Astrology and Medicine

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Astrology and Medicine


Astrology is a form of divination based on the assumption that the motions of the heavenly bodies influence human affairs. Therefore, astrologers claim that they can predict the future by observing and interpreting the positions of the stars, sun, moon, and planets. During the Middle Ages, the relationship between medicine and astrology was very close. Medieval astrologers blamed disease epidemics on dangerous combinations of the planets and studied the motions of the heavenly bodies as a guide to the treatment of individual patients. The practice of astrological medicine required knowledge of the astrological correspondences among the seven planets, the seven metals, and parts of the body. Even in the twenty-first century medical astrology practitioners continue to claim that they can predict potential illnesses and select the best time for surgery.


Astrologers believe that by interpreting the influence of the heavenly bodies they can predict the future of individuals, groups, or even nations. Astrology originated in ancient Mesopotamia as a system of observing and characterizing celestial omens. Various forms of astrological doctrine eventually found their way into Greek, Roman, Indian, Egyptian, and Islamic worlds. Plato's (428-348 b.c.) Timaeus became the foundation of nature-mysticism by developing ideas about the divinity of the heavenly bodies and their direct relationship to life on Earth. The Timaeus expressed the concept of man as a microcosm. Despite his general opposition to mysticism, Aristotle (384-322 b.c.) aided the development of Western astrological theory by proposing that the world of movements in the sublunary sphere (beneath the orbit of the moon) was determined by the movement of the celestial bodies, which were guided by divine influences. The group of philosophers known as the Stoics provided further grounding for astrological ideas.

During the Middle Ages, Western Europe was strongly influenced by classical Greek astrological doctrines that had been incorporated into Islamic scholarship. European interest in astrology was stimulated by the translation of Arabic texts and astronomical tables into Latin during the twelfth and thirteenth centuries. By the fifteenth century, European scholars were able to study new translations made directly from the classical Greek texts.

Throughout the Middle Ages, the terms astronomy and astrology were used synonymously in reference to knowledge of the stars. The modern distinction between astronomy (the science of the stars) and astrology (the art of divination by the stars) evolved very gradually. Some astrological theories assumed the existence of a totally mechanistic universe, which left no room for free will or intervention by a deity. Such forms of astrology were rejected by Christian and Muslim theologians because it went against their religious beliefs. Other forms of astrology postulated that the movement and position of the heavenly bodies merely provided information about possibilities that could be altered either by divine intervention or resisted by human will. Christian theologians argued that the determinism inherent in astrology was incompatible with the Christian belief in freedom of will, but they accepted the general concept that astral influences affected the sublunary sphere. Fatalistic or deterministic forms of astrology were rejected and banned. Human beings might be influenced by the stars, but by wisdom and will they could escape the fate predicted. Broad areas of astrology, including medical astrology, were accepted along with the system of rules that determined the proper moment for undertaking various actions and for distinguishing between propitious and unpropitious days.

The special relationships that existed among the heavenly bodies and the earth were regarded as extremely complex. Thus, errors in astrological prediction were to be expected. Astrology was used to inform individuals about the course of their lives, based on the positions of the planets and the zodiac signs (the 12 astrological constellations) at the moment of birth or conception. This form of astrology was called genethlialogy or judicial astrology, the casting of horoscopes. Other astrological techniques were used to determine whether or not a particular moment was propitious for the success of a given course of action. This form assumes that an individual could choose to act at astrologically favorable times and avoid misfortunes predictable from the casting of a horoscope.

The revival of ancient learning and the growth of universities during the European Middle Ages stimulated interest in astrological doctrines and the practice of astrological medicine. In the late European Middle Ages many distinguished universities, including Paris, Padua, Bologna, and Florence, had chairs of astrology. Classical astrologers assumed the existence of a geocentric universe in which the sun, moon, planets, and even the stars revolved in circular orbits around the earth. Throughout the European Renaissance and the Reformation astrology remained a part of the university curriculum, despite the challenge that Copernican theory posed for the geocentric worldview.


During the Middle Ages, the ties between astrology and medicine were quite strong. The belief that the heavenly bodies influenced human fortunes was widespread. Physicians were expected to take astral influences into account when dealing with each patient. In addition, the physician had to understand the general influence of the heavenly bodies on medications and parts of the human body.

Medical astrology, which was also known as iatromathematics, was based on the assumption that the motions of the heavenly bodies influenced human affairs and health. An important premise of medical astrology was the correspondence between the 12 signs of the zodiac and the organs or parts of the human body. Each section of the zodiac acted on the corresponding part of the body by means of its association with a particular stellar force. Particular positions of the planets therefore affected the functioning of the body. Such astrological considerations could be applied to individuals or to whole populations. For example, the outbreak of bubonic plague in 1348 was attributed to a malign conjunction of Saturn, Jupiter, and Mars.

