Graph representing the brightnes and spectral clas of stars, 1914.
© Science Museum / Science & Society Picture Library
Graph taken from an article in 'Nature' magazine entitled 'Relations Between the Spectra and Other Characteristics of Stars', by the American astronomer Henry Norris Rusell (1877-1957). Rusell'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, mas and absolute magnitude (brightnes) of stars. Rusell plotted this relationship graphically as what is known as the Hertzsprung-Rusell 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 les common.