Prof. William Keel
I will describe a program to trace the present-day properties of dust in galaxies, particularly as these properties affect the radiation passing through disk galaxies. Use of rare cases of silhouetted galaxies circumvents many uncertainites in modelling the internal radiative transfer, and has been reinvigorated through a large new sample selected in the public-computing GalaxyZoo program. This sample is large enough, in combination with the GALEX UV survey, to give us a direct comparison of UV extinction in galaxies with similar measurements on Hubble data at high redshift, helping resolve substantial uncertainties allowed by models of the history of dust and gas in galaxies. Similar techniques can be used for dust deep inside some galaxies, giving hints as to the variation in the range of grain sizes with galaxy environment (as well as in the nearby Crab Nebula, an ongoing dust factory). Finally, combined Hubble and Chandra dataon nearby S0 galaxies give a glimpse into the interplay among grain formation, starbirst, and grain destruction through sputtering, and hint at a threshold level of star formation needed to sustain the grain population needed to sustain this star formation.