This Friday is the thirteenth day of the month of October; it is known as "Friday the Thirteenth." In many cultures, Friday the 13th is considered an unlucky day and many people avoid travel and other dangerous activities on this day to avoid the curse of the day. The clinical name for the illness stemming from fear of Friday the Thirteenth is "paraskavedekatriaphobia." In general, many cultures view the number thirteen itself as an "unlucky" number, which accounts for the lack of a "thirteenth" floor in tall buildings, thirteenth apartment in apartment complexes, and other missing 13's. The source of the superstitious belief surrounding the number thirteen, Friday, and Friday the Thirteenth are numerous, but mainly point to the same source: The Church.
Some explain that the origin of this phobia of Friday the thirteenth is Christian in nature. These scholars understand that the source of the bad occurrences, which happen on days associated with the number thirteen, is the fall of the Christian Eastern Roman (Byzantine) Empire centered in Constantinople to the Turks in 1453. The sum of all the digits in the year 1453 is 13, which is supposedly the source for the superstitions about Friday the thirteenth. However, even the Turks so disliked the number 13 that it "was practically expunged from their vocabulary". Others note that thirteen is a number associated with witches (e.g. the ancient Roman accusation that witches always travel in groups, covens, of thirteen an idea which Wiccans have recently revived) and pagans, and the superstitions surrounding the number outdate Christianity: The Mesopotamian Code of Hammurabi omits 13 in its numbered list of laws. This implies that even then there was a superstition against referring to the number thirteen. Perhaps the Christians later adopted this superstition from the ancient Mesopotamians and Christianized it in the same that they Christianized the Viking belief that Loki was the 13th god the Norse pantheon into the Christian belief that Satan was the 13th angel and that Judas was the 13th guest at the Last Supper.
Some conspiracy theorists say that the superstitions associated with Friday the Thirteenth stems from the fact that the Knights Templar were arrested and murdered by King Philip IV of France on Friday 13th October, 1307. The later successors to the Knights Templar, the freemasons, also used the number thirteen as an especially symbolic number. According to some conspiracy theorists, the United States of America was established by freemasons, and Masonic icons were secretly introduced into America culture. There were originally thirteen colonies which unified to eventually create the United States of America. While some say that the number of colonies explains the uncanny coincidences of the numerous instances of the number thirteen in the Great Seal of the United States. In the Seal, there are 13 levels of the truncated pyramid, 13 letters in the phrase "E Pluribus Unum", 13 letters in the phrase "Annuit Coeptis", 13 stars above the Eagle, 13 leaves on the olive branch, 13 olives on the olive branch, 13 arrows held by the Eagle, and 13 bars on the shield.
Some explain that the fear of the number thirteen, Triskaidekaphobia is simply because thirteen is a prime number. However, this does not justify the fear of the number, so others explain that it is because 13 is the number which directly follows the popular number 12. Twelve is a popularly used number in many cultures because it is a highly composite number as it is divisible by 1; 2; 3; 4; 6; and 12. According to Thomas Fernsler, an associate policy scientist in the Mathematics and Science Education Resource Center at the University of Delaware, numerologists consider 12 a "complete" number. There are twelve months in a year, signs of the zodiac, tribes of Israel, and apostles of Jesus. "In exceeding 12 by 1, Fernsler said 13's association with bad luck 'has to do with just being a little beyond completeness. The number becomes restless or squirmy'."
Other historians suggest that the Christian distrust of Friday the Thirteenth is actually linked to the early Catholic Church's overall suppression of both pagan religions and women. According to the Roman calendar, Friday was the day of Venus, the goddess of Love. When the Vikings accepted the calendar, they renamed the day after Frigg, or Freya—thus the name "Friday" for Frigg's Day or Freya's Day—the Norse goddesses connected of love and sex. Both of these strong female figures once posed a threat to male-dominated Christianity, which celebrated celibacy and viewed sex as inherently evil. According to this theory, the Christian church vilified the day named after these gods. Furthermore, the number thirteen is reminiscent of the thirteen menstrual cycles which a woman goes through in the period of one year, an "impure" element of life which the Church leaders wished to downplay. Additionally, Friday was known as the "Witch's Sabbath", so the Church leaders reasoned that if it is a holy day for pagans, it must be unholy for Christians.
The Church used theological reasons and Biblical references in saying that Friday is an unlucky day. It is well known that Christians believe that Friday was the day that Jesus was crucified. Another tragedy which occurred on Friday was that Eve tempted Adam to eat from the Forbidden Fruit. There is also a belief that Abel was slain by Cain on Friday the 13th, although this assertion is unbased. This is because Abel was born on a Friday and lived for either fifty or ninety days, neither of which would have caused his day of death to have been on another Friday. Some assert that the Great Flood began on a Friday; however, this assertion is also unfounded.
