15 Crazy Moon Fallacies

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/r². 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. 

About Eric Hall

My day job is teaching physics at the University of Minnesota, Rochester. I write about physics, other sciences, politics, education, and whatever else interests or concerns me. I am always working to be rational and reasonable, and I am always willing to improve my knowledge and change my mind when presented with new evidence.
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33 Responses to 15 Crazy Moon Fallacies

  1. Jon Richfield says:

    Hey Eric, you say: “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” but given a 38-week pregnancy (nine lunar months, and a pretty common pregnancy duration) a child born at full moon is likely to have been conceived at full moon and the gravitational effects on the fertilisation process might well favour the lighter Y-bearing sperms, right?
    Complex stuff, biology, especially when SEX rears its ugly head…

    • Eric Hall says:

      First the acceleration caused by gravity isn’t affected by the mass of the object. The FORCE is different, but the acceleration is equal. (I can’t get my equation image to show up here – I will post elsewhere if you need me to show the algebra on how that works).

      Now if we deal with your size issue – this depends on the shape and how the density is distributed. But if we assume a circular cross section to the direction of travel, and assume the density is uniform we can figure the following – doubling the mass will only increase the cross-sectional area by roughly 1.5 times. Thus the drag force doesn’t increase as quickly on the larger sperm. Thus an additional acceleration should actually allow the larger sperm to get there faster, not the smaller because the one twice as massive has twice the moon force, but 1.5 times the drag force at the same velocity.

      If one were to hypothesize which sperm would get there first due to the moon, it would be the female sperm, not the male sperm. The reality is the force and acceleration are so small compared to all the other forces experienced by the sperm, it can be ignored.

      • Jon Richfield says:

        Oh gosh Eric; quite right! But then of course I was quite right for the opposite reason; those hasty, massive female sperms get fooled by the gravity and overrun the target, right?
        But let’s see: falsifiability, must have falsifiability! I predict that as a result there would be a tradition of a greater frequency of… etc etc…
        How’s that for scientific virtue?

        • Gustav says:

          Aren’t all human fetuses originally female before some modify into males? [I am obviously not a biologist but I do recall reading that.] Therefore, the ‘Y’ chromosome has more mass…

          Ah, another myth is born. [I want credit (and a royalty) every time someone runs with this myth.]

          Interesting post, Eric, thank you.

          • argent47 says:

            The Y chromosome is smaller than the X, with less mass, and it conveys less total information than the X. But it does carry the crucial information for modifying the initially female-type structure into the male type.

          • Moral Dolphin says:

            male – female is determined by the sex chromosomes. The fetus is way after that.

            The ovum always carries an “x” chromosome (It has an entire extra complementary DNA set in the mitochondrion which sperm doesnt have).

            The sex of the eventual mammal (lets not get snobby here!) is determined by the sperm cell that fuses with the ovum.

            This is because the “haploid” cells (ie half cells) formed by the female always has “x” chromosomes and the male has either “x” or “y” sex chromosomes.

            The biological sexism ends just about there until some rat starts pulling ones pigtails in pre school.

            One special point, the ovum carrying all the ancillary cellular material passes on the mitochondrion in subsequent cell reproduction. MtDNA is matrilinear.

            Mind you, there are a whole raft of conditions where male-female, extra chromosomes etc produces problems after this.

            Probably not “fagged out sailors leaving the rest of the seamen in the hold” (Eric take note or you may actually be on DIY should Mrs Eric find it a bit odd that you want to “fill” the wrong organs wrt to oceanic volumes. Just goes to show that hanging around with chemical engineers may give you a slanted view on reproduction. )

            (I always make sure there isnt a calculator on my desk, for safety reasons!)

            Damned that at my age I have to start posting about sex.

      • Moral Dolphin says:

        And I was going to comment about sex being on the table amongst our forebears

        a) If you have a solid table, its perfectly safe no matter what phase the moon appears to be in.
        b) Food wouldnt be on the table any way
        c) Table? Hunter gatherers in clans had tables? Thats like saying the scots have a cuisine!

        The moon whether being in any phase or not has little effect (gravitationally or magnetically) greater than the pillow at the other end of your neighbours house (lights on or off).

