structural:reformatting, quality:corruption
Surface gravity

The supergiant luminosity class is assigned on the basis of spectral features that are largely a measure of surface gravity, although such stars are also affected by other properties such as microturbulence. Supergiants typically have surface gravities of around log(g) 2.0 cgs and lower, although bright giants (luminosity class II) have statistically very similar surface gravities to normal Ib supergiants. Cool luminous supergiants have lower surface gravities, with the most luminous (and unstable) stars having log(g) around zero. Hotter supergiants, even the most luminous, have surface gravities around one, due to their higher masses and smaller radii.