MadSci Network: Astronomy

Re: Is man affected psychologically and/or physically by lunar cycles?

Date: Sat Mar 4 06:41:00 2000
Posted By: Joseph Lazio, Radio Astronomer
Area of science: Astronomy
ID: 951423072.As

I contend that the answer is yes and no.

Some people will travel hundreds, even thousands of kilometers to watch a total solar eclipse in which the Moon passes in front of the Sun. Professional astronomers routinely ask for dark time, i.e., time during the new Moon, for their observations. (The reason is that the light from the Moon can make it more difficult to see faint objects. Compare the difference in the brightness of the sky between new and full Moon some month.) Clearly these are examples in which the phase of the Moon affects people's behavior.

However, when people talk about the effect of the Moon, they are typically referring to the idea that X increases during the full Moon, where X is crime, births, or some other aspect of human behavior. (The word lunacy is derived from luna, the Latin word for Moon.) I am aware of almost no evidence to support this belief, despite ardent support for it from police officers and emergency room and OB/GYN nurses. For instance, the late astronomer George Abell examined the birth records from LA hospitals for over 10,000 natural births (i.e., no C-sections). He could find no correlation between the number of births and the phase of the Moon.

The accepted explanation for this perceived effect is a human tendency to find order where there is none. After a particularly busy shift one night, a police officer or nurse will notice a full or nearly full Moon. The full Moon can be such a brilliant sight that it is easy to see how one might think there would be an association. Humans also have a tendency to forget contrary evidence. Thus, the police officer or nurse will not remember the last busy night that was during a new Moon (after all it is difficult to see the new Moon!). From this start, it doesn't take long for one to become convinced that the full Moon might have an effect on humans. This belief might also become self-fulfilling. For instance, a police officer might become less tolerant of minor offenses during the full Moon (and the additional light provided by the full Moon might help him/her see more). Another contributing factor might be people's inability to tell when the full Moon actually occurs. When I was teaching astronomy, I had a student tell me that the first-quarter Moon was full.

I've also been told by a futures trader that recommended practice is to buy during one phase and sell during another. Although he thought it was a result of the phase of the Moon influencing the buying and selling, I think a more simple explanation is that this practice is apparently what they are taught (perhaps resulting from the same kind of misconception that produces the crime and birth myths).

(I'm not picking on police officers or nurses. I've just heard this belief expressed most strongly from them, and their professions can require them to be up late at night, when the full Moon is most likely to be noticed.)

Another common belief is that the human female's menstrual cycle is influenced by the phase of the Moon. There are two problems with this belief. First, the average woman's menstrual cycle is 28 days, which is close to the orbital period of the Moon, but is not exactly equal to it. The range of menstrual cycle lengths, though, is quite large. I've heard of women having cycles as short as 21 days and as long as 52 days. If the Moon controlled or influenced the length of the cycle, it is not clear why the range would be so large. Second, other major mammels do not have a cycle close to 28 days. In particular, the length of the cycle for chimpanzees, our closest relative species, is 35 days (if I remember correctly).

For more information, you might want to try to find any book on pseudoscience edited by Martin Gardner.

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