The quality of observational data on Type Ia supernovae has improved remarkably in the last few years, due mainly to monitoring programs with CCD-equipped detectors on small aperture telescopes at observatories across the world, and at the space observatories. I will review the recent observational characteristics of Type Ia supernovae, focusing the discussion on our observations of SN1992A in the S0 galaxy NGC 1380 in the Fornax cluster as a reference to other Type Ia events. We now have strong evidence that Type Ia events are not a homogeneous class, but vary in both color and brightness at maximum light, vary in rise time and decline from maximum, and have spectral characteristics at maximum light that are correlated with these photometric parameters. Insofar as the SBF, PNLF, and infrared Tully-Fisher distance scales are correct, the observed (uvoir) bolometric light curves also indicate that these supernovae are less luminous than expected from the models of the explosion of a C-O white dwarf at the Chandrasekhar mass.

Introduction

A stellar explosion is an unlikely physical environment to produce a homogeneous energy flux, given the fantastic brightness of a supernova at maximum light which can reach 10% of the luminosity of the whole galaxy for a period of a few weeks. Yet it is the brightness of the event that makes the use of supernovae as “standard candles” so attractive, since they can be readily observed to cosmologically interesting distances.