3 Cassiopeiae (3 Cas) is a hypothetical star in the Cassiopeia constellation catalogued by English astronomer John Flamsteed. It bears no identity with actual stars observed today. Unlike 34 Tauri, which was the planet Uranus, 3 Cas was not reconciled by later knowledge.
Read more about 3 Cassiopeiae: Identity As Cassiopeia A Supernova, Identity As Erroneous Data