What you learned in school
For centuries, astronomy and general education taught that comets were omens of disaster, war, plague, or death. Students learned historical examples of comets preceding major calamities and political upheavals. Even as astronomy became more scientific, comets were still presented in textbooks as mysterious, dangerous phenomena that could foretell earthly disasters. This astrological interpretation persisted well into the scientific age.
What we know now
For centuries, textbooks and teachings presented comets as omens of disaster, war, or death. Students learned historical examples of comets preceding plagues or political upheavals. Even as astronomy became more scientific, comets were still presented as mysterious and potentially dangerous. Modern astronomy has identified comets as "dirty snowballs" - collections of ice, rock, and dust from the outer solar system. While they can pose collision risks, they're understood as natural solar system objects following predictable orbits, not supernatural omens.