(supernova remnant visible for 300 years)
Cassiopeia A (or Cas A) is a supernova remnant about
11000 light-years away for a supernova that became visible
to Earth in about 1680.
It was first recorded in 1948 and has been much studied since.
Reflections of it off gas clouds have recently
provided some look at the actual event.
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Referenced by pages:
supernova remnant (SNR)