By 1910 he had accumulated data on enough stars for him to plot a diagram of their absolute magnitude against their spectral type, finding that red stars fell into two groups, giants and dwarfs, but he was unaware that E. Hertzsprung had done the same in 1906. This diagram, further developed by Russell in 1913, is now known as the Hertzsprung–Russell diagram. Russell also evolved a method of calculating the masses of binary stars. In 1928 he established the composition of the Sun’s atmosphere from its spectrum, and went on to suggest that all stars contain a high proportion of hydrogen, a conclusion originally reached by C. H. Payne-Gaposchkin.