Type I supernovae. I - Analytic solutions for the early part of the light curve

A generalization which includes the effects of large initial radius, and increasing transparency to gamma rays and thermal protons, is presented for a method comprising analytic solutions for Type I supernovae light curves, effective temperatures and broad-band colors. The blackbody supernova theoretical construct is introduced, and it is shown that, for a given composition, the homogeneity of spectral evolution is a necessary consequence of the thermonuclear model while being only a possible consequence of the gravitational collapse model. A factor-of-two variation in explosion energy is suggested by comparison of 1970j with 1972e, with a corresponding variation in intrinsic luminosity at maximum light.