        But if you want to make some biological claim, some critters and plants may have evolved to travel, flower, seed during particular phases (if you fish you will immediately understand that) and some fellers may or may have not been at home (cave etc) but were out hunting.

        What a sexist society we live in though! What moron suggested that in a pre religious pre marital clan like society the women didnt have a say about what time it was to cut the grass (so to speak).

        Sadly, if you even read the bible, you’d understand that matriarchy made all the naming rights. This “one on one” man is the focus in a relationship is a very recent fad that hopefully is dissapearing from the notions of science and out of the community.

        Yes “monogamy” as viewed is beneficial to both sexes for social reasons. But its practice is fairly well intrdispersed with liasons that fit in with our timetables of opportunity.

        The moon has nothing to do with that and if its safely practiced on a sturdy table there is a very good chance it isnt even in a monogamous table. (Mooning aside).

        My secretary and I would like to apologise to the staff and patrons at the miranda wood fired pizza restaurant for the events a fortnight ago…

        It was that stunning venus in the north west at sunset!

        Try getting the police off your back in this suburb!

    • Evan says:

      Aside from the fact that any gravitational differences would be trivial, once again, the phase of the moon is independent from the distance to the moon. Some full moons are at perigee, some at apogee, most somewhere in between. So gravity cannot have anything to do with it–the tidal effect is absurdly insignificant at that scale.

      • Eric Hall says:

        This is true. A full moon gravity is no different than new moon, first quarter, last quarter, or anything in between for a given distance. The moon being full has nothing to do with the amount of gravity. Perhaps I will restate that in the post for clarity.

    • Toni says:

      Actually, Jon…I am quite sure you are correct…That and a few other things such as the moon affecting the tides…water…humans being 75% water…fetus’ being in amniotic fluid…things like that also play a factor..Anyone who has ever worked in an Emergency Room or Labor and Delivery…KNOWS…a full moon plays a major part in admissions…In fact…admissions double during a full moon!!!!!!

      • Eric Hall says:

        My wife also works in labor and delivery – and that rumor about more deliveries at the full moon is total nonsense that continues to be propagated like truth.

        In fact this data has been studied – “The different phases in the lunar cycle and especially the full moon do not appear to have any influence over the distribution of deliveries in this study.” Ref: http://www.ncbi.nlm.nih.gov/pubmed/15648892

        The confusion comes because there is a misunderstanding of how the gravitational force works. The ocean is a much larger body of water than a lake, than a puddle, than a person. The ocean can have tides of a couple meters, Lake Superior has tides of a few centimeters, and a puddle has no noticeable tides. There is not enough mass of water in a human to have a significant change in gravitational force due to the full moon.

        The other thing to note is that the tidal effects have nothing to do with the phase of the moon. The moon is overhead every day. Look up during the day of a new moon phase and you will see the moon in the daytime sky (assuming atmospheric conditions allow for it). This is no different than the full moon and in fact is why there are two high and low tides every day. It is nonsense to think the full moon provides some special force not present every other day.

  2. Doug Mathias says:

    Eric, I am unable to comment because the moon phase isn’t right . . .

  3. Reg. says:

    “The pull of a full moon is so strong that it causes tree sap to rise inside the trees.”

    Yair but …. in a cold winter environment in say, Europe, would several nights of bright moonlight cause a slowing in the rate of falling sap levels? That’s extended brightness rather than gravitational pull of the moon and possible reason to dance about in glee. If you’ve been in Bergan Norway, on the longest day of the year, you’ll know what I mean, especially if the phase of the moon is right. They clear the street for 30 minutes between 5 and 5.30am so the street sweepers can rush about, then the party resumes.

    • Eric Hall says:

      The temperature is due to the clear conditions, not due to the moon being out. You see the moon because it is clear, thus people often incorrectly correlate the weather and the moon.

  4. Peter G Brooksbank says:

    All you say maybe true Eric but there are two things I would like to add. The first is the well known fact that tides are affected by the pull of the Moon and after nearly sixty years on this rock I still find that strangely impressive.

    The second contradicts your assessment of the moon not affecting behaviour.

