Definition of: Hertzsprung-Russell diagram

(hert′sprung′·rus′əl) Astron.
A classification of stars plotted on a chart in which the luminosity increases on a vertical scale from bottom to top and the color or spectral type changes from blue or white to red on a horizontal scale from left to right: also called Russell diagram. See MAIN SEQUENCE. [after Ejnar Hertzsprung, born 1873, Dutch astronomer, and Henry Norris Russell, 1877–1957, U.S. astronomer]