A supernova in Cassiopeia that appeared in 1572 November, and was extensively studied by Tycho Brahe. The maximum magnitude was −4, and the star remained visible until 1574 April–May. The light-curve shows that it was a Type Ia supernova. The radio source 3C 10, faint optical nebulosity, and a weak X-ray source comprise the supernova remnant, about 8000 l.y. away.