    Let me say first and foremost that I am not a criminal, I am reasonably well educated and hold down a good job. I also have never had the compulsion to do anything untoward or injurious to anyone or anything and do not get involved in strange practices at the time of the full moon or at another time for that matter.

    However I find the moon, particularly at full beguiling in a way that I have never understood. Even in childhood I was fascinated by the moon. In my teens and twentiesI would go up onto the moors, to the sea or out into the countryside to see the shadows and shapes that the moon would make and the moonlit moors have a special fascination for me.

    For the last forty years I have tried to book my holidays in conjunction with the full moon. Driving along a country lane at night with the moon leading is a thrill for me.

    I like to see an eclipse of the moon and many years ago I awoke in the night only to see the full moon partially eclipsed in through a skylight, I found it quite striking.

    I don’t now why, the interest has never wained and I can’t explain it.

    There is a short story by Guy de Maupassant were a man in a boat goes out at the time of the full moon on the river seine, it holds a special fascination for me.

    In reality the moon dosent make me do anything but I find it strange as an adult that it attracts me like a moth to a flame.

    Can anyone explain this fixation?

    • Eric Hall says:

      The tides are different because of the scale. If the uterus were filled with an ocean volume worth of semen, I would then consider some effect on pregnancy.

      • innominata says:

        Are you calling for double blind trials?

        • Moral Dolphin says:

          If you dont look, I wont look..ant I’ll try as hard as I can possibly can to be reasonably productive.

          This is the Benny Hill smut chat?

          Just to be sure we are on the same page (or tables), this doesnt require a double blind trial unless you want to test the pill.

          Requesting lights out is sufficient.


          “If the uterus were filled with an ocean volume worth of semen”

          Volumetrically aside here..I think I see your obsession with over doing things (to “If the uterus were filled with +++++++++++ of semen”).

          I know we blokes take this efficiency thing just a bit too far but what you wrote is positively interfereing and reliably unromantic.

          Buy flowers, chocolates, nice wine and a nurses uniform. Let nature get the critters home.

    • Eric Hall says:

      As far as your fascination with the moon, that would be like anyone’s fascination. Certainly we wouldn’t claim Star Wars has some gravitational effect on people, yet there are people who plan their vacations around standing in line for movies, going to Comic Con, etc.

      Certainly people like Phil Plait and Neil deGrasse Tyson have a fascination with the moon and other features of space – so much so they’ve made careers out of them. I think if you ask them, they will say it has nothing to do with anything physiological from gravity or light.

    • Reg. says:

      ” … and do not get involved in strange practices at the time of the full moon or at another time for that matter.”

      As far as you know?

      Boom boom boom boom boom.

      What is strange to you may be normal to me. [Looking carefully around.]

    • Moral Dolphin says:

      This is bizarre that I meet someone who is precisely like me. I book my holidays for the last quarter so I miss people like that.

      I’d get a safe convection heater if I were you.

      PS remind Brian that we have a mothman candidate!

  5. Reg. says:

    … or is it possible there is an electrostatic field on the surface of the Earth that follows the position of the Moon, whether in phase or phase shifted from the tides? Even the Moon could find any field existent on its surface and capacitively coupled to the Earth, increased or decreased depending on Solar winds or radiation. What then the happy indolent sperm and their detractors?

    • Moral Dolphin says:

      I am dead sure that there is a bit of terran electrostatic field woo about somewhere. Its enough to make your hair stand on end.

      If Brian hasn’t covered this I am sure there would be the odd entry in the skept email talk (look at the communities menu) or in the JRef forums.

      Brian has covered thunder storms somewhere. A brief trot through his episode guide should reveal it.

      Until its cleared up, never shake hands with an astronaut.

    • Eric Hall says:

      If it existed, it would be an incredibly small charge. It would also cycle daily as the earth rotated and would have nothing to do with the phase.

      • Reg. says:

        I guess so, I just love the super low frequencies we choose to ignore, like one cycle per day as the Earth sweeps around leaving the charge in a fixed relationship to the moon. The Moon is the reference and it’s the rotation of the Earth that changes the phase. 360 degrees a day +/- a little bit ‘cos the Moon slips. (?)

