Remote Observations of Interstellar Dust
Information about the nature of interstellar dust is contained implicitly in data of various phenomena in which dust influences electromagnetic radiation. The phenomena are observed over wavelengths from radio to X-ray in instruments on Earth and aboard orbiting spacecraft. Among the various phenomena are the extinction and polarization of starlight, and the presence of specific solid state absorption features in the spectrum. Emissions from dust in bands and in continua are also detected, sometimes from rather special interstellar locations. The information contained in these observations can be used to constrain possible models of the physical and chemical nature of dust. In addition, since atoms that are in dust cannot be present in the gas phase and are said to be depleted from the standard interstellar abundances, measured depletions also constrain the chemical nature of possible models of interstellar dust.