The Luminosity Calibration of SNe Ia: Present Status

Blue Supernovae of Type Ia (SNe Ia) have become the most important objects in cosmology being of exceptionally uniform luminosity. Used as relative distance indicators they map deviations from pure Hubble flow and determine the cosmological constant Lambda. Once their absolute magnitude is determined they provide the best estimate of the large-scale value of the Hubble constant H_0. An HST project is reviewed where Cepheid distances are used for the luminosity calibration of SNe Ia. The mean luminosity of 8 SNe Ia is M_B(max)= -19.47 +/- 0.07, M_V(max)= -19.48 +/- 0.07, corresponding – after small corrections for second parameters – to H_0(cosmic)= 59 +/- 5.