Although the fear of Friday, Thirteen, and Friday the Thirteenth is often unjustified, there was some reason to fear the day. In Britain, as well as in Ancient Rome, Friday was known as "Hangman's Day" because that was when those condemned would be executed by being hanged. Tradition says that there were thirteen steps to the platform from where one would be publicly hanged. In more recent times, the tragedy of Apollo 13, the thirteenth mission in the Apollo space program, gave people reason to believe in the superstitious powers of the number 13. Furthermore, popular culture rooted in movies like Friday the Thirteenth, fuels the global phobia of Friday the Thirteenth. Despite the irrational nature of the fear of Friday the Thirteenth, many people refrain from work and travel on that day. Experts estimate hundreds of millions of dollars in lost revenue result from the phobia of Friday the Thirteenth. Journalists report that the fear of Friday the Thirteenth and the number thirteen is very powerful in the real estate sector. This fear of 13 is so strong in that, according to Dr. Donald Dossey, founder of the Stress Management Center and Phobia Institute in Asheville, North Carolina, more than 80 percent of high-rises lack a 13th floor. Many airports skip the 13th gate and hospitals and hotels regularly have no room number 13. On streets in Florence, Italy, the house between number 12 and 14 is addressed as 12 and a half, a similar phenomenon is seen in the United States whereby the house or apartment is sometimes numbered 12A. In French society, socialites known as quatorziens (fourteeners) were for hire to serve as 14th guests to a dinner party, because having exactly thirteen people at a meal was considered to cause unlucky fate.
Despite the fact that many gentiles consider the number 13 to be unlucky, for Jews it is considered a specifically auspicious number. Until the end of one's thirteenth year of life, one's Evil Inclination does not have any force within a boy, but once a man passes his thirteenth birthday, he becomes a Bar Mitzvah because from then on his soul has an inclination to do both evil and good. When Moses prayed to G-d for His forgiveness after the Jews' sinned with the Golden Calf at Mount Sinai, G-d taught Moses that if prayers are accompanied by a description of G-d's Thirteen Attributes of Mercy, then that prayer will not be returned empty-handed. The Talmud maintains a tradition that no tribe of the Israelites will ever be completely wiped out. Rabbeinu Yishmael Ben Chachamon explains that the twelve tribes of the Jewish nation are compared to the stars of the zodiac constellations. Later in the same chapter, the Talmud says that in the future, the land of Israel will be divided into thirteen portions, not twelve as it was before. Seeing how there are only twelve tribes, the Talmud understands that the thirteenth portion will belong to the monarch of the United Israel Kingdom. Perhaps one can say that this thirteenth element is represented in the Zodiac by Ophiuchus, which is a Zodiacal constellation but is not counted as an astrological sign. When penning the most basic creed of Judaism for simplification purposes, Maimonides decided to write Thirteen Articles of Belief (ani ma'amin) to show the significance of the number thirteen.
Whether or not the fears concerning Friday the Thirteenth are legitimate, it is still forbidden for a Jew to believe in such superstition. Leviticus 19:26 clearly says "You shall not believe in lucky times." Divination based on past or future events is forbidden by Torah law. The Talmud and Midrash explain that the prohibition says that one is not allowed to say "such-and-such day is a good day to start working" or "such-and-such hour is a bad time to go outside." This prohibition is again repeated in Deuteronomy when the Torah says that a person who commits such an act should not be found in the midst of the Jewish nation. Rabbi Abraham Ibn Ezra (1092-1167) explains that these people would look into the clouds and base their predications of when lucky or unlucky times will occur based on what they see in the clouds. The Sefer HaChinuch says that one has violated this prohibition if one tells another about a lucky or unlucky time, or if one schedules his actions or work based on the predictions of lucky or unlucky times. All such divination is forbidden by Halacha, and it is therefore illegal for any Jew to tell another about Friday the Thirteenth or to arrange one's actions differently because of that day.
 "Dictionary of Phrase and Fable" by Dr. Ebenezer Cobham Brewer, s.v. "Thirteen"
 "Friday the 13th Phobia Rooted in Ancient History" by John Roach, National Geographic News, August 12, 2004
 See later
 "How Friday the 13th Works" by Tom Harris, Howstuffworks.com
 Sanhedrin 38b
 See Sefer HaDoros, Year 1
 Holiday Folklore, Phobias and Fun: Mythical Origins, Scientific Treatments and Superstitious 'Cures' by Dossey, Donald E. (Outcome Unlimited Press, 1992)
 "Number 13- Unlucky As Ever" by Ben Flanagan , The Observer, January 12, 2003
 See Exodus 34:5-7
 Bava Basra 116b
 Bava Basra 122a
 Sanhedrin 65b
 Sifra 6:2 and Pesikta Zutrisa
 Mitzvah #250