<P> The Hertzsprung--Russell diagram, abbreviated H--R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their stellar classifications or effective temperatures . More simply, it plots each star on a graph measuring the star's brightness against its temperature (color). It does not map any locations of stars . The related colour--magnitude diagram (CMD) plots the apparent magnitudes of stars against their colour, usually for a cluster so that the stars are all at the same distance . </P> <P> The diagram was created circa 1910 by Ejnar Hertzsprung and Henry Norris Russell and represents a major step towards an understanding of stellar evolution . </P> <P> In the nineteenth - century large - scale photographic spectroscopic surveys of stars were performed at Harvard College Observatory, producing spectral classifications for tens of thousands of stars, culminating ultimately in the Henry Draper Catalogue . In one segment of this work Antonia Maury included divisions of the stars by the width of their spectral lines . Hertzsprung noted that stars described with narrow lines tended to have smaller proper motions than the others of the same spectral classification . He took this as an indication of greater luminosity for the narrow - line stars, and computed secular parallaxes for several groups of these, allowing him to estimate their absolute magnitude . </P>

What kind of star is the sun in hertzsprung russell diagram