star types



  • Stars are classified according to spectral types in order of their surface temperature. From hottest to coolest the types are O, B, A, F, G, K and M. Within each type are subtypes 0 (hottest) to 9 (coolest), so that B9 is slightly hotter than A0. Most stars occupy positions on the main sequence of the Hertzsprung-Russell diagram, where the relation between star type and magnitude and mass is simple, but there are also groups like the giants, supergiants and white dwarfs which do not obey this relationship.