  We investigate the influence of scattering and geometry on the attenuation
curve in disc galaxies. We investigate both qualitatively and quantitatively
which errors are made by either neglecting or approximating scattering, and
which uncertainties are introduced due to a simplification of the star-dust
geometry. We find that the magnitude of these errors depends on the inclination
of the galaxy, and in particular that for face-on galaxies, the errors due to
an improper treatment of scattering dominate those due to an imprecise
star-dust geometry. Therefore we argue that in all methods which aim at
determining the opacity of disc galaxies, scattering should be taken into
account in a proper way.

Astrophysics