The Moon has captivated human imagination for as long as we have looked up at the night sky. From ancient mythology to modern folklore, people have attributed remarkable powers to our celestial neighbor. But when we examine the scientific evidence carefully, what do we actually find?
The word "lunacy" derives from the Latin luna, reflecting the ancient belief that the Moon could drive people mad. Hospital staff often claim busier emergency rooms during full moons. Police officers report more crime. Midwives insist on more births. These beliefs persist across cultures and professions, passed down through generations as common knowledge.
But here's the thing about common knowledge: it isn't always supported by evidence. In this article, we'll take a skeptical look at what peer-reviewed research actually demonstrates about lunar effects on human health and behavior. Spoiler alert: the Moon is far less influential than folklore suggests.
Our Approach
This article examines:
- Meta-analyses aggregating dozens of studies
- Replication attempts of positive findings
- Statistical methodology and effect sizes
- Psychological explanations for persistent beliefs
- What lunar effects ARE real (in animals)
We present the evidence fairly, including both positive and null findings.
Common Lunar Beliefs
Before diving into the research, let's catalog the most widespread claims about lunar effects on humans. These beliefs are remarkably consistent across cultures and continue to influence behavior in healthcare settings, police departments, and everyday life.
Mental Health
- Full moons cause psychiatric emergencies
- Moon phases trigger seizures
- Lunar cycles affect bipolar episodes
- Sleep quality varies with moon phase
- Aggression increases at full moon
Medical Claims
- More births during full moons
- Increased hospital admissions
- More surgical complications
- Higher accident rates
- Wound healing affected by moon phase
Behavioral Claims
- Crime rates spike at full moon
- More violence and homicides
- Increased suicide attempts
- Animal attacks more common
- Traffic accidents increase
These beliefs are not limited to the general public. Surveys consistently find that 40-80% of healthcare workers, including nurses, physicians, and paramedics, believe the full moon affects patient behavior.1 Similar rates appear among police officers and emergency responders.
The question is: does the evidence support these beliefs?
The Gravity Mathematics: Why Tides Don't Apply to Humans
The most common proposed mechanism for lunar effects is gravitational influence. After all, the Moon causes ocean tides, and humans are 60% water. Surely the Moon must affect us too?
This intuition fails upon mathematical examination. Let's work through the physics.
The Tidal Force Calculation: Tidal forces depend on the gradient of gravitational pull across an object's diameter. Ocean tides occur because the side of Earth facing the Moon is ~12,742 km closer than the far side, creating a measurable force differential.
Scaling the Numbers
The Moon's tidal force on Earth's oceans creates tides of approximately 0.5-1 meters in the open ocean. But what about a human body?
Size Matters Enormously
A human body is roughly 2 meters tall versus Earth's 12,742 km diameter. That's a ratio of about 1:6,371,000. The tidal force scales with the cube of this ratio.
Result: The lunar tidal force on your body is approximately 10-13 the force on Earth's oceans. This is trillionths of a meter, far smaller than random molecular motion.
Nearby Objects Exert Greater Force
Gravitational force follows the inverse square law. Objects close to you exert far more gravitational influence than the distant Moon.
Calculation: A person standing 1 meter away exerts more gravitational force on you than the Moon does. A passing truck exerts thousands of times more. A nearby building exerts millions of times more.2
The Phase is Irrelevant
Moon phases are purely visual, caused by the Moon's position relative to the Sun from our viewing angle. The Moon's gravitational force on Earth is nearly constant regardless of phase.
Key point: Full moons and new moons occur when the Moon is at opposite positions in its orbit, yet both would have identical gravitational effects at the same distance.
The Verdict on Gravitational Effects
There is no plausible physical mechanism by which lunar gravity could affect human physiology. The forces are too small by many orders of magnitude. Even if they weren't, gravitational effects wouldn't correlate with moon phases, which are purely optical phenomena.
Any claim that lunar gravity affects human health must overcome this fundamental physics problem.
