Ordinarily, the 13th of the month is just another day on the calendar. However, when it falls on a Friday, as it will tomorrow, the day takes on a whole new significance. That’s because Friday the 13th has a reputation for being unlucky. The unfounded fear that affects over twenty million people in the U.S., and many more worldwide, is so serious, that it is considered a medical disorder that goes by the names friggatriskaidekaphobia or paraskevidekatriaphobia.