Type Ia Supernovae as Standard Candles

Observations are compiled to construct a mean light curve of SNe I in different colors. Individual SNeI show generally no systematic deviations from these templet light curves, and occasional deviations are explained as photometric errors, which can be quite severe in the case of SNe. The peak luminosity of absorption-free SNe I is also uniform with an intrinsic rms scatter of <0. 3 mag. The calibration of the peak luminosity yields MB(max) = -20. 0 ± 0. 4, which requires Ho = 43 t 10 km s−1 Mpc−1. SNeI are probably among the best standard candles known and hence have in view of their high luminosity important applications for distance determinations and for cosmological tests to be performed with Space Telescope.