Paraskevidekatriaphobia:
Fear of Friday the 13th

Friday the 13th is a day fraught with peril.  A Friday occurring on the 13th day of any month is considered to be a day of bad luck in many superstitions around the globe.

Although most of us would probably affirm that superstition's
role in Western culture is now a much diminished one, more a source of amusement than anything else, there are still those who allow their trepidation over particular days or dates to prevent them from engaging in their choice of activities.

We may make jokes about Friday the 13th and only kiddingly instruct loved ones to exercise greater care on that day, but those who suffer from a fear of the number thirteen or a fear of Friday the 13th  may genuinely feel limited by the rumored potential for ill luck connected with the date.

Similar superstitions exist in some other traditions.

In the Spanish-speaking world, it is Tuesday the 13th (as well as Tuesdays in general) that brings bad luck; a proverb runs "En martes, ni te cases ni te embarques (on Tuesday, neither get married nor start a journey)" .

The fear of Friday the 13th is called paraskavedekatriaphobia, paraskevidekatriaphobia or friggatriskaidekaphobia, a specialized form of triskaidekaphobia, a phobia (fear) of the number thirteen.

The Origin
The origin of the Friday the 13th superstition has been linked to the belief that there were 13 people at The Last Supper of Jesus, who was crucified on Good Friday, but it probably originated in medieval times.

It has also been linked to the fact that a lunisolar calendar must have 13 months in some years, while the solar Gregorian calendar and lunar Islamic calendar always have 12 months in a year.

Another suggestion is that the belief originated in a Norse myth about twelve gods having a feast in Valhalla. The mischievous Loki gate-crashed the party as an uninvited 13th guest and arranged for Hod, the blind god of darkness, to throw a branch of mistletoe at Balder, the god of joy and gladness. Balder was killed instantly and the Earth was plunged into darkness and mourning as a result.

Effects
Strangely, there is evidence to suggest that Friday the 13th is actually unlucky for some. Psychologists have found that some people are especially likely to have accidents or fall ill on Friday the 13th. This has been attributed to such people feeling a heightened state of anxiety on that day. The Stress Management Center and Phobia Institute in Asheville, North Carolina estimates that in the United States alone, $800 or $900 million is lost in business each Friday the 13th because some people will not travel or go to work.

The date is also well-known in the motorcycle (biker) community: since 1981, motorcycle enthusiasts and vendors gather every Friday the 13th in Port Dover, Ontario, Canada. This tradition started on November 13, 1981 by Chris Simons as a gathering of approximately 25 friends. The event has grown substantially, with an estimated 100,000 people attending in August 2004, as well as music bands, vendors, a bike show, etc.

Occurrence

The following months have a Friday the 13th:
* 2000 October
* 2001, 2007, 2018 April, July
* 2002, 2013, 2019, 2024 September, December
* 2003, 2008, 2014, 2025 June
* 2004 February, August
* 2005, 2011, 2016, 2022 May
* 2006, 2017, 2023 January, October
* 2009, 2015, 2026 February, March, November
* 2010, 2021, 2027 August
* 2012 January, April, July
* 2020 March, November

This sequence, here given for 2000-2027, repeats every 28 years from 1901 to 2099. The months with a Friday the 13th are determined by the Dominical letter of the year. All months whose first day falls on a Sunday will contain a Friday the 13th.

Because the Gregorian Calendar 400-year cycle has a whole number of weeks, it is not possible for exactly 1 in 7 months to have a Friday the 13th. In fact, the 13th is more likely to be a Friday than any other day of the week.

Over any given 400-year cycle the 13th day of the month occurs 4800 times. The distribution of 13th day of the month is as follows:

* Monday ( 685 or 14.27% ),
* Tuesday ( 685 or 14.27% ),
* Wednesday ( 687 or 14.31% ),
* Thursday ( 684 or 14.25% ),
* Friday ( 688 or 14.34% ),
* Saturday ( 684 or 14.25% ),
* Sunday ( 687 or 14.31% ).

This means the 13th day of the month is slightly more likely to occur on a Friday.