In the Gregorian calendar, the date occurs at least once every year. However, three of them can come together in a single year, although this only happens once in every few years. The last time it occurred was in 2009 and the next time it will occur (after 2012, of course), will be in 2015.
Interestingly, this particular year is even more special. This is the first time since 1984 that the three unlucky dates are spaced exactly 13 weeks apart! This amazing bit of coincidence won't happen again till 2040, according to Tom Fernsler, a University of Delaware math professor, who was quoted in USA Today.
Meanwhile, according to folklorists, there was no written evidence documenting the fear of the date before the 19th century. In fact, the earliest such reference is in Henry Sutherland Edwards' 1869 biography of Italian music composer Gioachino Rossini.
Here are 13 facts about the unlucky day...
1. Friday has reportedly been considered a grim day ever since the time of the 14th century book Canterbury Tales
2. According to Christian scripture and tradition, Friday is unlucky because Jesus was supposedly crucified on that day
3. Since the 1800s, several stock markets have crashed on Fridays
4. On Friday, April 13th, 2029, a near-Earth asteroid - 99943 Apophis - will swing past the Earth
5. According to biblical scholars, Eve tempted Adam to eat the fruit from the Tree of the Knowledge of Good and Evil on Friday
6. It is also believed that Adam and Eve's son, Abel, was killed by his brother Cain on Friday the 13th
7. American rapper and actor Tupac Shakur was shot four times on Sept. 7 in Las Vegas. He died on Friday, Sept. 13, 1996.
8. The fear of the number 13 is called triskaidekaphobia. The number is considered unlucky because it follows 12... considered the complete number - as in 12 months, 12 zodiac signs and 12 apostles of Jesus, amongst others incarnations
9. Six of the Friday the 13th horror films were released on Friday the 13th
10. The Ancient Romans also considered 13 unlucky. According to them, witches gathered in groups of 12... a 13th person joining them would be considered the devil.
11. In Italy, the house between numbers 12 and 14 is addressed as 12-and-a-half.
12. Many people who feared with the number 13 also point to the crash of the seventh manned mission in the U.S.'s Apollo space program - Apollo 13
13. According to Fernsler, in a 400-year period, the 13th falls on a Friday more than any other day i.e. 688 times