It happens at least once and at most three times a year. Any month that starts on a Sunday, like this month,  will have one.

It’s Friday the 13th.

The fear of Friday the 13th is called friggatriskaidekaphobiaFrigga, meaning “Friday” and triskaideka for 13 and the Greek phóbos for phobia or “fear”. The word itself isn’t ancient – being derived in 1911 and first appearing in a mainstream source in 1953. (*)

There doesn’t seem to be any real written evidence for a “Friday the 13th” meaning bad luck as a superstition before the 19th century.

The most popular theory is that it’s a combination of the superstition that thirteen is an unlucky number and another superstition that Friday is an unlucky day.

According to Wikipedia, looking at numerology, you find the the number 12 to be considered the number of completeness – twelve months of the year, twelve signs of the zodiac, twelve hours of the clock, twelve tribes of Israel, twelve Apostles of Jesus, twelve gods of Olympus, and so on. That makes 13 irregular, transgressing this completeness.

And poor Friday (which most of us working folks love as the end of work and the start of weekend) has been considered an unlucky day at least since the 14th century’s The Canterbury Tales.

Some people believe it is an unlucky day to undertake journeys or begin new projects. Black Friday has been associated with stock market crashes and other disasters since the 1800s. It has also been suggested that Friday has been considered an unlucky day because, according to Christian scripture and tradition, Jesus was crucified on a Friday. Add to that the 13 people at his Last Supper and you have yourself a good superstition.

Here’s another theory from Charles Panati, a leading authority on origins:

“The actual origin of the superstition, though, appears also to be a tale in Norse mythology. Friday is named for Frigga, the free-spirited goddess of love and fertility. When Norse and Germanic tribes converted to Christianity, Frigga was banished in shame to a mountaintop and labeled a witch. It was believed that every Friday, the spiteful goddess convened a meeting with eleven other witches, plus the devil — a gathering of thirteen — and plotted ill turns of fate for the coming week. For many centuries in Scandinavia, Friday was known as “Witches’ Sabbath.”

If you read The Da Vinci Code, you might recall that Dan Brown brought into the story the idea that the Knights Templar (whose mission was to protect Christian pilgrims during the Crusades) became too powerful and wealthy, and King Philip secretly ordered the mass arrest of all the Knights Templar in France on Friday, October 13, 1307 which was a Friday the 13th.

Believe what you will, but have a lucky day. And we all know that if we’re planning on watching a movie tonight, just what movie we’re supposed to watch.