. I . Optical and Ultraviolet

Scattering and absorption properties at optical and ultraviolet wavelengths are calculated for an interstellar dust model consisting of carbonaceous grains and amorphous silicate grains. Polarization as a function of scattering angle is calculated for selected wavelengths from the infrared to the vacuum ultraviolet. The widely-used Henyey-Greenstein phase function provides a good approximation for the scattering phase function at wavelengths between ∼0.4 and 1µm, but fails to fit the calculated phase functions at shorter and longer wavelengths. A new analytic phase function is presented. It is exact at long wavelengths, and provides a good fit to the numerically-calculated phase function for λ > 0.27µm. Observational determinations of the scattering albedo and cos θ show considerable disagreement, especially in the ultraviolet. Possible reasons for this are discussed.