Graph representing the brightness and spectral class of stars, 1914

Graph representing the brightness and spectral class of stars, 1914. Graph taken from an article in 'Nature' magazine entitled 'Relations Between the Spectra and Other Characteristics of Stars', by the American astronomer Henry Norris Russell (1877-1957). Russell's main contribution to astronomy was his work concerning stars. Working with A R Hinks at Cambridge on parallaxes (the distance of a star from Earth), he discovered a correlation existed between the spectral type, mass and absolute magnitude (brightness) of stars. Russell plotted this relationship graphically as what is known as the Hertzsprung-Russell diagram. He found that the large majority of stars he observed fell within a narrow diagonal band on the graph, the 'main sequence', and that supergiant and dwarf stars were considerably less common. ©SSPL/Science Museum