COSMOLOGICAL DISTANCES FROM SUPERNOVA PHOTOSPHERES

At the foundation of the quest to discover the properties of our unive rse are reliable measurements of distance. We focus on the expanding p hotosphere method as applied to type II supernovae, indicating how its independent observational tests strengthen our understanding of and c onfidence in this probe. In keeping with the spirit of this conference , we illustrate some analogies between ''freeze-out'' of abundances in cosmological or explosive nucleosynthesis and the formation of the sp ectral luminosity of the supernova. The results of the first critical test of this method, measurement of the distance to supernova 1987A in the Large Magellanic Cloud, are summarized. Plans for use of the Hubb le Space Telescope to contribute to an independent direct determinatio n of the Hubble constant are outlined, and prospects for extensions to higher redshifts are discussed.