What can the occult do for you?
  Interstellar dust is still a dominant uncertainty in Astronomy, limiting
precision in e.g., cosmological distance estimates and models of how light is
re-processed within a galaxy. When a foreground galaxy serendipitously overlaps
a more distant one, the latter backlights the dusty structures in the nearer
foreground galaxy. Such an overlapping or occulting galaxy pair can be used to
measure the distribution of dust in the closest galaxy with great accuracy. The
STARSMOG program uses Hubble to map the distribution of dust in foreground
galaxies in fine (<100 pc) detail. Integral Field Unit (IFU) observations will
map the effective extinction curve, disentangling the role of fine-scale
geometry and grain composition on the path of light through a galaxy. The
overlapping galaxy technique promises to deliver a clear understanding of the
dust in galaxies: geometry, a probability function of dimming as a function of
galaxy mass and radius, and its dependence on wavelength.
