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 outburst spectra of supernovae that exploded hundreds of years ago. This is just awesome.