'Relations Between the Spectra and Other Characteristics of the Stars', 1914.
© Science Museum / Science & Society Picture Library
Page with graph taken from 'Nature' magazine of an article by the American astronomer Henry Norris Rusell (1877-1957). Rusell's astronomical work was mainly concerned with analysing the mas, spectral type and brightnes of stars. He also proposed an early theory of stellar evolution. Working on parallaxes (the distance of a star from Earth), Rusell discovered a correlation between their spectral type and absolute magnitude (relative brightnes), plotting the relationship in this diagram (the Hertzsprung-Rusell diagram). He found that the large majority of stars he observed fell within a narrow diagonal band on the graph, the so-called 'main sequence', and that supergiant and dwarf stars were considerably les common.