Map showing a faint star recorded as 3 Cas in the constellation Cassiopeia by British astronomer John Flamsteed (1646-1719). This 3 Cas could have been a sighting of the Cassiopeia A is a glowing high-energy mass of gas and dust has been expanding for 350 years after the star that formed it exploded in a supernova. Map published in 1776 edition of Jean N. Fortin's 'Atlas Celeste de Flamsteed', a French edition of the posthumous 1729 atlas by John Flamsteed.