When the U.S. Fusion Energy Outreach Team declared the second week of May as Fusion Energy Week, they were recognizing the May 10 birthday of Cecilia Payne-Gaposchkin—the British-born American astronomer who applied principles of quantum physics, chemistry, and astronomy to become the first to realize—at the age of 25—that stars and the universe itself are mostly composed of hydrogen and helium, and that the stars could be sorted by their spectra into groups that corresponded to the temperature of the stars.