Medical Astrology: Science, Art, and Influence in early-modern Europe

Specialist Medicine and Horoscopes

Explore: Specialist Medicine | Calculating a Horoscope | Drawing A Horoscope: Squaring the Circle | Understanding Aspects | From Aspect to Urine Wheels |Critical Days and Criticisms

Specialist Medicine

The horoscope was the hallmark of Specialist Medicine. Briefly defined, the word “horoscope” is used on this page to describe a drawing or diagram representing the positions of the planets and the signs of the Zodiac at a particular time and with respect to a particular place. Although introduced here as an exemplar of pointed prognostication, this celestial schema was, in fact, integral to a variety of astrological practices. At times, it even factored into the creation of annual wall calendars. Astrology historian Phebe Jensen explains that calendar compilers often refined their lunar- and solar-based forecasts by drawing horoscopes for the spring and fall equinoxes, and for the summer and winter solstices. These drawings, however, rarely—if ever—featured in the final calendar layout. A narrower view of the horoscope thus emerges from its archival, medical imagery. The primary source documents on this page instead align the horoscope drawing with private consultation, reflecting, in particular, three specialist horoscopic practices: nativities, elections, and interrogations. The drawings for each stressed different computational terms: nativities reflected the time and place of a patient’s birth; elections pinpointed propitious times to initiate important events, like medical treatment; while interrogations—which were used to answer a wide range of questions, including health-related inquiries—were drawn for the time and place that a particular question was posed. Given the complexity of each horoscopic rendering, this page will stress nativities, in particular, and direct readers desiring more information about elections and interrogations to the publications listed below.

Calculating a Horoscope

Calculating the various components of a horoscope required tremendous mathematical skill. Early-modern physicians, however, rarely reckoned each element by themselves. They instead relied on reputable ephemerides—like those published by Johannes Regiomontanus in the 1470s—which tabulated the day-to-day mathematical and zodiacal positions of the planetary bodies for a certain location over a several-year period. These positions were typically reckoned for a general time like noon or midnight; but, to produce a horoscope, more precision was needed. Physicians needed to map this information with respect to the time and place of a particular medical event: e.g., time of birth, onset of illness, etc. They realized these details with the help of two celestial and terrestrial constructs: the horizon and meridian.

The image at left from Peter Apian’s Cosmographia (1564) helps visualize both. The horizon—specifically labeled as such—is found between the Latin words Meridies at left, meaning “South” or “Midday,” and Septentrio at right, meaning “North.” Crossing the image horizontally, this negatively defined great circle divides the celestial spheres and, by extension, the terrestrial spheres into upper and lower hemispheres. The celestial meridian—here labeled Meridianus Mobilis or “movable meridian”—intersects the horizon perpendicularly at the aforementioned South and North points. Further passing through the celestial poles, this great circle conversely divides the celestial spheres and, by extension, the terrestrial spheres into Eastern and Western hemispheres. The meridian line (Linea Meridiana) along the bottom translates this celestial East-West division into fixed, terrestrial terms: we call it the Prime Meridian. Unlike this 0° longitude coordinate, the celestial meridian and the horizon are relative constructs. They vary according to one’s location on Earth, though always maintain their perpendicular relationship to one another. To better understand this relationship, notice the points at which both intersect the ecliptic—i.e., the Sun’s apparent orbit around the Earth. Now imagine this relationship with the Sun relative to your own location. The horizon always marks the position of the rising and setting Sun, while the meridian always marks the position of the noon-day Sun—regardless of location or time of year. What changes instead is their timing.

To quickly calculate this timing, select physicians turned to the astrolabe. This instrument easily figured the time of day or night at any time of year, though its use in medical practice was hardly common. Sundials and mechanical clocks, among other devices—like those displayed in the gallery below—satisfied most basic time-telling needs. According to historian Sara Schechner, few physicians would have used the astrolabe unless they served a person of high nobility, or even royalty. In this regard, the vellum-made, volvelle astrolabe from MS 26 (1553), below, is of particular interest. Compared to the brass “Hartmann Astrolabe” (1537) at right, this instrument is modest, inviting speculation about the class of clientele it may have served.

