There are multiple types of Supernovae that have been observed throughout the Universe.  Classifying them is difficult because the conditions of each one are not always similar.  There are now seven different classifications of these stellar explosions, that are divided (and subdivided) by their spectral characteristics.  By studying the light from supernovae, we can determine what type it is, and identify what kind of stellar environment led to its destruction. The supernova remnant 3C 397, shown above in the constellation Aquilla at a distance of 33,000 light years, has thought to have been expanding for 1-2 millennia. Originally thought to have...