Friday the 13th

The fear of Friday the 13th is called paraskavedekatriaphobia, a word derived from the concatenation of the Greek words Paraskeví (Παρασκευή) (meaning Friday), and dekatreís (δεκατρείς) (meaning thirteen), attached to phobía (φοβία) (meaning fear). The term is a specialized form of triskaidekaphobia, a simple phobia (fear) of the number thirteen appearing in any case. Thirteen may be considered a "bad" or "unlucky" number simply because when a group of 13 objects or people is divided into two, three, four or six equal groups, there is always one leftover, or "unlucky", object or person.According to another interpretation, the number 13 is unlucky because it is the number of full moons in a contemporary year, but two full moons in a single calendar month (mistakenly referred to as a blue moon in a magazine article of the 1940s) only happens about every 5 years. Early nursery rhymes stated there were thirteen months in a year because of the natural moon cycle that was used to count the lunar year. In England, a calendar of thirteen months of 28 days each, plus one extra day, known as "a year and a day" was still in use up to Tudor times.Another hypothesis about the origin of Friday the 13th as an unlucky day is attributed to this being the day that the Knights Templar were slaughtered in a collaboration between King Philip IV of France and Pope Clement V finishing with the burning at the stake of Jacques De Molay.