who worked in America. She developed a temperature scale for the various spectral types of stars based on the strengths of their spectral lines. In 1925, in a study of the relative abundances of elements in stars of various ages, she established that hydrogen is the major constituent of stars. With the Russian-American astronomer Sergei Illarionovich Gaposchkin (1898–1984), whom she married in 1934, she began a huge programme of measuring the magnitudes of variable stars from photographic plates, which resulted in a catalogue of variables published in 1938. A similar joint study of variables in the Magellanic Clouds appeared in 1971.