Astronomer William Ashworth and others have suggested that the Astronomer Royal John Flamsteed may have inadvertently observed the supernova on August 16, 1680, when he catalogued a star near its position.
Three hundred years later, the American astronomical historian William Ashworth suggested that what Flamsteed may have seen was the most recent supernova in the galaxy's history, an event which would leave as its remnant the strongest radio source outside of the solar system, known in the third Cambridge (3C) catalogue as 3C 461 and commonly called Cassiopeia A by astronomers.