A period of 28 days or the mark of the end of a 28-day lunar cycle, which also happens to be the same as a woman's fertility cycle.

13 moonths fit exactly into one year. In pagan times, at the end of the 13th moonth it would be time for the King to be sacrificed and for the Queen to select a new man to be her King. The King's blood had to be poured into the ground to make the earth fertile again and the harvest plentiful, which is why they say that the number '13' is the 'unlucky number'.
"What on earth is going on out there?"

"Winter solstice blue moonth. Some poor bastard's going to be sacrificed so that the earth may bear fruit."

"Seems a bit rough on the bloke."

"That's what I said, but I obviously wasn't taking into account 4000 years of patriarchal tyranny."
by Stefanowicz October 2, 2007
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