I Didn’t Know That. . .

Q: Why is Friday the 13th considered unlucky?

A: To understand 13, one has to understand 12. The number 12 has traditionally represented completeness. There are, for example, 12 months in the year, 12 gods of Olympus, 12 signs of the zodiac and 12 disciples of Jesus. Thirteen, then, is traditionally the symbol of the first departure from completeness, and the first step toward evil. Judas Iscariot was the 13th disciple, and the 13th tribe of Israel was the only tribe left without land.

Friday is also ill-fated. According to the Bible, Eve gave the apple to Adam on Friday and the great flood began on a Friday. Execution day in ancient Rome was Friday. Jesus was crucified on a Friday. Over time, the confluence of these separate ideas led to the idea that Friday the 13th was particularly unlucky--an idea that is, of course, without any rational foundation whatsoever. Because of the unequal lengths of months in our Gregorian calendar, the 13th falls on Friday more than any other day--about three extra times in each 400-year period, according to mathematician John Conway of Princeton.