From Mardi Gras Unmasked:
Though its exact origins are subject to debate, the celebration known as Carnival came to be associated with Judeo-Christian tradition. In its earliest usage in medieval Europe, the Latin word carnelevare, from which "carnival" is derived (literally meaning "to lift up" or relieve from "flesh" or "meat"), may have referred to the beginning of the Lenten season of atonement and abstinence rather than the festive holiday customs that preceded Lent. In any case, over time it became established as the season of merriment that begins on the feast of the Epiphany (Jan. 6), also known as Kings' Day or Twelfth Night (it’s the twelfth day of Christmas, the day the gift-bearing Magi visited the Christ child).
Because the day before Ash Wednesday, which marks the beginning of Lent, was one of feasting—as symbolized by the ritual slaughter of a fatted bull or ox (boeuf gras)—it came to be known as Fat Tuesday or, as the French would say, Mardi Gras. Occurring on any Tuesday from Feb. 3 through March 9, Mardi Gras is tied to Easter, which falls on the first Sunday after the full moon that follows the Spring Equinox. The climax of Carnival, Mardi Gras is always scheduled 47 days preceding Easter (the 40 days of Lent plus seven Sundays).
As a person of no religion, I like that some religious observances follow natural events, like the Vernal Equinox and a full moon. As to how my family will deal with the wildness of New Orleans during Mardi Gras? I'll let you know. Most of the big parades are a mere four houses (albeit large ones) from my own. We'll be there watching, catching beads, and sending them on to anyone who asks for them. If, If, I convince my daughters to release them from their greedy clutches. Plastic beaded necklaces, you know, are treasure.