5 Fears and Myths About the Full Moon

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It seems almost everyone, from love-struck couples to poets and filmmakers, adores a full Moon. Many people through the years have tried to link the passage of the full Moon to everything from earthquakes to a rise in suicide and crime rates and more. Some of these myths date back to ancient man, but others were spawned on the Internet, where they can be counted on to circulate forever. Here are just a few strange beliefs and ideas mistakenly linked to our nearest neighbor in space.


5. Fear of the Full Moon Dates to Ancient Times

Moonrise over the Organ Mountains near Las Cruces, New Mexico. © James Hill

Moonrise over the Organ Mountains near Las Cruces, New Mexico. © James Hill

The added illumination of a full Moon at dusk was beneficial to early man, extending the hours for hunt and harvest. Despite this, many felt that no good occurred under the light of a full Moon. In fact, the Roman name for the goddess of the Moon, Luna, still turns up in modern-day use through the words “lunacy” and “lunatic.” Folklore says a woman can become pregnant sleeping in the light of the full Moon (a convenient story, for sure), and of course we have tales of men turning into werewolves under the light of a full Moon. In fact, selenophobia describes a fear of the Moon, and one could easily imagine this anxiety might become acute to a sufferer near full phase. An ancient fear of the number 13 is also based in part on the Moon, as most years only contain 12 full Moons, with an occasional 13th being considered unlucky. Likewise, the second full Moon in the occasional month containing two — which isn’t all that rare, as it occurs every few years — has become known as a “Blue Moon.”


4. The Moon Affects the Oceans … So It Must Affect Humans, Right?

The full Moon shines over bungalows in French Polynesia. © VGM 8383

The full Moon shines over bungalows in French Polynesia. © VGM 8383

The daily passage of the Moon and to a lesser extent, the Sun, powers tides worldwide. So shouldn’t that movement have an influence on the human body, which is roughly two-thirds water? It sounds as if it must be true, but it’s not. The Earth’s oceans are massive, and this twice-daily gravitational surge is acting over large scales: even over the size of smaller bodies of water such as the Great Lakes, this tidal effect is measured in mere inches. Scale that down even further to human size and the effect is minuscule. Plus, high spring tides also occur near the new Moon as well as full Moon, to much less fanfare. It’s been duly noted that a baby held in a woman’s arms is exerting far more gravitational influence on her body than is the Moon. Still, theories persist that, for example, the Moon’s gravitational influence on the water in our brains causes more mental-health issues under a full Moon.


3. Some Studies Allege Links Between the Full Moon and Human Behavior

The Golden Gate Bridge support cables frame a rising full Moon. © Pargon

The Golden Gate Bridge support cables frame a rising Moon. © Pargon

You’ll find a few believers for this theory in every occupation that has a night shift. Anecdotal evidence suggests more babies are born under the full Moon. There are claims that emergency room visits and crime rates increase. Every so often, a study emerges claiming that the full Moon has an effect on mental health-related incidents, or there are more car accidents. Other scholars immediately begin poking holes in the methodology. When you analyze these claims statistically and over large datasets, the effects vanish. In the case of births, the effect should be readily apparent if births were clustered in sync with the lunar cycle. Keep in mind, the technical point when the Moon becomes “full” is an instant— the point it reaches its closest to 180 degrees opposite to the Sun. The Moon’s orbit is tilted 5 degrees relative to the Earth’s, so when it does fall exactly opposite to the Sun, a total lunar eclipse occurs… the Moon never reaches full 100% illumination from our Earthly vantage point!

The idea of linking the night of a full Moon to an event is a version of the Gambler’s Fallacy, a misconception of correlation versus causation where we tend to count the hits and disregard the misses. Emergency room workers expecting a bad night under the full Moon will be more likely to focus on such nights that are bad, and forget those nights that are quiet.


2. Does the Full Moon Cause Earthquakes?

Contrary to popular belief, the full Moon does not cause earthquakes. © John via Flickr

Contrary to what some believe, the full Moon does not cause earthquakes. © John via Flickr

This is another idea that arises with every supermoon; it seems plausible, but vanishes under scrutiny. The Moon does raise “land tides,” though they’re tiny in comparison to those seen in our much more malleable liquid oceans. Many will point to earthquakes such as the 2011 event in Christchurch, New Zealand, which occurred a few days before a full Moon, although many large earthquakes occur every year, and it’s not hard to find a few that happened near a full Moon. One would-be earthquake prophet even predicted that the next major earthquake would occur within a week of the full or new Moon, a pretty safe bet as the specified timetable works out to 28 days, just a day and half less than the synodic lunar cycle that the Moon spans to return to the same phase. Although one 2003 Taiwanese study claimed a weak correlation between full Moons and earthquakes, the USGS has gone on record as stating no proven link exists.


1. Proving the Full Moon Has No Negative Effects Is Impossible

A crowd checks out the Grand Canyon under the full Moon. © Geoff Livingston

A crowd checks out the Grand Canyon under the full Moon. © Geoff Livingston

Why do some people still fear that the full Moon creates spikes in accidents, heart attacks, crime, etc.? Because there is no way to disprove these theories. While it’s true that we can’t currently prove that the full Moon has no effect on humans (in science, this is known as disproving the null hypothesis), such a result would, at least, keep researchers from wasting their time. Although such credulous studies make their rounds near every supermoon, they’re beginning to sound as phony as claims by Moon-landing deniers that we never went to the Moon, or for that matter, that it’s actually made of green cheese.

One final example of a full Moon fallacy is the idea that the human menstrual cycle is linked to the full Moon. In fact, the term “menses” comes from the Latin word for “month,” and is tied to the notion that ovulation and menstruation is linked to the new and full Moon. A rigorous meta-analysis conducted in 1996 found no link, and the average menstruation span actually covers a fairly wide range from 22 to 35 days, which can be open to much wider interpretation. Although it’s interesting to consider how and why this cycle evolved, we must look to something other than the Moon for its source.


Written by

David Dickinson is a backyard astronomer, science educator and retired military veteran. He lives in Hudson, Fla., with his wife, Myscha, and their dog, Maggie. He blogs about astronomy, science and science fiction at www.astroguyz.com.