Light Echoes of Transients and Variables in the Local Universe
  Astronomical light echoes, the time-dependent light scattered by dust in the
vicinity of varying objects, have been recognized for over a century.
Initially, their utility was thought to be confined to mapping out the
three-dimensional distribution of interstellar dust. Recently, the discovery of
spectroscopically-useful light echoes around centuries-old supernovae in the
Milky Way and the Large Magellanic Cloud has opened up new scientific
opportunities to exploit light echoes.
  In this review, we describe the history of light echoes in the local Universe
and cover the many new developments in both the observation of light echoes and
the interpretation of the light scattered from them. Among other benefits, we
highlight our new ability to spectroscopically classify outbursting objects, to
view them from multiple perspectives, to obtain a spectroscopic time series of
the outburst, and to establish accurate distances to the source event. We also
describe the broader range of variable objects whose properties may be better
understood from light echo observations. Finally, we discuss the prospects of
new light echo techniques not yet realized in practice.
