Hektoen International

A Journal of Medical Humanities

Blood under the moon: the role of astrology in surgery

Margareta-Erminia Cassani
Michigan, United States


Zodiac man, showing the astrological connection to the body
Zodiac Man, Homo Signorum, from Guild Book of the Barber Surgeons, c 1486, BL MS Egerton, 2572, f. 50v.  Luminarium:  Encyclopedia Project

Imagine your doctor telling you that you need surgery. Then they follow that unsettling news with something, well, a little strange sounding. They tell you that the date picked for your surgery needs to occur during a waning moon to control bleeding. After you have stared blankly at them for a few moments, you may wonder if they have gone over the moon and not in a good way.

And yet that is exactly what physicians and surgeons of early antiquity and the barbers of medieval and Renaissance days advised their patients. That is because since the days of ziggurat-building and sky-god worship in Mesopotamia up until the eighteenth century, physicians and surgeons also studied and practiced astrology. They believed that the phases of the moon exerted a critical influence on human blood flow, particularly the full moon phase, and thus it was critical to know when it would occur. Additionally, the astrological sign the moon was transiting through on a particular date and time,1 determined the best date to perform surgery and bloodletting (a practice that originated in ancient Egypt).2

Many learned and reasonable people might believe that these ancient doctors were our modern-day equivalent of quacks. Yet, should we apply that judgment to Hippocrates, the highly esteemed ancient physician regarded as the father of medicine? Or the equally esteemed Galen?3 Hippocrates, who penned the medically responsible dictate “First, do no harm4 was himself an astrologer. Hippocrates taught that all disease originated from the physical realm. But he also taught his students something seemingly contradictory to his renowned medical knowledge and teaching: he also believed in the influence of astrology to manipulate human health. He is quoted as saying (in various translations), “He who does not understand astrology is not a doctor, but a fool.5 Hippocrates believed in the value of a physician’s understanding of astrology in order to be a better doctor, and that surgeons, particularly, should be well versed in the phases of the moon and its assistance in controlling blood flow and other bodily fluids, or “humors,” in performing surgery.

But astrological medicine, or “iatromathematics,6 was not just a study of early Mesopotamian, Egyptian, or Greek doctors whom later physicians might write off as naïve or superstitious. The practice persisted far into medieval days when a new type of medical practitioner, a barber7 stepped onto the medical scene. Barbers were crude surgeons of dubious backgrounds with very little formal medical or surgical training. They were commonly consulted for their bloodletting services, a common method of treating disease, as well as perhaps hacking off a diseased leg, foot, or other body part. They too were taught to consult an almanac as well as the Tractatalus Hypocratis8 to plan surgical events9 in order to avoid the full moon and, possibly, their client bleeding to death.

When the Renaissance rolled around and scientific knowledge was making remarkable advances in understanding the treatment of human illness, when Leonardo DaVinci contributed remarkable knowledge of the anatomical functioning of man with his cadaver autopsies,10 astrology was still instrumental in treating human disease and performing surgery. Even Nostradamus, the noted high Renaissance soothsayer/astrologer, was a renowned physician in Paris.11 He regularly charted the astrological transits of the moon and other planets in treating his patients. But the importance of astrology to the practice of surgery and medicine did not end in the Renaissance. It continued far into the eighteenth century when an aspiring doctor could not even get into a university without also knowing astrology and its effects on human health.12

Today’s universities no longer require students to know medical astrology but there are many new-age practitioners who support the return of its practice.13 Today it is more of a niche service practiced by skilled astrologers. It is a quite complicated endeavor to determine surgical or other treatment dates for clients. That is how I became interested in medical astrology and its impact on human health. My former, late fiancé was a master astrologer who, in addition to casting a client’s astrological chart for general knowledge of their personality, best place to live, best job, romantic or partner compatibility, would also on occasion be asked to cast the best dates for surgical procedures. He taught me how moon phases and the moon’s transits through each astrological sign and other astrological aspects work in devising the best surgery dates. Prior to his teaching, I had spent years as a medical researcher in the traditional down-to-earth realms of study, but found looking into the universe for astrological paths to human health quite fascinating.

Medical astrology is far more complicated than the scope of this essay can detail, but I would like to give you the basics of how it works in determining the best dates for surgery:

First, let us start with the moon in general. You would never want to perform surgery under a solar or lunar eclipse, unless in an absolute life or death emergency. In medical astrology, the sun rules the human life force and the moon governs the flow of fluids in the human body. An eclipse is a cutting off of energy. So, surgery under a solar eclipse could result in death and a lunar eclipse could create blood or fluid blockages resulting in deadly clots or swelling.

The phase of the moon is critical in controlling bleeding. Even non-superstitious surgeons have a saying, “Never do surgery under the full moon.” Studies have tried to refute this belief as a superstition but anecdotal stories of nurses and physicians in emergency rooms or operating rooms during the full moon may tell a more accurate story.14 But why would not the full moon have an effect on bleeding? We know that the full moon can affect the tides of the oceans, lakes, rivers, and streams of the world. The human body is over 50% water. Plasma, the largest constituent of blood, is about 90% water.15 Is it such a stretch to think that the human body could be affected by the pull of the full moon?

