Echos of Stars Past

Two recent papers describe the detection of light echos from both Tycho's Supernova and the Cassiopeia A Supernova:

• The Cassiopeia A Supernova was of Type IIB, O Krause, et al., arXiv:0805.4557v1 [astro-ph]
• Scattered-Light Echoes from the Historical Galactic Supernovae Cassiopeia A and Tycho (SN 1572), A. Rest et al., arXiv:0805.4557v1 [astro-ph]

This means that it is now possible to study the spectra of the outbursts of supernovae that exploded hundreds of years ago. This is just awesome.