The ancients regarded comets as harbingers of disaster.
Tips
history
In imperial Chinese astrology, sudden new lights in the sky — 彗星 (comets) and 客星 ("guest stars," what we now call supernovae) — were read as 灾星, signs of impending calamity. Court astronomers were required to report sightings immediately.
usage
Modern figurative use parallels English "jinx": a person, team or object whose presence seems to bring bad luck.