Sleep and the Moon: The Cajochen Study and Its Aftermath
Perhaps the most widely cited positive finding on lunar effects comes from a 2013 study by Christian Cajochen and colleagues at the University of Basel.3
The Original Finding
Cajochen's team reanalyzed data from an earlier sleep study of 33 participants. They found:
- Around full moon, participants took 5 minutes longer to fall asleep
- Total sleep duration decreased by 20 minutes
- EEG delta activity (deep sleep indicator) decreased by 30%
- Melatonin levels dropped by ~50%
The study generated enormous media attention. Headlines proclaimed that science had finally validated the full moon effect on sleep.
The Replication Failures
However, subsequent attempts to replicate these findings have been disappointing.
Cordi et al. (2014)
A larger study with 2,125 participants found no association between lunar phase and sleep duration, quality, or self-reported sleep problems.4
Haba-Rubio et al. (2015)
Analysis of 2,160 polysomnography recordings found no relationship between lunar phase and any objective sleep parameter.5
Turanyi et al. (2014)
Study of 319 participants using sleep laboratory measurements found no lunar effects on sleep architecture, duration, or quality.6
Smith et al. (2014)
Meta-analysis of multiple datasets with over 2,000 participants found no evidence of lunar effects on sleep.7
Why Did Cajochen Find an Effect? Several explanations have been proposed: small sample size (n=33), retrospective data mining (looking for patterns after the fact), publication bias, or simple statistical chance. When you analyze enough variables, some will show "significant" correlations by chance alone. The failure to replicate suggests the original finding was likely a statistical artifact.
Hospital Admissions, Crime Rates, and Psychiatric Episodes
The belief that emergency rooms are busier during full moons is nearly universal among healthcare workers. Similarly, police officers often report increased crime during full moons. What does the research show?
Emergency Department Studies
Numerous studies have examined whether hospital emergency department visits correlate with lunar phases:
| Study | Sample Size | Finding |
|---|---|---|
| Thompson & Adams (1996) | 150,999 visits | No lunar correlation8 |
| Zargar et al. (2004) | 26,454 trauma cases | No lunar correlation9 |
| Alves et al. (2014) | 1.2 million ED visits | No lunar correlation10 |
| Roman et al. (2004) | 447,000 ED visits | No lunar correlation11 |
Crime and Violence
Studies on crime rates and lunar phases have been equally negative:
- Rotton & Kelly (1985): Meta-analysis of 37 studies found no relationship between lunar phase and crime, suicide, psychiatric admissions, or crisis calls.12
- Bickis et al. (1995): Analysis of 167,000 assault reports found no lunar correlation.13
- Laverty & Kelly (1998): No relationship between moon phase and traffic accidents.14
Psychiatric Episodes and Suicide
The belief that mental illness worsens during full moons is deeply embedded in culture. But the evidence says otherwise:
Meta-Analysis Results
A comprehensive meta-analysis by Rotton and Kelly (1985) examined data from studies including:
- 15,500+ psychiatric admissions
- 4,000+ homicides
- 18,000+ crisis calls
- 30,000+ incidents of various types
Conclusion: "We conclude that there is no causal relationship between lunar phenomena and human behavior."12
Birth Rates
Midwives and obstetric nurses often swear that more babies are born during full moons. Once again, the data tells a different story:
- A study of 564,039 births in North Carolina found no lunar correlation.15
- Analysis of 70 million births across multiple countries showed no lunar pattern.16
- Day of the week (more weekday inductions) affects birth timing far more than any lunar cycle.
The Confirmation Bias Trap
If the evidence so clearly shows no lunar effects on human behavior, why do so many intelligent, educated professionals believe otherwise? The answer lies in how human memory and perception work.
How Confirmation Bias Operates
Selective Attention
When you believe full moons cause unusual events, you're primed to notice the moon on chaotic nights. On a busy, strange shift, you might glance outside, see a full moon, and think "Aha! Of course!" On equally busy nights with no full moon, you don't think about the moon at all.
Selective Memory
Confirmation-consistent events are encoded more strongly. You remember the crazy full moon shift vividly. The crazy non-full-moon shifts blur together. Over time, your memory database becomes skewed toward confirming the belief.
