Do you suffer from Friggatriskadekaphobia? If so, you might want to stay in bed a week from Friday.
Friggatriskadekaphobia is fear of Friday the 13th. In many cultures, 13 is the unluckiest number, although it is 17 in Italy. Friday is usually considered the least lucky day, although Tuesday is the unluckiest day in South America.
This is the only Friday the 13th, this year. Every year has at least one. About as many years have two as have one, both of which occur about 43 times each century. Every non leap year that begins on a Thursday — like 2015 — will contain three occurrences of Friday the 13th.This happens 14 or 15 times per century. Leap years that begin on Sunday — like 2018 — will also have three of them.
Friday falls on the 13th slightly more often than any other day of the week. The Gregorian calendar started in 1582. It made the calendar year actually match the astronomical year. It is easy to calculate the day of the week for every day of the year. In every span of 400 years, the complete Leap Year cycle, Sunday falls on the 13th 687 times, Monday 685 times, Tuesday 685 times, Wednesday 687 times, Thursday 684 times, Friday 688 times and Saturday 684 times. Occasionally, as was the case in 2007 and last year, there were two Fridays that fell on the 13th, which were 13 weeks apart. The year 2012 contained three Friggatriskadek’s separated by 13-week intervals.
Friday the 13th isn’t an uncommon occurrence. Another regular, commonly referred to interval is a month of Sundays. Thirty days make up a month, so a month of Sundays equals 30 weeks — about two-thirds of a year.
What happens “once in a Blue Moon?” A Blue Moon. A Blue Moon occurs July 31, 2015. The next one after that won’t be until Jan. 31, 2018. That year will have two Blue Moons, the second on March 31.
So Friday the 13th occurs one to three times per year, on average about six months apart, but sometimes in pairs. A month of Sundays occurs every 30 weeks, roughly seven months. Once in a Blue Moon occurs, on average, once or in a pair each two-and-a-half year period.