The Hertzsprung-Russell diagram (commonly abbreviated as the H-R diagram) is a scatter plot of stars indicating the relationship between the absolute magnitudes or luminosities of the stars compared to their spectral ratings or effective temperatures. More simply, each star is plotted on the graph to measure its brightness compared to its temperature (color).
Hertzsprung-Russell diagram.
The diagram was created around 1910 by Ejnar Hertzsprung and Henry Norris Russell and represents an important step toward understanding stellar evolution or "the way stars go through sequences of radical and dynamic change over time."
It was made in 1905 by the astronomer Ejnar Hertzsprung and, independently, in 1913 by Henry Norris Russell. The Hertzsprung diagram showed the luminosity of stars as a function of their color, while the initial Russell diagram showed the luminosity as a function of spectral type. Both diagrams are equivalent.