Having looked up Friday 13th some time back there really is no conclusive evidence as to where it really eventuated, there are lots of possibilities the number 12 is a number of Completeness,12 hours on the clock, 12 Month in a year 12 signs of the Zodiac 12 Gods of Olympus and many more, Christs disciples at the Last Supper numbered 13 and that has since seemed to signify that one of the group would die its amazing how we still manage to be wary of both the number 13 and Fridays, Christ was Crucified on a Friday that then became a bad day,then when put together they are almost deadly, I know I always rethink things for that day even if only for a minute we are creatures of habit.
As for the Full Moon and if that should fall on Friday 13th Aaagghhh dread to think about that, then of course if you should be out on Friday 13th and there happens to be a full moon and your neighbour has had to get on the roof and fix the aerial be careful to walk around the ladder and please avoid the Black Cat that is about to stray across your path.
If by chance you on this same day have broken a mirror spilt the salt or even refused to buy pegs off the local Gypsies then Please I beg you lock yourself in the closet and stay there till Saturday the 14th.
One good thing the 13th in July falls on a Monday Yeah we are safe.