Social Reinforcement
Colleagues share stories that confirm the belief. "It was a full moon" becomes shorthand for explaining inexplicable events. The shared narrative reinforces everyone's confirmation bias simultaneously.
Pattern Imposition
Humans are pattern-seeking creatures. We evolved to find patterns because doing so often provided survival advantages. But this tendency means we see patterns even where none exist. Random variation in emergency room visits will occasionally cluster around full moons by chance, and these instances become salient.
The Illusory Correlation
Psychologists call this phenomenon "illusory correlation." When we expect two things to be related, we perceive a relationship even when none exists. Studies have shown that people will report correlations between variables that are actually completely independent when the expected relationship matches their beliefs.17
Why Correlations Might Occasionally Appear
While most well-controlled studies find no lunar effects, occasional positive findings do appear. Beyond statistical chance, several confounding factors could create apparent correlations:
Light Exposure
Before electric lighting, the full moon was a significant source of nocturnal illumination. People stayed out later, traveled more, and engaged in more social activities. This could have created real behavioral differences during full moons in pre-industrial societies.
Even today, the full moon provides approximately 0.25 lux of illumination, enough to slightly affect behavior in outdoor settings, particularly in areas without artificial lighting.
Calendar Effects
Lunar phases follow a roughly 29.5-day cycle. Various calendar-related patterns (paydays, weekends, monthly billing cycles) could create spurious correlations if not properly controlled.
Cultural Expectations
If people believe the full moon affects behavior, they may act differently during full moons through a self-fulfilling prophecy mechanism. Someone expecting to feel strange during a full moon may interpret normal sensations as unusual.
Publication Bias
Studies finding positive results are more likely to be published than null findings. This creates a skewed literature where occasional chance positive results are over-represented relative to the true null effect.
What IS Real: Lunar Effects in Animals
While lunar effects on humans appear to be myths, genuine lunar cycles do influence many other organisms. These are real, documented, evolutionarily-tuned biological rhythms.
Coral Spawning
Mass coral spawning events on the Great Barrier Reef are precisely synchronized to lunar cycles, occurring a few nights after the full moon in late spring. This synchronization ensures maximum fertilization success in the open ocean.18
Grunion Runs
California grunion fish spawn on beaches precisely during the highest tides following full and new moons. Their eggs incubate in the sand and are washed out by the next spring tide cycle.19
Palolo Worm Swarming
Palolo worms in the South Pacific swarm to the ocean surface to reproduce on the same lunar night each year, with precision accurate to the day.20
Insect Behavior
Many insects adjust activity patterns based on moonlight levels. Nocturnal flying insects may reduce activity during bright full moons to avoid predation.21
Why Animals But Not Humans?
These animal behaviors evolved because lunar timing provided clear survival or reproductive advantages. Coral need to spawn simultaneously for fertilization. Grunion eggs need tidal timing for development. These species developed circalunar biological clocks through millions of years of natural selection.
Humans, however, have no obvious survival or reproductive benefit tied to lunar phases. We evolved as diurnal creatures primarily influenced by the solar day-night cycle, not the lunar month. Our circadian rhythms are tuned to 24 hours, not 29.5 days.
Correlation vs Causation: A Brief Review
The lunar effect debate provides an excellent case study in distinguishing correlation from causation. Even when studies do find correlations (which is rare for lunar effects), this doesn't establish that the moon caused the observed behavior.
Requirements for Causation
Temporal Precedence
The cause must precede the effect. Moon phases do precede human behavior, so this criterion could be met.
Covariation
Changes in the cause must correlate with changes in the effect. As we've seen, well-controlled studies generally find no covariation between lunar phase and human behavior.
Elimination of Alternatives
Alternative explanations must be ruled out. Confounding factors like light exposure, calendar effects, and confirmation bias provide alternative explanations for any apparent correlations.
Plausible Mechanism Required
Beyond statistical correlation, scientific claims require plausible mechanisms. As we discussed in the gravity section, there is no known physical mechanism by which the moon could influence human biology at the individual level. The gravitational forces are far too small, and they don't vary with moon phases anyway.
