"It's a full moon, that explains it" is one of those phrases that gets said in hospitals, schools, and group chats alike. The belief that lunar phases affect human behavior — the so-called "lunar effect" — is one of the oldest and most persistent pieces of folklore we have.
Where the belief comes from
The word "lunatic" itself comes from "luna," reflecting centuries-old beliefs linking moonlight to madness. Before electric lighting, a full moon meant genuinely brighter nights, which plausibly did disrupt sleep and change nighttime behavior — a real effect with a mundane cause, later folded into more mystical explanations.
What does modern research actually find?
Large-scale studies looking at hospital admissions, crime rates, and sleep quality across lunar cycles have generally found no consistent statistical link to the moon's phase. A few individual studies have reported small effects on sleep (people falling asleep slightly later and sleeping slightly less around the full moon), but the effect size is small and hasn't replicated reliably across all research. The honest scientific summary is: mostly no effect, with a possible minor exception for sleep that's still debated.
So why does the belief persist?
Partly folklore, partly confirmation bias — we're more likely to notice and remember a rough night's sleep when we can blame it on something (like a supermoon) than when we chalk it up to ordinary randomness. The moon also has genuine, undisputed physical effects — tides — which makes it easy to intuitively extend "the moon moves oceans" to "the moon moves us," even though our bodies aren't tidal systems.
Using moon phases as a ritual, not a rulebook
Even without a scientific mechanism, many people find value in using the lunar cycle as a rhythm for reflection: new moon for setting intentions, full moon for reviewing and releasing. Used this way, it functions less like astrology and more like a recurring calendar reminder with a bit of poetry attached — which is a perfectly good reason to enjoy it.