Astrological medicine required knowing the exact time at which the patient became ill. With this information and a study of the heavens, the physician could prognosticate the course of illness with mathematical precision and avoid dangerous tendencies. Doctors were guided by their knowledge of the astrological correspondences among the seven planets, the seven metals, and parts of the body. Physicians could cast retrospective horoscopes to identify the configurations of the planets that had caused diseases and epidemics. Physicians also had to incorporate the astrological concept of the "medicinal month" into their plans for treatment of the patient. The concept of critical days could be traced back to Hippocrates (460-377 b.c.), who frequently marked the number of days after the onset of illness on which certain zodiac signs appeared. Eventually, computations involving numerical relationships among calendar dates, critical days, the motions of the moon, and favorable and unfavorable days became part of astrological medicine. The complexity of the system and uncertainties in determining the exact moment of conception, birth, or the onset of illness could be used to explain errors in prognosis.

In therapeutics, astrological considerations determined the nature and timing of treatments, the selection of drugs, and the use of charms. For example, the sun ruled the chronic diseases, Saturn was blamed for melancholy, and the moon (a very changeable planet) influenced the outcome of surgery, bleeding, purging, and acute illness. Because the moon governed the tides and the flow of blood in the veins, the surgeon was well advised to consult an almanac in order to study the configuration of the heavenly bodies before performing therapeutic bleedings. Astrological practitioners might also recommend that a patient should wear a specific talisman containing an appropriate astral image engraved on a precious stone. However, the presumed relationships between the heavenly bodies and the human body were so complex, numerous, and contradictory that in practice it was impossible to carry out any operation without breaking some rule.

European acceptance of Greek and Islamic astronomy and astrology during the twelfth century encouraged the development of medical astrology. Until sophisticated planetary tables were available, the application of complex astrological calculations to medical practice was inhibited. The peak of medical astrological practice in Europe probably occurred between the fourteenth and sixteenth centuries. Far from being seen as superstition, astrology seemed to link the practice of medicine to the world of science and mathematics. Astrology was seen as part of the intellectual basis of medical education. Learned medicine included medicine, logic, natural philosophy, and astrology. Physicians studied Latin texts at the university, but even surgeons, who were generally not associated with universities, studied medical and astrological texts.

Medicine and astrology were often combined in the careers of the most prestigious and prosperous physicians, in particular those who served wealthy and powerful patrons. Demonstrating competence in astrological computations was considered one of the ways that a learned physician could separate himself from an empiric or quack. The most ambitious medical students were particularly likely to study astrology and mathematical calculations at the most advanced level possible. Graduates of the university went on to write treatises on astronomy and astrology, improve the design of astronomical instruments, and prepare new astronomical tables.

By the seventeenth century, as the world of science was transformed by the works of Copernicus (1473-1543), Galileo (1564-1642), Johannes Kepler (1571-1630), René Descartes (1596-1650), and Isaac Newton (1643-1727), astronomers rejected and repudiated astrology. Since the Scientific Revolution, astrology and alchemy have been defined as occult systems whose basic doctrines are incompatible with modern science. Popular belief in astrology, however, has continued undiminished into modern times, as is evident in the articles and horoscope found in the newspapers and the flood of almanacs and astrology manuals found in bookstores.


Further Reading


Barton, Tamsyn S. Power and Knowledge: Astrology, Physiognomics, and Medicine under the Roman Empire. Ann Arbor, MI: University of Michigan Press, 1994.

Cornell, Howard Leslie. Encyclopaedia of Medical Astrology. York Beach, ME: S. Weiser, 1992.

French, Roger. Practical Medicine from Salerno to the Black Death. Cambridge: Cambridge University Press, 1994.

Kibre, Pearl. Studies in Medieval Science: Alchemy, Astrology, Mathematics, and Medicine. London: Hambledon Press, 184.

Klein-Franke, Felix. Iatromathematics in Islam. Hildesheim, NY: G. Olms, 1984.

McBride, M. F. Chaucer's Physician and Fourteenth Century Medicine: A Compendium for Students. Bristol, IN: Wyndham Hall Press, 1985.

O'Boyle, Cornelius. Medieval Prognosis and Astrology. Cambridge: Welcome Unit for the History of Medicine, 1991.

Shumaker, W. The Occult Sciences in the Renaissance; A Study in Intellectual Pattern. Berkeley, CA: University of California Press, 1972.


French, Roger. "Foretelling the Future: Arabic Astrology and English Medicine in the Late Twelfth Century." In International Review Devoted to the History of Science and Its Cultural Influences 87 (1996): 453-480.

Hare, E. H. "Medical Astrology and Its Relation to Modern Psychiatry." In Proceedings of the Royal Society of Medicine 70 (1977): 105-110.

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Astrology and Medicine

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