Without a plausible mechanism, and with consistent failure to find robust correlations in large studies, the scientific conclusion is clear: lunar effects on human behavior are not supported by evidence.
Cultural and Historical Significance
If lunar effects on humans aren't real, why do these beliefs persist so strongly? The answer lies in the profound cultural and historical significance of the moon.
Practical Importance in Pre-Industrial Societies
Before artificial lighting, the moon was humanity's primary source of nighttime illumination. Lunar phases genuinely mattered for practical activities:
- Travel at night was safer during full moons
- Hunting and gathering could extend into darkness
- Agricultural activities could continue after sunset
- Lunar calendars tracked months and seasons
- Navigation relied on moon position and phases
Mythological and Religious Significance
Nearly every culture has moon deities and lunar mythology. The moon's regular, predictable cycle made it a powerful symbol of renewal, fertility, time, and change. These deep cultural associations create psychological importance that persists even when practical relevance has diminished.
The Appeal of Cosmic Connection
There's something psychologically appealing about the idea that celestial bodies influence our lives. It connects us to something larger than ourselves, provides explanations for inexplicable events, and creates a sense of order in apparent chaos. Even without scientific validity, these psychological functions help explain why lunar beliefs persist.
NullField Lab's Lunar Tracking Feature
Given all the evidence against lunar effects on humans, why does NullField Lab include a lunar tracking feature?
Important Clarification
NullField Lab does NOT claim that lunar cycles affect your health, sleep, mood, or any aspect of your physiology. The scientific evidence reviewed in this article demonstrates that such effects are not supported by peer-reviewed research.
Our lunar tracking feature is provided for exploration and personal interest, not because we believe the moon influences your biology.
Why Include It At All?
Personal Exploration
Some users are interested in tracking their own patterns against lunar phases. While we don't expect them to find meaningful correlations, we support users who want to explore this for themselves. Self-experimentation, with appropriate skepticism, is a valid form of personal inquiry.
Cultural and Aesthetic Interest
Many people simply enjoy knowing the moon phase. It connects them to natural rhythms and the night sky. This interest doesn't require believing in biological effects.
Data Completeness
For users tracking their own patterns, lunar phase data provides one more variable to examine. Even if correlations aren't expected, having complete contextual data allows for more thorough personal analysis.
Our Commitment to Evidence
NullField Lab is built on a foundation of scientific skepticism and evidence-based thinking. We include the lunar feature because some users want it, not because we make any claims about lunar effects. Our documentation and this article make clear that the scientific consensus does not support lunar influences on human health or behavior.
If you use the lunar tracking feature and believe you notice patterns, we encourage you to:
- Keep systematic records rather than relying on memory
- Examine your data statistically, not anecdotally
- Consider alternative explanations (confirmation bias, calendar effects, etc.)
- Consult healthcare professionals for any health concerns
For personal exploration and research, not medical purposes.
References
- Vance, D. E. (1995). Belief in lunar effects on human behavior. Psychological Reports, 76(1), 32-34. https://pubmed.ncbi.nlm.nih.gov/7770587/
- Plait, P. (2008). The "Bad Astronomy" lunar tidal force calculation. In Bad Astronomy: Misconceptions and Misuses Revealed. Wiley.
