Ejnar Hertzspung sketched his first luminosoty-color diagram of star clusters in 1908. German astronomer Hans Rosenberg, who likely knew of Hertzsprung's work, published such a diagram in 1910, and Hertzsprung himself published several in 1911. At the time, he was an unknown. In contrast, Henry Norris Russell was one of America's foremost astronomers. In 1913, unaware of Hertzsprung's work, he plotted his own diagram. Because of Russell's prestige, astronomers first called the plot the Russell diagram, then the Russell-Hertzsprung diagram and finally—getting the historical order right—the Hertzsprung-Russell diagram.What a plot!
The H-R diagrams is a plot of the visual luminosity versus the surface temperature of stars including supergiants, white and brown dwarfs and, of course, our sun [2.1, 3]. The main groups of clustered or roughly lined-up stars in the diagram represent supergiants, giants, main sequence stars and white dwarfs. The H-R diagram is a vital pattern recognition tool to explore similarities and differences between stars and to compare some of their properties. With the help of the H-R diagram, for example, you can check your understanding of the life cycle of a star .
 Autorenkollektiv: Lexikon der Naturwissenschaftler. Spektrum Akademischer Verlag, Heidelberg•Berlin, 2000.
 Ken Croswell: The Periodic Table of the Cosmos. Sci. Am. July 2011, 305 (1), 44-49. DOI: dx.doi.org/10.1038/scientificamerican0711-44.
[2.1] A User's Guide to the H-R Diagram: www.nature.com/scientificamerican/journal/v305/n1/box/scientificamerican0711-44_BX1.html.
 Hertzsprung-Russel Diagram: cassfos02.ucsd.edu/public/tutorial/HR.html.
 Hertzsprung-Russel Diagram: aspire.cosmic-ray.org/labs/star_life/hr_diagram.html.