This system of classifying stars is based on luminosity, spectral type, absolute magnitude (star’s radius), and finally surface temperature in kelvin or celsius. The diagram is named after Danish and American astronomers Ejnar Hertzsprung and Henry Russell. The Hertzsprung-Russell (H—R) diagram gives us a view of our sun’s position in it, a standard of one in a main sequence. Once the temperatures of stars were plotted against their luminosities, it has been observed that stars tend to be in groups.