Q&A: Supernova Remnants and Neutron Stars

Q:
I saw a photo designated Cas A that is labeled as a 320 year old event from a location 10,000 light years away. I was wondering how the event could have happened 320 years ago and the radiation that produced the image arrive in time for me to view it. Have I misread the caption?

A:
We have a special section explaining the age of Cas A. Try http://chandra.harvard.edu/photo/1999/0237/age.html