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15 Crazy Moon Fallacies

by Eric Hall

September 14, 2013

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Donate A blog post came across my social network feed this week titled "15 Crazy Full Moon Facts." Oxford Dictionary defines fact as, "a thing that is indisputably the case." So I am not sure what the author of these "facts" was thinking, but it was far from anything factual. In fact, the post only has 14 "facts," which should have been a sign - but I kept reading. I felt I needed to counter each point - since my supermoon post has less than 500 views - while the post in question has over 5,000 shares between Facebook and Twitter alone.

If you believe the old wives' tales, male children are more likely to be born during full moons.

Since the sex of the child is determined at conception, the sex at birth couldn't be affected by the moon phase in any way.

More generally, there is a belief more babies are born during a full moon. While there is plenty of woo published out there trying to somehow tie the moon to child birth, there is no connection. Because this tale has been passed around for so long, people notice when it is a full moon and a baby is born. In 1994, 3706 non-induced births were analyzed, and it was found there was no correlation between the moon phase and labor.

A full moon is considered unlucky if it occurs on a Sunday and lucky if it occurs on Moon-day or Monday.

Really? Really? Well, I decided to see if any studies have been done on "luck" and the moon. Turns out because the belief is so strong, there have been studies on the moon cycle and medical outcomes. One study looked at both the moon and Friday the 13th affect on several types of surgery. The conclusion was:
Scientific analysis of our data does not support the belief that moon phases, zodiac signs, or Friday 13th influence surgical blood loss and emergency frequency. Our data indicate that such beliefs are myths far beyond reality.
Another study looked at over 2,000 lung cancer surgeries. A similar conclusion was reached:
Rate of intra-operative complications as well as rate of post-operative morbidity and mortality was not significantly affected by moonphases. Furthermore, there was no significant impact of the lunar cycle on long-term survival.
The moon has no significance in "luck," which should make sense because there is no plausible cause for an effect.

It's the only month of the year that can occur without a full moon.

It takes the moon about 29.5 days to go through a complete cycle of phases. So while this is technically a fact, it is a fact only because of our arbitrary shortening of the month of February. This is because it was usually the month chosen to be truncated in the past in order to realign the seasons when the calendar wasn't the right length to keep everything in the same place.

The term "blue moon" has nothing to do with the moon's color. It's the term used for the second full moon in a month.

Technically another "fact," but again has more to do with how the days are divided in our calendar than anything special. The most common definition used for "blue moon" is a second full moon in a calendar month.

Once a month, a full moon party erupts on the beaches of beach at Koh Phangan in Thailand where thousands of party goers dance until dawn

Tourists will look for any excuse to party.

The pull of a full moon is so strong that it causes tree sap to rise inside the trees. In certain areas, full moon harvests are avoided because the increased sap flow attracts insects.

As I pointed out in my supermoon post - the gravitational pull of the moon is not that much different whether the moon is in apogee or perigee - and both of these can occur during any phase of the moon. So it is possible that during some full moons, the pull of gravity is actually the weakest (though not much weaker than the strongest point). The difference in the net gravitational force would be insignificant to the sap in the trees.

(Edit: Also see note below)

Look closely at the full moon. It isn't round. It's actually egg shaped. The pointed end faces north.

Hey! A fact! I didn't verify the direction of the shape, but the moon does have an odd shape. In fact, it took until 2006 to really figure out how it got that shape. It turns out the moon had a pretty crazy orbit during its early formation.

One theory suggests that prehistoric men hunted according to the phases of the moon. Not because full moon nights are brighter but because they synchronized hunting time with their women's menstrual period and only came back from the hunt when sex was on the table again.

Much like with birth, the moon phases do not affect a woman's menstrual cycle. This is a classic case of misusing the word "theory." The proper term would be hypothesis - and a bad one at that.

The "honeymoon" gets its name from the full moon in June. Because this full moon fell right between harvesting and planting so it was considered the best time to get married.

I could find no reference to this Etymology. There were a few different possiblities suggested. One common one was because a honey derived drink was often served at weddings, the period after was called the honeymoon. There is also a 16th century poetry reference, similar to the idea that the first month of marriage would be the sweetest, like honey (and month being derived from the word moon).

A German study found that people are more likely to binge drink when there is a full moon.

This is a misrepresentation of the study. The study found that during the 5 days bracketing the full moon, there was an increase in the number of drunk driving arrests. I wasn't able to find the original study to look at the numbers or methodology, but even the news releases I could find didn't look at the number of drinks per hour (defining binge drinking), but simply looking at drunk driving arrests after the fact. As one article pointed out, it is very possible because of the myth of the full moon, it is possible police are more aware of and look for more drunk drivers during that time - meaning the data is a result of confirmation bias.

Philosophers like Aristotle claimed that the full moon exacerbated mental illnesses. And from these lunar theories of mental illness came the term "lunatic".

While the word etymology is true, the idea the full moon affects mental illness is total bollocks.

A UK study found that violent acts among prisoners increased in the days leading up to and away from a full moon.

I couldn't find this study. But much like other behavior, this study result likely is a result of confirmation bias and not the moon.

In England, more officers walk the beat during a full moon. That's because police stations report more crime on these nights than any other.

I found this tied to the article (The Daily Mail - I hated to link to them as they tend to be a terrible resource, but I had to give them credit for the quote below) about the binge drinking. Listen to how this is justified. According to one officer in the force:
"Last weekend we had a full moon and it was busier in Brighton than it has been previously.
An anecdote is not evidence. Many anecdotes is not evidence. This type of anecdote is exactly how the myths of child birth continue as well.

According to a Bradford Royal Infirmary review, your chances of being bitten by a dog during the full moon are twice as high as during other moon phases.

I was able to find this study. While one study is never the end of the discussion, because if it cannot be repeated it would seem the original study is wrong. I have a feeling something is wrong with this study, for the authors start with this premise:
The moon, ever present, will continue to influence different aspects of nature and humans. More studies are therefore needed to explore lunar effects on animals, especially their propensity to bite humans.
Human behaviour is altered during the full moon period
Earlier the authors claim earlier in the study that no study has shown a correlation for animals or humans in relation to the moon, then turn around and claim it as fact for humans. That is a big red flag that the study is likely flawed due to bias.


Don't fall for the myths of the moon. Enjoy it for what it is - a beautiful sight in the sky.



Some in the comments have pointed out the idea of the tides. The tides have a multitude of physical processes involved. One of the simplest ones to explain is the water's closeness to the moon. Gravity is proportional to 1/r. So the water on the side closest to the moon will feel more gravity than the side farthest away from the moon because it is about 12,600 kilometers farther away. This happens every day. The ocean is also huge and it is a fluid. As with many things in physics, it is about scale.

The apogee and perigee of the moon happens about every 15.5 days or so. This means these gravity differences don't follow the lunar phases and are on their own cycle. If any hypothesis were to have any plausibility, it would be to study the effect of those moon positions on certain events and physiology, not the phase of the moon. A quick search did not reveal any studies on those cycles. It is likely there would be no effect, because the force of gravity on an individual object on Earth is many times smaller than the Earth's gravitational effect.

by Eric Hall

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