Lunar effect

Based on Wikipedia: Lunar effect

The Moon in Our Minds

In 2007, police officers in Brighton, England, announced they would deploy extra staff during full moons to handle the surge in violent crime they believed was coming. A spokeswoman told reporters their research showed "a correlation between violent incidents and full moons." That same year, police in Ohio and Kentucky blamed crime spikes on lunar cycles. A year later, New Zealand's Justice Minister suggested that a rash of stabbings might have been caused by the moon.

None of them were right.

The belief that the moon influences human behavior is ancient, persistent, and almost entirely unsupported by evidence. The very word "lunatic" derives from Luna, the Roman goddess of the moon, encoding the assumption that madness waxes and wanes with the lunar cycle. Hospital workers, police officers, teachers, and bartenders routinely claim that full moons bring out the worst in people. It feels true. It seems obviously true.

But when scientists actually count the incidents—the births, the crimes, the emergency room visits, the psychiatric episodes—the moon's supposed influence vanishes like mist.

The Science of Disbelief

By the late 1980s, researchers had published at least forty studies examining the supposed connection between lunar cycles and mental disturbances, plus another twenty looking at whether more babies are born during full moons. The results were strikingly consistent: no correlation whatsoever.

Consider the birth studies alone. In 1957, researchers analyzed 9,551 births in a Pennsylvania hospital and found no lunar pattern. A four-year study of nearly 12,000 births at the University of California, Los Angeles medical center—including a subset of 8,142 natural births unaffected by drugs or cesarean sections—showed the same thing: nothing. Phoenix, Arizona: 168,000 spontaneous vaginal deliveries between 1995 and 2000. No relationship. North Carolina: 564,000 births over four years. No predictable influence. Hannover, Germany: 6,725 deliveries over six years. Nothing.

Then came the definitive study: 70 million American birth records from the National Center for Health Statistics.

No correlation with the moon.

An extensive review of 21 studies from seven different countries found that the majority showed no relationship, and the few positive results contradicted each other. The moon, it seems, has nothing to do with when babies arrive.

Except—and this is where science gets interesting—a 2021 French study found something. Analyzing 38.7 million births over fifty years, with careful statistical controls for holidays and other confounding factors, researchers detected a tiny surplus of births on full moon days: exactly 0.4 percent more than average.

That finding was statistically significant, with only about a one-in-100,000 chance of being random noise. But here's the crucial point: a 0.4 percent increase is completely impossible to detect by observation. No nurse, no midwife, no obstetrician working in a maternity ward could ever notice such a minuscule difference, even over an entire career. The widespread belief that full moons pack labor and delivery units with extra patients simply isn't true. The effect, if it exists at all, is invisible to everyone except statisticians with access to national databases.

Blood, Crime, and Other Myths

What about surgery? There's an old claim that surgeons used to refuse to operate during full moons because patients bled more profusely. In 2009, a British politician named David Tredinnick stated publicly that "surgeons will not operate because blood clotting is not effective" during full moons. A spokesman for the Royal College of Surgeons responded that his colleagues would "laugh their heads off" at the suggestion.

One research team in Barcelona did report a weak correlation between lunar phases and hospital admissions for gastrointestinal bleeding. But their methodology drew criticism: they compared full moon days to all non-full moon days lumped together. When other researchers compared the full moon to specific other days in the lunar cycle—day 9, day 12, day 13, day 27—the statistical significance disappeared entirely. Some of those other days actually had nearly identical admission rates.

Crime statistics tell a similar story. A study of more than 23,000 aggravated assaults in Germany between 1999 and 2005 found no correlation with lunar phases. That famous Miami-Dade County study claiming to find a link between moon phases and homicides? Later analysis revealed the original researchers had used "inappropriate and misleading statistical procedures." The data didn't support their conclusions.

One 2016 study did find that outdoor crime in Washington, D.C., increased slightly on brighter moonlit nights—but indoor crime didn't change at all. The researchers speculated that criminals could simply see better when the moon was bright, making it easier to assess potential victims and spot unsecured property. More people might also be out walking on pleasant, well-lit evenings. This isn't a mystical lunar influence; it's just better lighting.

Sleep: A Complicated Picture

The sleep research is messier and more intriguing. In 2013, Christian Cajochen and his colleagues at the University of Basel in Switzerland reported that people slept worse around the full moon. But the study had only 33 participants and didn't properly control for age and sex differences. A larger 2014 study with better experimental controls found no effect.

Then things got strange. A 2015 study of 795 children found they slept three minutes longer near the full moon. A 2016 study of 5,812 children found they slept five minutes less. Neither difference is meaningful in practical terms, and the lead scientist concluded: "Our study provides compelling evidence that the moon does not seem to influence people's behavior."

But a 2021 study from researchers at the University of Washington, Yale, and Argentina's National University of Quilmes found something more substantial. In the days before a full moon, people went to bed later and slept for shorter periods—in some cases up to 90 minutes less. This happened even in locations with full access to electric lighting, suggesting the effect wasn't simply about moonlight streaming through windows.

A Swedish study added another wrinkle: men whose sleep was recorded during the waxing moon (the phase when the visible portion grows larger night by night) showed lower sleep efficiency and spent more time awake after initially falling asleep, compared to men recorded during the waning moon. Women's sleep, interestingly, showed no such pattern.

What should we make of these contradictory findings? Science is a process, not a verdict. The most honest answer is that if the moon affects human sleep at all, the effect is small, variable, and far from settled.

A Cultural Fossil

If the moon doesn't actually influence human behavior in any meaningful way, why do so many people believe it does?

