UV Opacity in Nearby Galaxies and Application to Distant Galaxies

The effects of dust opacity on the radiation of nearby and distant galaxies are reviewed. The geometrical distribution of the dust inside the galaxy plays a fundamental role in determining the wavelength dependence of the obscuration and the opacity of the galaxy. In the local Universe, late Hubble type galaxies appear to contain enough dust that corrections for the effect of obscuration become important. This is true expecially at blue and UV wavelengths, i.e. in the wavelength range of interest for studies of massive stars and star formation processes. Multiwavelength observations provide a powerful tool for characterizing the reddening caused by dust. A `recipe' is given for removing the dust reddening and recovering the UV and optical light in star-forming galaxies