The everyday word is
彗星 (comet) — that's where you meet
彗 in modern STEM writing. The colloquial nickname is
扫帚星 ('broom-star'), which preserves the character's original sense: a broom or whisk. Calling a person
扫帚星 is an old curse meaning 'jinx / bringer of bad luck' — never use it of a real person.