From Answers.com:
The convergence of two superstitions between the number 13 and Friday seem to be at the heart of many questions concerning this particular superstition. So lets start with those.
FRIDAY has been an inauspicious day for a very long time, and in many varied cultures. It has been held to be both unlucky and as a day when evil influences are at work.
In Ancient Rome, Friday was execution day.
In some pre-Christian Religions Friday was a day of worship, so those who involved themselves in secular or self-interested activities on that day were not likely to receive the blessings of the gods on their undertakings. Which may go a long way to explain the superstition of not embarking on journeys or starting important projects on Fridays.
From the Christian bible:
- Friday is reputed to be the day Eve gave Adam the apple.
- It is said to be the day Adam & Eve were expelled from the Garden of Eden.
- Friday is also reputed to be the day they (Adam & Eve) died.
- The Great Flood is supposed to have started on a Friday.
- God was said to have struck the builders of the Towel of Babel and created the confusion of many tongues, on a Friday.
- The Temple of Solomon was destroyed on a Friday.
- Christ was crucified and died on a Friday.
In Britain, Friday was customarily Hanging Day.
It is said accidents are more common on Fridays, however, that may be more because Friday is the end of the work week and people are hurrying to get away from work, than any sinister reasons.
It is supposed that witches favour Friday for coven gatherings. This Pagan association was not lost on the early Christian Church, which went to considerable lengths to suppress them. If Friday was a holy day for “heathens” the Church fathers felt it must not be so for Christians, hence in the middle ages Friday became known as the “Witches’ Sabbath.”
The name “Friday” is derived from the Norse goddess known either as Frigg – wife of Odin (the goddess of marriage & fertility, the moon & witches) or Freya (goddess of love, beauty, sensuality, war, good fortune, magic & wisdom). To complicate matters the two goddesses are combined and used interchangeably by many, however, the etymology of Friday has been given both ways.
Pre-Christian Teutonic people actually considered Friday to be lucky, particularly for wedding, because of its association with the aforementioned goddesses. This however changed when the Christian church came into ascendancy. Frigg/Freya was re-cast in folklore as a witch and her day became associated with evil doings.
Various legends developed in that vein, one however, is of particular interest:
As the legend goes, the witches of the north used to observe their Sabbath by gathering in a cemetery in the dark of the moon. On one such occasion the Friday goddess, (Freya herself) came down from her sanctuary in the mountaintops and appeared before the group, who numbered only twelve at the time, and gave them one of her cats, after which the witches’ coven, and, by “tradition,” every properly-formed coven since, is comprised of thirteen members.
