  Light echoes, light from a variable source scattered off dust, have been
observed for over a century. The recent discovery of light echoes around
centuries-old supernovae in the Milky Way and the Large Magellanic Cloud have
allowed the spectroscopic characterization of these events, even without
contemporaneous photometry and spectroscopy using modern instrumentation. Here
we review the recent scientific advances using light echoes of ancient and
historic transients, and focus on our latest work on SN 1987A's and Eta
Carinae's light echoes.
