The brightest radio source in the sky other than the Sun, identified as the remnant of a supernova that must have occurred around AD 1667. No records exist of any observation of a supernova at this time. It is assumed that it was obscured by large quantities of dust lying in the line of sight to the object, which is 10,000 light years away. The radio emission is concentrated in a ring-like shape 4 arc minutes in diameter, suggesting a shell of material ejected in an explosion, and some faint nebulosity can be detected in optical photographs of that region of the sky. X-ray emission is also detected in the same ring shape.