Or, “Fear of Friday the thirteenth,” as it is more commonly known.
Congratulations, superstitious people! Today is Friday the 13th! Since it’s December, it’s the second Friday the 13th this year. Next year, there will only be one Friday the 13th, in June. That’s because next year starts on a Wednesday, and it’s not a leap year – if it was a leap year, there would be two Friday the 13ths (March and November). If a year starts on a Monday, there will be two Friday the 13ths, if it starts on a Friday or Saturday, there will be one. If a normal year starts on a Sunday or Tuesday, there will be two, if it starts on a Wednesday there will be one, and if it starts on a Thursday there will be three. If a leap year starts on a Tuesday there will be one Friday the 13th, if on a Wednesday or Thursday there will be two, and if on a Sunday, three. There are an average of 12 Friday the 13ths in any seven-year cycle, and an average of 1.7 Friday the 13ths in any given year.
There wasn’t really a superstition about Friday the 13th being unlucky until the middle of the 19th Century, and is only considered unlucky in the first place because 13 is an unlucky number (it’s the sixth prime, a 13th short month is needed to fit the 12 lunar months into a solar year, there were 13 people at the last supper, and so on), and Friday is also apparently unlucky (the only reason I can find that the day might be considered unlucky is that Jesus was crucified on a Friday). The fact that Phillip IV of France launched a purge of the Knights Templar on Friday the 13th in the early 14th Century is apparently a modern correlation, and possibly invention as well.
I’m only mildly superstitious, and I don’t give much weight to Friday the 13th being a day of bad luck. Thirteen is, perhaps, unlucky, for reasons totally unrelated to those I gave above, but could only apply to me and my immediate family. There is no logical reason to think that bad things will happen just because of a labelling convention that isn’t even practised by the whole world, let alone considered unlucky by the whole world.