Get 13 Freaky Friday the 13th Facts

If the day freaks you out, you may have paraskavedekatriaphobia, also known as friggatriskaidekaphobia—the scientific terms for fear of Friday the 13th. Triskaidekaphobia is fear of the number 13.

Mark Twain once was the 13th guest at a dinner party. A friend warned him not to go. Twain later told the friend, "It was bad luck" because they only had food for a dozen. Superstitious diners in Paris can hire a "quatorzieme," or professional 14th guest.

No one is quite sure why the day became associated with bad luck. The connection may be biblical, given that the 13th guest at the Last Supper betrayed Jesus. His crucifixion was the next day, which was, apparently, a Friday. 

The next year that will feature three Friday the 13ths is 2015. They'll be in February, March and November.

If expect your Friday the 13th to be good, be glad you aren't a 14th-century Knight Templar. On Oct. 13, 1307, officers of King Philip IV of France raided the homes of thousands of these Crusades warriors, imprisoning them on charges of illegal activities. Though the charges weren't proven, more than a hundred died of terrible torture, according to "Tales of the Knights Templar" (Warner Books, 1995).

Fittingly, director of psychological thrillers Alfred Hitchcock was born on the 13th. Friday, Aug. 13, 1999, would have been his 100th birthday. Perhaps aptly titled "Number 13," a film that was supposed to be Hitchcock's directorial debut never made it past the first few scenes and was shut down due to financial problems. He reportedly said the film wasn't very interesting.

Why does the Friday the 13th superstition stick so firmly in our minds? According to Thomas Gilovich, who chairs the department of psychology at Cornell University, our brains are almost too good at making associations.

"If anything bad happens to you on Friday the 13th, the two will be forever associated in your mind, and all those uneventful days in which the 13th fell on a Friday will be ignored," Gilovich said in a statement.

For pagans, 13 is actually a lucky number. It reflects the number of full moons in a year.

Hotels, hospitals and other high rises often skip the 13th floor, and even airports sometimes quietly omit gate No. 13.

President Franklin D. Roosevelt is said to have avoided travel on the 13th day of any month, and would never host 13 guests at a meal. Napoleon and President Herbert Hoover were also triskaidekaphobic, with an abnormal fear of the number 13.

This fear of Friday the 13th can be serious business, according to the Stress Management Center and Phobia Institute in Asheville, N.C., which, among other things, offers therapy to help people overcome their fear of the freaky friday. Their estimates suggest hundreds of millions of dollars, up to $900 million are lost due to people's fear of flying or doing the business as usual that day, though that number isn't backed up with other estimates.