  Supernova can be polarized by an asymmetry in the explosion process, an
off-center source of illumination, scattering in an envelope distorted by
rotation or a binary companion, or scattering by the circumstellar dust.
Careful polarimetry is the most powerful tool to study the 3-D geometry of
supernovae. A deep understanding of the 3-D geometry of SNe is essential in
using them for calibrated distance indicators.
