In 1181, a new star shone near the Cassiopeia constellation for six months before disappearing. This event, recorded as a “guest star” by Chinese and Japanese observers almost a millennium ago, has puzzled astronomers for centuries. It is one of a few supernovae to be documented before the invention of telescopes. In addition, it remained an “orphan” the longest, meaning that none of the celestial objects visible today could be assigned to it.