Friday the 13th is considered an unlucky day in Western superstition. It occurs when the 13th day of the month in the Gregorian calendar falls on a Friday, which happens at least once every year but can occur up to three times in the same year. The fear of 13 dates back centuries and many believe it originates from the Code of Hammurabi which reportedly left out a 13th law from its list of legal rules. The number 13 has also been regarded as unlucky in certain cultures throughout history. The superstition around Friday the 13th is an example of magical thinking, where someone believes there is a causal relationship between two things that are otherwise unrelated.

Here are some interesting facts about Friday the 13th:

• The shortest period that occurs with a Friday the 13th is just one month, from February to March in a common year starting on Thursday.
• While Friday the 13th may feel like a rare phenomenon, our Gregorian calendar means that the 13th of any month is slightly more likely to fall on a Friday than any other day of the week.
• In Greece and Spanish-speaking countries, it is Tuesday the 13th that is considered a day of bad luck, while in Italy, it is Friday the 17th that is met with fear.
• Fear for Friday the 13th may have been amplified by the slasher-movie series, but the superstition has been around for centuries.

In conclusion, Friday the 13th is a day that is considered unlucky in Western superstition. It occurs when the 13th day of the month in the Gregorian calendar falls on a Friday. The fear of 13 dates back centuries and many believe it originates from the Code of Hammurabi. While the superstition around Friday the 13th may have been amplified by popular culture, it has been around for centuries and is an example of magical thinking.