Friday the 13th, Flight 666 to HEL

Long considered a harbinger of bad luck, Friday the 13th has inspired a late 19th-century secret society, an early 20th-century novel, a horror film franchise and not one but two unwieldy terms—paraskavedekatriaphobia and friggatriskaidekaphobia—that describe fear of this supposedly unlucky day.

Researchers estimate that at least 10 percent of the U.S. population has a fear of the number 13, and each year the even more specific fear of Friday the 13, known as paraskevidekatriaphobia, results in financial losses in excess of $800 million annually, as people avoid marrying, traveling or in the most severe cases, even working. But what’s so unlucky about the number 13, and how did this numerical superstition get started?

5. The number 13 terrifies even the master of horror. Don’t think triskaidekaphobia is serious? The number 13 scares Stephen King, the man whose nightmares have kept people up at night for decades. “I always take the last two steps on my back stairs as one, making 13 into 12 (there were, after all, 13 steps on the English gallows – up until 1900 or so – and executions were traditionally carried out on Fridays),” he wrote in 1984, a year with three Friday the 13ths.

A full moon on Friday the 13th is spooky enough, but hold on to your black cats. September's full moon will also be a "micromoon."

Skywatchers in Central, Mountain and Pacific time zones will get a view of the full moon tonight (Sept. 13) at 11:32 p.m., 10:32 p.m. and 9:32 p.m., respectively, while East Coasters will see the moon at its fullest at 12:32 a.m. on the 14th. Regardless of time zone, the moon will appear just a bit dimmer than usual (eerie!), because it will be at apogee, or its farthest distance from Earth.

That means that the moon will appear about 14% smaller and 30% dimmer than when it is at its closest point to Earth, which is known as perigee.

The full moon that occurs closest to the autumnal equinox is called a Harvest Moon. Autumn officially begins on September 23 at 3:50 a.m. EDT.

However, this year's Harvest Moon is unlike most in that it will coincide with Friday the 13th. This rarity hasn't happened since a full moon appeared on October 13, 2000.

The next time a full moon will coincide with Friday the 13th will be August 13, 2049.