There is a Norse myth about 12 gods having a dinner party at Valhalla, their heaven. In walked the uninvited 13th guest, the mischievous Loki. Once there, Loki arranged for Hoder, the blind god of darkness, to shoot Balder the Beautiful, the god of joy and gladness, with a mistletoe-tipped arrow. Balder died and the Earth got dark. The whole Earth mourned.
There is a Biblical reference to the unlucky number 13. Judas, the apostle who betrayed Jesus, was the 13th guest to the Last Supper.
A particularly bad Friday the 13th occurred in the middle ages. On a Friday the 13th in 1306, King Philip of France arrested the revered Knights Templar and began torturing them, marking the occasion as a day of evil.
In ancient Rome, witches reportedly gathered in groups of 12. The 13th was believed to be the devil.
Both Friday and the number 13 were once closely associated with capital punishment. In British tradition, Friday was the conventional day for public hangings, and there were supposedly 13 steps leading up to the noose.
It is traditionally believed that Eve tempted Adam with the apple on a Friday. Tradition also has it that the Flood in the Bible, the confusion at the Tower of Babel, and the death of Jesus Christ all took place on Friday.
Numerologists consider 12 a "complete" number. There are 12 months in a year, 12 signs of the zodiac, 12 gods of Olympus, 12 labors of Hercules, 12 tribes of Israel, and 12 apostles of Jesus. In exceeding 12 by 1, 13's association with bad luck has to do with just being a little beyond completeness.
And there's more.
More than 80 percent of high-rises lack a 13th floor.
Many airports skip the 13th gate.
Airplanes have no 13th aisle.
Hospitals and hotels regularly have no room number 13.
Italians omit the number 13 from their national lottery.
On streets in Florence, Italy, the house between number 12 and 14 is addressed as 12 and a half.
Many cities do not have a 13th Street or a 13th Avenue
In France, socialites known as the quatorziens (fourteeners) once made themselves available as 14th guests to keep a dinner party from an unlucky fate.
Many triskaidekaphobes, as those who fear the unlucky integer are known, point to the ill-fated mission to the moon, Apollo 13.
If you have 13 letters in your name, you will have the devil's luck . Jack the Ripper, Charles Manson, Jeffrey Dahmer, Theodore Bundy and Albert De Salvo all have 13 letters in their names.
Here in sunny Arizona, it's a typical Friday the 13th day. I woke early and suddenly this morning with what sounded like two gunshots. When I got out of bed, both cats were acting nervous and looking toward one side of the house, where there is a sunporch with windows. I looked and looked but saw nothing. No police cars. No bodies. Nothing.
Nothing that is except a very grey day with wet streets indicating a light rain had fallen. Nothing else. One might say "a perfect Friday the 13th day."
All historical trivia courtesy of http://www.corsinet.com/trivia/scary.html#friday