9.8	Interstellar Extinction

Interstellar extinction can dramatically reduce the count rate detected from your source, particularly if you are working in the ultraviolet range but are inferring source brightnesses from optical data. Conversely, optically obscured objects may be much brighter in the IR than in the optical.

The Exposure Time Calculator includes the ability to correct exposure-time estimates for interstellar extinction based on the color excess E(B−V). It may also be useful to refer to the standard references on interstellar extinction and its variations with location and metallicity, e.g., Fitzpatrick (1999, PASP, 111, 63) and references therein.