5X5 Episode 79

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5X5 Episode 79
The Lunar Effect
14th October 2009

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5X5 78 5X5 80
Skeptical Rogues
S: Steven Novella
R: Rebecca Watson
B: Bob Novella
J: Jay Novella
E: Evan Bernstein
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The Lunar Effect[edit]

Voice-over: You're listening to the Skeptics' Guide 5x5, five minutes with five skeptics, with Steve, Jay, Rebecca, Bob and Evan.

S: This is the SGU 5x5 and we're talking about lunar madness or the lunar effect. Does the full moon affect human behaviour? There is a persistent urban legend that it does. That crimes increase, that ER visits are increased, and that suicides are increased and that generally a host of human behaviours are affected by the lunar cycle. However, it turns out that when these statistics are carefully examined, pretty much with every specific claim, there is no detectable and replicable statistical effect. It turns out that the lunar cycle doesn't really have any significant effect on human behaviour. Now, the justification that is typically given for the lunar effect is that the moon can affect the tides—the moon does affect the tides of the earth because of the differential gravitational pull on the various parts of the earth, and that it could have a similar tidal effect, therefore, on the human brain, which is floating in spinal fluid. However, that argument really has no plausibility, because the tidal effects depend on the difference in the distance from the object. The diameter of the earth is almost 8,000 miles at the equator, so that's from one side of the earth to the other, so that's a significantly difference in terms of the distance to the moon. But one side of your head to the other, we're only talking about a matter of inches, so there is no significant tidal effect on your brain from the moon. Some have held out that there is still an effect because of the different light from the moon. So, that has some plausibility—on a full moon you have a well-lit night and people might be more likely to go out and do stuff. Whereas on other times of the month, there would be less light. But if there is a significant effect from that, no one has been able to detect it.

E: And for as long as there has been cultures and civilisations, there has been the moon involved with the development of those cultures and just about everything they do. Everything from what they plant, where they fish, how they harvest and how they hunt, predictions and things that they make. But as we have come over the centuries and millennia to understand the moon in a more scientific context and have a better grasp of that knowledge, at the same time we still to still cling to a lot of the superstition and otherwise pseudo-science that is associated with the moon having certain effects over different aspects of our lives. Certainly more psychological than practical or physical.

B: The full moon has spawned many myths and legends in folklore in many cultures. One that persists to this day is that the full moon can drive people insane. The word "lunacy" is one obvious result. Now this superstitious belief has collided and merged with others such as Lycanthropylycanthropy, or werewolves, which go as far back as ancient Greek mythology, which describe lycan, who changed into a wolf after eating human flesh. Modern myths and cinema describe werewolves as ordinary men most of the time until the light of the full moon magically forces their often painful transformation into werewolves.

R: Actually, a new study[1] was just published very recently saying that the full moon does not have any effect on surgery outcomes. It was quite a large study that's been published in the October issue of the journal Anesthesiology[2] and researchers looked at more than 18,000 patients undergoing elective coronary artery bypass graft surgery between 1993 and 2006 and they found that the phase of the moon did not affect mortality rates or anything like that. So, apparently you don't have to worry about the phase of the moon when you go in for surgery.

J: So Steve, to further what you were saying, a lot of people think that since the moon has such a dramatic effect on the tides, that it must also have a dramatic effect on the human body. A lot of people think the human body is made out of a high percentage of water, and therefore that same liquid would be moved by the moon in some manner that would affect us. But the lunar force is actually considered to be a very weak tidal force. So as an example, a mother holding her child will exert 12 million more times as much tidal force on her child as the moon would.

E: Wow.

S: Yeah, that really puts it into perspective. It's one of those so-called back-of-the-envelope calculations where you're throwing out possible explanations like tidal forces, but if you just try to figure out what the order of magnitude is, you realise that it's not happening; it's not going to have any effect, physiologically. Also, the other thing that always struck me is that tidal forces aren't really that closely linked to the lunar phases, right? I mean, when there is a so-called new moon, the moon and the sun are in the same direction, so there is no light reflected from the moon back to the earth. The moon is still there exerting a tidal effect, so the only real connection between the phases of the moon and the tides are how the solar and lunar tides line up. Not really the magnitude of the lunar component of the tides themselves.

B: Maximum tides would be, like you said, at the new moon, when we can't even see the moon, but we are lined up sun, moon, earth.

S: So there should be myths about the effects of the new moon on human behaviour, but there isn't. Only the full moon. Which suggests that it's not—has nothing to do with gravity or tides and in fact, it may just be as Evan said, all cultural, psychological and persistent legend that probably is not going to go away any time soon.


S: SGU 5x5 is a companion podcast to the Skeptics' Guide to the Universe, a weekly science podcast brought to you by the New England Skeptical Society in association with skepchick.org. For more information on this and other episodes, visit our website at www.theskepticsguide.org. Music is provided by Jake Wilson.

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