Lunar Light as a Trigger for Werewolf Transformations

By Scott Mattison (@FoolsPizza)

Most people are familiar with the idea of a werewolf, a human with the ability to shapeshift into a wolf or humanoid wolf monster.There are many variations of the concept of a werewolf, but most versions center around the notion that the full moon acts as the catalyst for the transformation. Completely ignoring the fact that such a transformation would require a rapid reorganization of several body systems, the time has come to ask the hard question: Are there any unique properties of a full moon that could cause such a transformation?

Now, you may be thinking that werewolves are magic, and clearly there is no need for science to try to explain magic. However, as scientists, it is important to question the unknown and develop a deeper understanding of our world. While werewolves may not be real, it is still fun to think of the answers as a what if scenario. [As a side note, if there is an entire magical community running around like in the Harry Potter books, they are colossal jerks for not sharing all of the medical breakthroughs that magic would bring.]

Does the full moon possess any unique qualities that could trigger the transformation from human to wolf? In many descriptions of werewolves, lycanthropy is a curse passed down by the bite of another werewolf. This curse may be some form of virus, similar to rabies, but I will leave that discussion to those more suited towards it.

As a general note, some stories involving werewolves treat the transformation as a timed process that occurs with the cycle of the moon, regardless of the presence of moonlight. Timed processes such as this are called lunar rhythms. Lunar rhythms are really neat, but this blog post will focus more on the moon and moonlight itself.

Most stories of werewolves involve the transformation typically only occurs at night during a full moon. The fact that the transformation only occurs at night is very important as full moons are often visible in the daylight. In fact some months, the full moon occurs entirely during the day. This tells us one of two things 1) it is not the shape of the moon that is triggering the transformation or 2) bright sunlight acts as an inhibitor to the transformation process.

Furthermore, many accounts of the transformation describe the individual only changing after being bathed in moonlight, and not requiring the individual to look at the moon. This observation further supports the idea that the shape of the moon is not triggering the transformation process. Confirmation of the existence of a blind werewolf would be required to fully confirm this theory. However, finding such a specimen may prove challenging.

This leads us to the idea that moonlight is what acts as the primary catalyst for the transformation. It is very possible for a virus to introduce an optically sensitive component to cells of the body. In fact there is a whole field of science, known as optogenetics, which allows scientists to introduce light-based control of muscle and nervous cells through genetic engineering. In that case, what is special about the light of a full moon? Well, during a single lunar cycle, lunar brightness increases exponentially as the moon waxes and decreases exponentially as the moon wanes. This means that during a lunar cycle, the full moon is the brightest. 

There are two big issues with the hypothesis of lunar brightness. The biggest issue is that if the transformation is caused by a brightness threshold alone, then a werewolf would transform anytime they walked out into the sunlight, as the moon is simply reflecting the light of the sun. This actually relates back to one of our observations earlier, bright sunlight may act as an inhibitor to the werewolf transformation. This would mean our virus is introducing some form of optically sensitive molecule that is activated at a certain threshold of light, but deactivated in some way by bright sunlight.

Sunlight blocks the transformation of a person into a werewolf.

This isn’t too far fetched as the sun is roughly 400,000 times brighter than the full moon. Alternatively, there could be some spectral shift of the light reflected by the moon relative to the sun that triggers the transformation. The moon isn’t a perfect reflector and does absorb some wavelengths more strongly than others. The reduction of one wavelength beneath a certain threshold may be the requirement for the transformation to occur instead.

The second biggest issue is that the brightness of the full moon varies between lunar cycles depending on the angle between the moon and the earth, the distance between the moon and the earth, and the presence of small particles in the atmosphere. Interestingly, these changes are noteworthy because they do actually coincide with certain descriptions of werewolves.

Some accounts of werewolves describe the potential for the change to occur on the days preceding and following a full moon. This could be due to the moon being closer to the earth (so that it takes up more of the sky) or at a point higher in the sky (so that it is traveling through less atmosphere). Furthermore, many accounts of werewolf encounters describe the transformation occurring as the moon appeared from behind the clouds. This is in agreement with the theory that a certain optical threshold must be reached to cause the werewolf transformation.

In conclusion, we propose that lycanthropy is caused by the introduction of an a molecule that responds to light into the host’s cells. This molecule is activated by light above a certain intensity threshold and inhibited by the presence of bright sunlight. Thus, if werewolves are real and follow the rules discussed above any individual who has been bitten by a werewolf need only to wear a thick layer of sunscreen on the nights leading up to and following the full moon to prevent their transformation.

Author’s Note:

Major Spoilers for “Harry Potter and the Prisoner of Azkaban” Follow so if you haven’t read a 19 year old book (or watched a nearly 14 year old movie) stop reading here

My wife and I had a long debate on whether or not the werewolves in the Harry Potter books follow lunar rhythms. Through most of the books it is implied the transformation occurs whether or not the individual is exposed to moonlight during a full moon, thus implying a lunar rhythm. However, in the third book Lupin doesn’t transform until the moon comes out from behind a cloud and bathes the party in moonlight; implying moonlight is the catalyst for the transformation. So either the cloud moment is just meant as dramatic flair and he would have transformed at that exact moment either way (which could is probably true, but annoyingly coincidental) or the cloud moment is the answer and Lupin should never transform if he simply locked himself in a basement or dungeon. Either way we were definitely overthinking the whole situation.