depend on discoveries in atomic physics.

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