Just about everybody has some sort of superstition. Many of us carry good-luck charms or avoid black cats. And football fans will wear the same pair of socks for a month if they think it’ll help their team.

One big superstition is today’s date: Friday the 13th. It’s been considered bad luck for a long time. But no one is sure exactly why it earned such a bad reputation.

The number 13, of course, has had evil connotations for centuries. In Scandinavian mythology, for example, a 13th god crashed a party and killed one of the other gods. And in Christianity, 13 attended the Last Supper, making the number the unluckiest of all.

Friday has had a bad rep for a long time, too. The day is named for Frigg, a Norse goddess. Christians called her a witch, and her day became the Witches’ Sabbath. And in some cultures, Friday was considered a bad day for a wedding or to start a journey.

Linking the bad mojo of Friday and the number 13 seems to have occurred in the 19th century. It was solidified by a 1907 novel, called Friday the 13th. In it, a broker takes advantage of the superstitions about the day to mess with the stock market. And the link got an even bigger boost with the series of “Friday the 13th” movies.

In reality, there’s nothing unlucky about Friday the 13th at all. It’s just another day on the calendar.

One interesting coincidence, though, is that thanks to Leap Year, there’s another Friday the 13th next March — 13 weeks from now.

Script by Damond Benningfield