Hertzsprung-Russell diagram, in astronomy, graph in which the absolute magnitudes (intrinsic brightness) of stars are plotted against their spectral types (temperatures).
This Hertzsprung-Russell diagram shows a group of stars in various stages of their evolution. By far the most prominent feature is the main sequence, which runs from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) of the diagram.
The Hertzsprung–Russell diagram, or H–R diagram, is a plot of stellar luminosity against surface temperature. Most stars lie on the main sequence, which extends diagonally across the H–R diagram from high temperature and high luminosity to low temperature and low luminosity.
The classical HR diagram, first constructed in 1914 by Henry Norris Russell (to which was added the work of Ejnar Hertzsprung), is a plot of absolute visual magnitude against spectral class. The natures of nearly all the myriad kinds of stars are beautifully expressed within its confines.