The H-R (Hertzburg-Russell) diagram is a diagram used in stellar astronomy to plot the property of stars. There are two equivalent forms. One is the observer's form which plots the color of the star on one axis and the absolute magnitude on the other axis. The theoreticians form plots the temperature of the star in one access and the luminosity of the star on the other.
The H-R diagram is used to defined different types of stars. Also it is used to match theoretical predictions of stellar evolution using computer models with observations of actual stars.