When I was in elementary school, my teacher told my class that the full moon makes people crazy. She said it was caused by the gravitational tug of the moon on the Earth—the same forces that cause high and low tides—the argument being that our bodies are more than 60% water. I was impressionable and fascinated by weird science—who isn't at that age?—and have long since stored that "fact"oid in my ever-developing hippocampus. The full moon last week (which, not to mention, was GINORMOUS—did anyone else notice?) reminded me of this theory and made me want to do a little research of my own. Does the full moon really do something to our brains? 

Firstly, we must be on the same page as to what a "full moon" really means. The moon revolves around the Earth, and the Earth revolves around the sun. The phases of the moon simply represent the portions illuminated by the sun. All of this motion creates a very dynamic display for us earthlings. So when you see that little sliver in the sky, the rest of the moon is still there—the sun's rays just aren't reflected on the surface we're seeing.

That being said, why would an illuminated moon have some sort of effect (on tides, craziness, etc.), while a shadowed moon wouldn't?

Here's where the "science" comes in.

A 1985 meta-analysis review of 37 studies regarding moon phase and lunacy (including mental hospital admissions, hotline crisis calls, psychiatric disturbances, and criminal offenses) found no statistically significant relationships between the full moon and human behavior.

Sleep disturbances have been reported in response to a full moon. A 1999 hypothesis details how the additional outdoor lighting may contribute to sleeplessness.

We should, perhaps, turn to the animal world to see how some non-self-conscious beings react to the full moon. A study on Azara's owl monkeys found them prowling the Argentinean forests more actively on full moon nights; the poor things will actually sleep in late the next morning, not unlike your average teenager.

Interestingly, a hypothesized light-sensitive protein in Acropora millepora corals may account for their synchronous spawning for a few nights every year just after the full moon. (Good thing humans don't carry that gene.)

It also appears that prey are less active during the full moon, as the additional light makes them more visible to predators.

Light, of course, can do crazy things to our circadian rhythm. So that has to be it, right? The full moon isn't causing, like, mini gravitational tides in our watery bodies. It's messing with our heads, somehow. Truth be told, we're likely just being paranoid and superstitious. Or perhaps those who claim lunacy are those who transform into werewolves a couple times a year.

Photos courtesy Saananaveri and Wikipedia.

Fernández-Duque E, de la Iglesia H, & Erkert HG (2010). Moonstruck primates: owl monkeys (Aotus) need moonlight for nocturnal activity in their natural environment. PloS one, 5 (9) PMID: 20838447

Levy O, Appelbaum L, Leggat W, Gothlif Y, Hayward DC, Miller DJ, & Hoegh-Guldberg O (2007). Light-responsive cryptochromes from a simple multicellular animal, the coral Acropora millepora. Science (New York, N.Y.), 318 (5849), 467-70 PMID: 17947585

Raison CL, Klein HM, & Steckler M (1999). The moon and madness reconsidered. Journal of affective disorders, 53 (1), 99-106 PMID: 10363673

Rotton, J., & Kelly, I. (1985). Much ado about the full moon: A meta-analysis of lunar-lunacy research.Psychological Bulletin, 97 (2), 286-306 DOI: 10.1037//0033-2909.97.2.286

Sábato MA, de Melo LF, Magni EM, Young RJ, & Coelho CM (2006). A note on the effect of the full moon on the activity of wild maned wolves, Chrysocyon brachyurus. Behavioural processes, 73 (2), 228-30 PMID: 16814488