Light echoes have also been used to study the supernova that produced the supernova remnant Cassiopeia A.[6] The light from Cassiopeia A would have been visible on Earth around 1660, but went unnoticed, probably because dust obscured the direct view. Reflections from different directions allow astronomers to determine if a supernova was asymmetrical and shone more brightly in some directions than in others. The progenitor of Cassiopeia A has been suspected as being asymmetric,[8] and looking at the light echoes of Cassiopeia A allowed for the first detection of supernova asymmetry in 2010.[9]