32 Are humans affected psychologically and/or physically by lunar cycles?
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This article is from the Astronomy FAQ, by Joseph Lazio (jlazio@patriot.net) with numerous contributions by others.
32 Are humans affected psychologically and/or physically by lunar cycles?
By Joseph Lazio <jlazio@patriot.net>
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
mammals 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.
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