The striking object appeared as bright as Saturn in the vicinity of the constellation Cassiopeia, and historical chronicles from China and Japan recorded it as a “guest star.”

Chinese astronomers used this term to signify a temporary object in the sky, often a comet or, as in this case, a supernova — a cataclysmic explosion of a star at the end of its life.

The object, now known as SN 1,181, is one of a handful of supernovas documented before the invention of telescopes, and it has puzzled astronomers for centuries.