Artist Concept of light echo geometry  Flashes from the Past:
Echoes from Ancient Supernovae |  A team led by astronomers from
CTIO has found faint visible echoes of three ancient supernovae
by detecting their centuries-old light as it is reflected by
clouds of interstellar dust hundreds of light-years removed from
the original explosions. The oldest one is likely to have
occurred more than six hundred years ago. More in NOAO Press
Release 05-12.  Additionally, the team has used the Gemini South
telescope in Chile to obtain a detailed spectrum of an echo of
light from an ancient supernova that enables them to identify
the original star’s cause of death. More in NOAO Press Release
06-02.  Credit: P. Marenfeld and NOAO/AURA/NSF