Supernovae and the Hubble Constant (or Butthead's Revenge)

Physical models of Type Ia supernovae (SN Ia) that do not depend on secondary calibrators have indicated that the Hubble Constant must be about 65 km/s/Mpc for well over a decade with the range of uncertainty shrinking with the sophistication of the models. This estimate is in good agreement with those based on HST observations of Cepheid variables and with purely empirical methods based on SN Ia calibrated with Cepheids. The prospects of progress in understanding the physics of the explosion of SN Ia and of their application to measure other cosmological parameters is reviewed. Despite the rather complex nature of their atmospheres, SN Ia may give a more reliable estimate of distances than Type II. The latter depend on remaining uncertainties in the scattering atmospheres, the helium abundance and possible systematic effects due to distortions of the envelope that will not average out even in a large sample