        Then I think about the mythical people who have lived permanently in the middle of a continent and the fear generated by venturing to the edge of the land and beholding the sea and tides for the very first time. Slapping fore-head, “How long has this been going on?” Do you get it? All durations are seem as relative to the duration of the life of a human being. How quaint.

        But the real quandary is how continual central core heating of the Earth compares with that from the 12 hours of Sunlight. Again the Solar heating cycle is +/- 12 hours but the core frequency is probably one cycle per umteen million years. But the super super doozie is whether we have yet completed just ONE single rotation of the centre of the Milky Way. Or will we ever? Now that’s a LOW frequency.

        By the way I’m still out here sitting cross-legged on the North Star looking back at the North Pole with a few casual glances at the centre of the galaxy because there’s not much to look at behind me. A bit warm here despite being on the outer edge of the Milky Way.

        Signed; The First Dr Hu.

        • Argent47 says:

          Earth’s core temperature is not cyclic, though the convection currents in the upper mantle do cause local variations in the subsurface temperature. Solar heating of the surface is as nothing, compared to the deeper temperatures.

          The galactic rotation period is estimated as 200 million years, so we’ve definitely “been around the block a few times”.

          In keeping with the ongoing sexual lunacy here, I’ll just say that, because of that slow galactic rotation, our current position in the cosmos has been a long time coming.

          • Moral Dolphin says:

            Pedant post here..

            If you see the moon over head (or on the horizon etc) it will be more than 24 hours before you see it in that position again.

            About 1/28 * 24 hours…

            Its one of the facts (supported by observation) that I use to get folks to work out which way the moon rotates around the earth in its orbit.

            To think people take their holidays for this sort of thing.

          • Reg. says:

            200 million years has got to be my new favorite low frequency then. I’m surprised, only 200 million, I’m glad I found that out before I die.

            With the Earth’s core I was thinking one creation to the next. So how deep in Permafrost at the poles and why doesn’t the core temperature do something about it?

            And why are we even bothering with this puny moon?
            Oh yair, the tides and the whales and randy women.

          • Reg says:

            From MD

            About 1/28 * 24 hours…

            “Its one of the facts (supported by observation) that I use to get folks to work out which way the moon rotates around the earth in its orbit.”

            I like that Sex Rat, oops … something I should have thought about before, and again, something I should have thought about before. So it IS slipping relative to the rotation of the Earth, moving from W to East? That’s good and it’s so easy to think it’s the other way.

            I had the same experience someone else mentioned; looked out the Western window at 4am one morning, and there was the moon with the Earth’s shadow across it. SHE wasn’t interested, in the MOON I mean.

            Is that pedantic enough?

  6. Moral Dolphin says:

    That would leave them plates apart, not poles apart. (oh Dear, we are back on that sturdy table with the secretary again). Look, there was just oup for a snack. The fork was intended for later!).

    Can we look into this bizarre notion that people have of sperm. Ive noted that they are viewed as critters swimming in a direction looking for eggs.

    Maybe a skeptoid on sex education would be useful here.

    This has started out with a great deal of humour and should be harvested for creationists to get the jokes as well.

    • Reg. says:

      Plates apart is closer than Poles apart but they all wander about anyway.

      Do you mean the wood fired Pizza joint that used to have Mahogany tables but chopped them up after you and your secretary absconded? No more testosterone topping for you. EVER!!!

      • Moral Dolphin says:

        Look Reg, it was a small lunacy.

        Wandering about though…Must be the simplest monte-carlo sim one could ever do!

        Thats the sailors (not me getting caught again).

  7. Moral Dolphin says:

    I think that just about covers our “frat boy” contribution to skepticism. Eric writes a multi-point essay on mooning and all we can talk about is sex..

    We’d have to ask other skeptical comments groups about our style points for the episode.

    I am going to do the dusting now. Its a purple feather duster from Franklins. Sadly, I’ll be doing it im my slovenly trakkies and ugboots and will be avoiding the kitchen table till lights out.

    Thanks Incominata for the double blind and handcuffs suggestion..

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