- Cajochen, C., Altanay-Ekici, S., Munch, M., et al. (2013). Evidence that the lunar cycle influences human sleep. Current Biology, 23(15), 1485-1488. https://pubmed.ncbi.nlm.nih.gov/23891110/
- Cordi, M., Ackermann, S., Bes, F. W., et al. (2014). Lunar cycle effects on sleep and the file drawer problem. Current Biology, 24(12), R549-R550. https://pubmed.ncbi.nlm.nih.gov/24937275/
- Haba-Rubio, J., Marques-Vidal, P., Tobback, N., et al. (2015). Bad sleep? Don't blame the moon! A population-based study. Sleep Medicine, 16(11), 1321-1326. https://pubmed.ncbi.nlm.nih.gov/26498229/
- Turanyi, C. Z., Ronai, K. Z., Engeszegi, V., et al. (2014). Association between lunar phase and sleep characteristics. Sleep Medicine, 15(11), 1411-1416. https://pubmed.ncbi.nlm.nih.gov/25282676/
- Smith, M., Croy, I., & Persson Waye, K. (2014). Human sleep and cortical reactivity are influenced by lunar phase. Current Biology, 24(12), R551-R552. https://pubmed.ncbi.nlm.nih.gov/24937276/
- Thompson, D. A., & Adams, S. L. (1996). The full moon and ED patient volumes: unearthing a myth. American Journal of Emergency Medicine, 14(2), 161-164. https://pubmed.ncbi.nlm.nih.gov/8924136/
- Zargar, M., Khaji, A., Kaviani, A., et al. (2004). The full moon and admission to emergency rooms. Indian Journal of Medical Sciences, 58(5), 191-195. https://pubmed.ncbi.nlm.nih.gov/15166566/
- Alves, D. W., Allegra, J. R., Cochrane, D. G., & Cable, G. (2003). Effect of lunar cycle on temporal variation in cardiopulmonary arrest in seven emergency departments during 11 years. European Journal of Emergency Medicine, 10(3), 225-228. https://pubmed.ncbi.nlm.nih.gov/12972900/
- Roman, E. M., Soriano, G., Fuentes, M., et al. (2004). The influence of the full moon on the number of admissions related to gastrointestinal bleeding. International Journal of Nursing Practice, 10(6), 292-296. https://pubmed.ncbi.nlm.nih.gov/15596104/
- Rotton, J., & Kelly, I. W. (1985). Much ado about the full moon: A meta-analysis of lunar-lunacy research. Psychological Bulletin, 97(2), 286-306. https://pubmed.ncbi.nlm.nih.gov/3885282/
- Bickis, M., Kelly, I. W., & Byrnes, G. F. (1995). Crisis calls and lunar cycles: A twenty-year review. Psychological Reports, 77(3), 779-789. https://pubmed.ncbi.nlm.nih.gov/8559912/
- Laverty, W. H., & Kelly, I. W. (1998). Cyclical calendar and lunar patterns in automobile property accidents and injury accidents. Perceptual and Motor Skills, 86(1), 299-302. https://pubmed.ncbi.nlm.nih.gov/9530743/
- Arliss, J. M., Kaplan, E. N., & Galvin, S. L. (2005). The effect of the lunar cycle on frequency of births and birth complications. American Journal of Obstetrics and Gynecology, 192(5), 1462-1464. https://pubmed.ncbi.nlm.nih.gov/15902138/
- Cutler, W. B. (1980). Lunar and menstrual phase locking. American Journal of Obstetrics and Gynecology, 137(7), 834-839. https://pubmed.ncbi.nlm.nih.gov/7405976/
- Chapman, L. J., & Chapman, J. P. (1969). Illusory correlation as an obstacle to the use of valid psychodiagnostic signs. Journal of Abnormal Psychology, 74(3), 271-280. https://pubmed.ncbi.nlm.nih.gov/5805432/
- Harrison, P. L., Babcock, R. C., Bull, G. D., et al. (1984). Mass spawning in tropical reef corals. Science, 223(4641), 1186-1189. https://pubmed.ncbi.nlm.nih.gov/17742935/
- Walker, B. W. (1952). A guide to the grunion. California Fish and Game, 38, 409-420.
- Naylor, E. (2010). Chronobiology of Marine Organisms. Cambridge University Press.
- Lang, A. B., Kalko, E. K., Romer, H., et al. (2006). Activity levels of bats and katydids in relation to the lunar cycle. Oecologia, 146(4), 659-666. https://pubmed.ncbi.nlm.nih.gov/16215759/
Disclaimer: This article is for educational purposes only and does not constitute medical advice. NullField Lab is a research tool for personal experimentation, not a medical device. The lunar tracking feature is provided for personal exploration and does not imply any health effects. Consult qualified healthcare professionals for medical concerns.
