English: The illustration shows a Hertzsprung-Russell diagram, where the effective temperature of stars, Teff, is plotted on the primary axis (logarithmic, increasing to the left) and their luminosity, L, in units of the Sun is plotted up the secondary axis (logarithmic). The absolute bolometric magnitude associated with the luminosity, Mbol, can be seen on the axis to the right. The choice of axes allows one to draw straight lines with constant stellar radius. The radius varies greatly from the lower left corner to the upper right one, and it is given in units of the Sun's radius. The zero-age main sequence (“ZAMS”) is marked with a thick black curve. The positions of some well-known or extreme stars are indicated with an orange disc and the star’s name.