Not that we at EarthSky suffer from friggatriskaidekaphobia – an irrational fear of Friday the 13th – but there are a number of seeming coincidences involving the number 13 this year. Did you know that exactly 13 weeks from this Friday was a Friday, January 13? And that exactly 13 weeks from now we’ll have a Friday, July 13?
Scared of Friday the 13th? An irrational fear of this date is called friggatriskaidekaphobia (Frigga is the Norse goddess for whom Friday is named)… The fact is that any leap year starting with a Sunday will have a Friday the 13th in January, April and July. Leap years starting with Sundays are the only years in which you’ll find this exact combination of three Friday the 13ths, spaced at exactly 13 weeks apart in the same calendar year, in January, April and July… How often does the January-April-July Friday the 13th trilogy repeat?
Not often. It happens only three to four times every century. It last happened in 1984 and will happen next in 2040. Throughout the 20th and 21st centuries, we get a January-April-July Friday the 13th in cycles of 28 years. That 28-year cycle, by the way, isn’t mysterious either. Days and dates generally always realign every 28 years. Again, a calendar quirk…
Gioachino Rossini, a 19th century Italian composer. Folklorists say there’s no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards‘ 1869 biography of Rossini… If a leap year of 366 days always took place every four years, ad infinitum, then we’d see the repetition of the January-April-July Friday the 13th cycle every 28 years, ad infinitum. But alas, by the Gregorian calendar rules, every centennial year not equally divisible by 400 is a common year of 365 days. That means the years 2000 and 2400 are leap years, but that 2100, 2200 and 2300 are common years… As magical as all of this number play seems to be, it’s not supernatural. The Friday the 13th calendar intrigue is simple numerology, even if it forever haunts our uncomprehending minds.
Friday the 13th Origins – Urban Legends –