According to medical astrology, you will bleed more under a full moon. A recent study out of Rhode Island Hospital reported that your chances of surviving an acute aortic dissection are far better under a waning than a full moon.16 The study did not compare the amount of bleeding patients had under either moon phase, but a medical astrologer would likely ascribe their higher rate of aortic surgery success during the waning moon to decreased bleeding.

Next, medical astrology considers the body part being treated and its ruling zodiac sign to determine surgery. So with our aortic dissection patient, you do not want the moon to be transiting through the zodiac sign of Leo, a fire sign, which rules the human heart, aorta, and other circulatory vessels. To do so could invite a lot of inflammation or infection, i.e. fire, in the blood vessels and tissues. You would not want to perform heart or vascular surgery under a Leo transit unless it was an absolute life-or-death emergency, which aortic dissections frequently are. Ideally you would wait until the moon transited into Virgo, a stable earth sign. Earth smothers fire so surgery under Virgo would discourage inflammation and infection. And with a waning moon there would be much less blood loss. Virgo also rules the stomach, intestines, spleen, and nerves. As the aorta runs very near the abdomen, a surgeon would need to be wary of nicks to any of these structures as well. But since a surgeon’s hands are also steadied under an earth sign like Virgo, the surgery should go without accident.

Like Leo, each of the remaining eleven zodiac signs govern specific parts of the human body. Whatever part of the body the surgery entails, a surgeon would then avoid a moon transit through its ruling sign. Some medical astrologers also include the surgeon themselves, but others focus only on the patient, the body part’s ruling sign, the moon phase, retrogrades, and eclipses to exact a successful outcome.

Surgeons would also try to choose a time of day when the moon is not void as actions can be nullified. A void moon could mean a procedure did not take or necessitates a return to surgery for a re-do. And no surgery during a Mars or Mercury retrograde as Mars rules surgeons and Mercury rules communication. If either are retrograding, or rotating backwards, surgery could result in surgical errors or fatal miscommunication between medical personnel.17

Obviously, emergency surgeries cannot be held to astrology dictates. One can only pray for a good outcome. And trying to schedule surgery at a particular time and date is also difficult when operating rooms are run by very tight boarding schedules. A surgeon would have to be most persevering in their efforts.

Would I have surgery under a full moon or the other detrimental astrological aspects noted here? Given a choice, no, I would not. Here is why. For centuries, astronomers, scientists, physicists, and even farmers who plant their fields by astrology, have reported that the moon and sun, planets and stars exert a massive amount of transformative energy on the Earth. Why that same powerful energy would not also affect our human body, and every other living thing on the Earth, just seems illogical.


End notes

  1. https://www.ancient-origins.net/history-ancient-traditions/medical-astrology-moon-fever-and-diseases-sent-skies-009356
  2. https://www.history.com/news/a-brief-history-of-bloodletting
  3. http://www.greekmedicine.net/whos_who/Galen.html
  4. https://www.crystalinks.com/hippocrates.html
  5. Ibid.
  6. https://www.occultopedia.com/i/iatromathematics.htm
  7. http://broughttolife.sciencemuseum.org.uk/broughttolife/people/barbersurgeons
  8. “Tractatulus Hypocratis Medicorum Optimi de Aspectibus Planetrum Versus Lunam”, Pietro D’Albano,, 1516.  The aspects of the planets, moon, for the best of physicians.
  9. https://www.bl.uk/collection-items/guild-book–of-the-barber-surgeons-of-the-city-of-york
  10. https://www.artcrimearchive.net/single-post/2013/04/24/Leonardo-da-Vinci-and-Dissection
  11. http://www.discoverfrance.net/France/Features/Nostradamus.shtml
  12. https://www2.le.ac.uk/offices/press/think-leicester/health-and-medicine/2014/medieval-medicine-and-the-practice-of-astrology
  13. Ibid
  14. https://www.physicsforums.com/threads/surgeries-in-full-moon-and-new-moon.415316/
  15. http://givingblood.org/about-blood/blood-components.aspx
  16. https://www.sciencedaily.com/releases/2013/07/130715141816.htm
  17. https://exemplore.com/astrology/Astrology-and-Surgery-When-Not-To-Perform-A-Surgical-Operation



MARGARETA-ERMINIA CASSANI, MA, CMLS, has been a medical editor and writer for over 20 years and lives in Michigan (USA). She has many published articles in health and wellness, as well as creative writing, in both print and online venues. Margareta won 2 creative writing awards for fiction in the past and is currently working on a fictional book about the 1960s. Her interests include medical astrology, painting, and electric guitar playing.


Winter 2020  |  Sections  |  Surgery

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