Ultraviolet observations of interstellar dust

A large fraction of astronomical observations in the UV are affected by extinction due to interstellar dust in the line of sight. The shape of the extinction curve varies markedly around the sky, especially in regions of nebulosity such as the Orion Nebula. The variations of the shape provide clues to the nature of the dust. Additional insight into the physical properties of dust can be obtained from reflected UV starlight as observed in NGC7023 by IUE and in the faint arms of M101 as photographed by a sounding rocket