I recently signed up for the Scientific American Daily Digest, and contrary to my fears of it being pseudo-spam it is instead turning out to be actually quite interesting.
Today edition includes news on the discovery of what is possibly the record holder as youngest supernova remnant in our own galaxy: G1.9+0.3. Its more interesting as given the estimated supernova rate in the Milky Way there should be of order ten young remnants (young being younger than Cas A, which is about 300 years old).
A Chandra X-ray Observatory press release on G1.9+0.3 can be found here, which is also the source of the images shown to the top left of this post. There is also a nice map showing the location of famous SNRs with respect to our location in the Milky Way.
Note that "age" is measured as time since we would have seen the SN explosion (if dust and gas wasn't in the way) and not true "absolute" age. In terms of true age Cas A happened over 11000 years ago and this new object, being more distant, happened even before that, about 25000 years ago.
Think that is confusing? How about people with different languages perceiving colors differently? It happens, even though the colors are truly the same. Now the argument is about how babies perceive color before the learn language.
[update: Whoops, no title! Thanks to Jason Harris for pointing that out.]