Cassiopeia is a constellation in the northern sky. It was named after a queen in Greek mythology called Cassiopeia. It looks like a letter W or M, with five bright stars that make the W or the M shape. It has two very bright stars called ρ Cas and V509 Cas.
In 1572, a supernova called Tycho's Star, or SN 1572, was seen in Cassiopeia by many people.