Comets are also called broom stars, because when comets move, there will be a tail behind them, which is shaped like a broom star. In modern times, we call people who bring bad luck to others as broom stars, and the ancients also thought comets were unlucky.

That's a saying spread in ancient times. At that time, because of people's ignorance, people saw the comet and thought that it was shaped like a broom and had the unlucky meaning of "broom star", so they thought that seeing the comet meant bad luck.

Seeing a comet doesn't mean a disaster. It's just a natural phenomenon. People didn't understand it in ancient times, so it's far fetched. But nothing happens when you see a comet. Modern astronomers point out that a comet flying to the earth is a normal cosmic phenomenon.

Source: @antimaterias