A 1999 study offered a fascinating hypothesis: the lunar-lunacy connection might be a "cultural fossil" from before the invention of artificial lighting. Before gas lamps and electric bulbs, the full moon was the brightest light in the night sky—bright enough to disrupt sleep for anyone living outdoors or in poorly sealed dwellings. Sleep deprivation can trigger erratic behavior in people predisposed to conditions like bipolar disorder. In those pre-modern conditions, the full moon might genuinely have caused visible behavioral changes in some individuals.

That effect would have been real, but it had nothing to do with mystical lunar influence. It was simply about light and sleeplessness. Once humans moved indoors and invented window shades, the effect disappeared—but the belief persisted.

Psychologists point to another explanation: illusory correlation, the human tendency to perceive connections that don't actually exist. When something unusual happens during a full moon, we notice and remember it. When something unusual happens on an ordinary night, we don't give the moon a second thought. Over time, this selective attention creates a powerful false memory of lunar influence. The belief confirms itself.

Where the Moon Actually Matters

Here's the twist in this story: while the moon has little measurable effect on humans, it profoundly influences other species. The lunar cycle is not imaginary—it's a 29.5-day astronomical reality that shapes ocean tides and patterns of nighttime illumination. Many animals have evolved to synchronize their behavior with this cycle, and the mechanisms are genuinely remarkable.

Corals, for instance, contain proteins called cryptochromes that are sensitive to different levels of light. Species like Dipsastraea speciosa coordinate their spawning to occur in the evening or night around the last quarter moon. The trigger appears to be a period of darkness between sunset and moonrise. The Great Barrier Reef's famous mass spawning events—when billions of eggs and sperm release simultaneously—always happen after the full moon between October and December.

The bristle worm Platynereis dumerilii has become a model organism for studying these biological mechanisms. It spawns a few days after each full moon, and researchers have identified a protein called L-Cry that can actually distinguish between sunlight and moonlight. The protein contains two strands with light-absorbing structures called flavins, and these respond differently to solar versus lunar illumination. Another molecule, r-Opsin, may function as a moonrise sensor. Scientists are still working out exactly how these molecular signals translate into synchronized reproductive behavior.

California grunion fish offer one of nature's most spectacular examples of lunar timing. During spring and summer, these small silver fish perform an unusual mating ritual on beaches. The females ride incoming waves onto the sand, dig themselves tail-first into the beach, lay their eggs, and are then fertilized by males who wrap around them. The egg-laying takes place on four consecutive nights beginning with the full and new moons—precisely when tides are highest. The highest tides occur when the Sun, Earth, and Moon align, which happens twice per lunar month.

This isn't mysticism. It's physics. The gravitational pull of the Moon (with a modest assist from the Sun) creates ocean tides. Animals that live in tidal zones have evolved to anticipate these predictable changes. Fiddler crabs stay in their burrows during high tide and emerge to feed when the water recedes. They release their fertilized eggs into the outgoing tide. The marine iguanas of the Galápagos Islands time their trips to the sea to arrive at low tide, when feeding is easiest.

Even insects show lunar effects. The body weight of honeybees peaks during the new moon. A tiny midge called Clunio marinus has a biological clock synchronized with lunar cycles. Many moth species use moonlight to navigate, maintaining stable flight paths by keeping the moon at a constant angle—a strategy that famously fails when they encounter artificial lights, which they spiral toward as if trying to navigate by a suddenly nearby moon.

The Human Menstrual Cycle: A Red Herring

One of the most persistent lunar myths involves the human menstrual cycle, which averages about 28 days—remarkably close to the 29.5-day lunar month. This coincidence has led many people to assume a biological connection, perhaps rooted in our evolutionary past.

The evidence suggests the similarity is exactly that: a coincidence. No study has conclusively demonstrated that menstrual cycles synchronize with lunar phases. And the 28-day average is just that—an average. Individual cycles vary considerably, ranging from about 21 to 35 days in healthy women. If menstruation were truly tied to the moon, we'd expect much tighter clustering around the lunar month.

More tellingly, other mammals don't share this pattern. Chimpanzees have 36-day cycles. Dogs go into heat roughly twice a year. Cats cycle every two to three weeks during breeding season. The human menstrual length appears to be the result of our particular evolutionary history, not a response to lunar influence.

What We See When We Look Up

The story of the lunar effect is really two stories. One is about the natural world, where the moon's gravitational and illuminating influences have shaped the evolution of countless species, from coral to grunion to bristle worms. These effects are measurable, mechanistically understood, and genuinely fascinating.

The other story is about human psychology—about our remarkable ability to perceive patterns that aren't there, to remember the unusual and forget the ordinary, to hold onto beliefs that feel true even when the evidence points elsewhere. Police officers in Brighton really did believe their crime rates rose during full moons. They weren't lying; they were just human, subject to the same cognitive biases as everyone else.

A meta-analysis of 37 studies examining relationships between lunar phases and human behavior found no significant correlation. Nearly half of the 23 studies that had claimed to show some effect contained at least one statistical error. Reviews of studies on lunar phases and suicide reached similar conclusions: most found nothing, and those that reported positive results contradicted each other.

The moon is beautiful. It has genuine physical effects on our planet—it drives the tides, stabilizes Earth's axial tilt, and lights the night with reflected sunlight. For billions of years, its rhythms have shaped the evolution of life in the oceans.

But it does not make us crazy. It does not make more babies arrive. It does not thin our blood or thicken the ranks of criminals in the streets.

The lunar effect on humans exists primarily in one place: our minds, where we construct meaning from coincidence and remember the nights when the full moon rose and something strange happened. Those memories are real. The connection is not.