While talking about the meaning of comets moving against the order of the signs (like the comet Lulin)- in his comment to Tetrabiblos – Girolamo Cardano explains why this is so a bad omen, with reasons unfortunately very true for present time.
This means heresy and perturbation in religions, because men can make evil in everything but especially in wars of religion, when they perform the cruelest violence against children and infants, and kill with their crusades, and make slaves their prisoners, destroy fields, some men believe to obey God, others make believe.
Heaven astrolabe: Traditional, hellenistic & medieval astrology 