No, Full Moons Don't Make You Bitchy

The theory: The menstrual and lunar cycles are similar in length, and one study found nearly 30 percent of women got their period around the full moon. Cue The Twilight Zone music.

The truth: Further research showed zero connection between moon phases and your flow—which makes sense, because otherwise we'd all get our periods at the same time! The real trigger? Hormonal changes. Unsolved period mysteries do still exist though, like why cycles can differ so much (21 to 35 days) from one woman to the next. Doo-doo-doo-doo...

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The theory: Ob-gyns joke that more babies make an entrance when the moon is full—and in some ancient cultures, the moon was a fertility symbol. (Come to think of it, it does kinda resemble a pregnant belly.)

The truth: Chalk this one up to superstition, say scientists. Studies of births haven't found an uptick when the night sky is well lit. Doctors still aren't quite sure what brings on labor (aside from: not the moon). One hypothesis is that once a fetus's lungs are mature, its body releases a protein that initiates contractions.

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The theory: The moon's gravitational pull affects ocean tides, which made scientists wonder if it could mess with the fluid in our bodies and possibly disrupt circulation and heart rate. After all, we are 60 percent water.

The truth: Nope, says research on the subject. The gravitational pull of the moon is negligible on the human body (it's far away, and we're really small). The true ticker troublemakers: high blood pressure, high cholesterol, and obesity.

The theory: Nearly two-thirds of emergency M.D.s said they're busier when the moon's out, per a 2009 survey. People in biblical times made the connection too, believing that a full moon could cause temporary lunacy—i.e., bouts of insanity linked to the lunar cycle. It's not a great mental leap to assume those erratic behaviors could cause traffic or other accidents.

The truth: While more dogs and cats land in the ER in the days around a full moon (possibly because pets are more active when it's brighter out), not so with humans. A 2011 study found that the glow (along with zodiac signs and Friday the 13th) has no effect on ER visits. Why docs thought otherwise? Some experts blame our tendency to impose order on a random universe by seeing patterns where they don't exist.

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The theory: Anthropologists speculate that our primitive ancestors may have been awake under the glow of the moon (but likely to watch for predators). And previous research seemed to point to a change in circadian rhythm that might make you lose more Zs.

The truth: The real reason your body clock is out of whack, according to the most recent science, is bad sleep hygiene—scrolling Instagram in bed, knocking back a latte at 4 p.m., stress, or an irregular schedule.

The theory: Folklore all the way back to ancient Rome suggests the full moon made people cranky, aggressive, anxious, and more prone to criminal behavior. (One theory attributes this to sleep deprivation, but we already busted that one.)

The truth: Approximately 100 studies have attempted to link emotional states to the moon; the vast majority found no correlation whatsoever. Our assessment: Perhaps scientific funding is better spent elsewhere—like, you know, trying to find cures for diseases.