What’s all the fuss about Friday 13th:

• In order to organize time, human beings created calendars.

• As part of today's dominant calendar system, every year is divided into 12 periods called months, consisting of roughly 30 days each.

• All days are also grouped into sets of seven, called weeks.

• In the Western world, a significant chunk of the population suspects bad things will happen whenever the 13th day of a month occurs on the day of the week called Friday.

Like many human beliefs, the fear of Friday the 13th (known as paraskevidekatriaphobia) isn't exactly grounded in scientific logic. But the really strange thing is that most of the people who believe the day is unlucky offer no explanation at all, logical or illogical. As with most superstitions, people fear Friday the 13th for its own sake, without any need for background information.

The superstition does have deep, compelling roots, however, and the origins help explain why the belief is so widespread today. Let's look at some of the interesting stories behind this unluckiest of days.

The fear of Friday the 13th stems from two separate fears -- the fear of the number 13 and the fear of Fridays. Both fears have deep roots in Western culture, most notably in Christian theology.

Thirteen is significant to Christians because it is the number of people who were present at the Last Supper (Jesus and his 12 apostles). Judas, the apostle who betrayed Jesus, was the 13th member of the party to arrive.

Sailors were particularly superstitious in this regard, often refusing to ship out on a Friday.

According to unverified legend (very likely untrue), the British Navy commissioned a ship in the 1800s called H.M.S. Friday, in order to quell the superstition. The navy selected the crew on a Friday, launched the ship on a Friday and even selected a man named James Friday as the ship's captain. Then, one Friday morning, the ship set off on its maiden voyage... and disappeared forever.

A similar, entirely factual story is the harrowing flight of Apollo 13.

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.

Ultimately, the complex folklore of Friday the 13th doesn't have much to do with people's fears today. The fear has much more to do with personal experience. People learn at a young age that Friday the 13th is supposed to be unlucky, for whatever reason, and then they look for evidence that the legend is true. The evidence isn't hard to come by, of course. If you get in a car wreck on one Friday the 13th, lose your wallet, or even spill your coffee, that day will probably stay with you.

But if you think about it, bad things, big and small, happen all the time.

If you're looking for bad luck on Friday the 13th, you'll probably find it.