Although equipped with fewer features than the Hartmann Astrolabe, this vellum volvelle was still a precision instrument. A brief inventory of its parts reveals its two time-telling systems, as well as their relationship to the above-outlined constructs. The red cross at the top is equivalent to the word Meridies: it designates both time and direction, marking Midday as well as South. The number 12, directly opposite, marks Midnight. The red numbers lining the outer edge of the instrument, on either side, mark the Equal Hours: they divide the hours of day and night into two equal sets of 12 hours. By contrast, the curved black lines on the face of the instrument mark the Unequal Hours. Briefly defined, an Unequal Hour is one twelfth of the period between sunset and sunrise, or between sunrise and sunset; its duration varies with the season.

On the instrument, the Unequal Hours are indicated by the spaces between the curved black lines, which are numbered 1–12. The 0 and 12-hour lines—which correspond to the transition from black to red ink—mark the horizon; the 6-hour line—which aligns with the red-cross Midday/Midnight axis—marks the meridian. The rotating rete or dial on top of these lines represents the sky surrounding the earthly instrument-user, whose position coincides with the direct middle. The smaller circle, listing the Twelve Signs of the Zodiac, is the ecliptic. The animal figures are star pointers.* Their tongues, beaks, and other features point to a collection of fixed stars and constellations, whose positions are measured with reference to the ecliptic. Note: these positions are for the year 1553, not 2021. The figures in the outer circle point to stars that are—or were—south of the ecliptic. These include Mirach in the constellation Andromeda; Sirius in Canis Major; Denebola in Leo; and Alwaid in Draco. The inner-circle figures point to stars that are north of the ecliptic: specifically, Deneb Kaitos in the constellation Cetus; Alphecca in Corona Borealis; and Vega in Lyra. Together, they represent the heavens both above and below the horizon at any given time, thus allowing the astrolabe user to reckon time at night as well as during the day.

The takeaway from this technical information: the astrolabe is a time-telling device that illustrates correlation between the celestial and terrestrial spheres—a basic premise of the horoscope drawing. To this end, it was also particularly well suited: it made easy work of finding the horizon and meridian, as well as timing their points of intersection with the ecliptic. These points were the backbone of the early-modern medical horoscope.

* The dog- and dragon-head pointers—as well as the y-shaped rete—link this instrument to a very important English-language source: Geoffrey Chaucer’s A Treatise on the Astrolabe (1391). For more information on this astrolabe’s “Chaucerian design” see the essay by Catherine Eagleton cited below.

Click on any of the images below for more information.

Drawing a Horoscope: Squaring the Circle

The horoscope drawing is a pictorial chameleon. Its shape changes depending on context and convention for calculation. Although there are many different ways to delineate a horoscope, the early-modern medical drawing was typically square. However counterintuitive, this square represented the celestial spheres subdivided into 12 triangular spaces known as houses, domiciles, or mansions. Underpinning this architectural subdivision were the horizon and the meridian. As the seventeenth-century physician Richard Saunders (1613–1692) explained, “The whole Sphere of Heaven is divided into four equal parts, by the Meridian and Horizon, and again into four Quadrants, and every Quadrant again into three parts…So the whole Heaven is divided into twelve equal parts.” The horizon and the meridian are rarely named as such in the drawings themselves, though their locations are implied. Notice the numbers 1–12 in the figure at right: they reveal the horoscope’s underlying order, which always begins at left and then unfolds counterclockwise until 12. The houses labeled 1, 7, 10 and 4, appearing in the diamond at center, point to the perpendicular meeting of the horizon and the meridian. The apexes of houses 1 and 7 signpost the East-West line of the horizon, while the peaks of houses 10 and 4 mark out the South-North axis of the meridian. The directional orientation of the horoscope, then, is similar to the astrolabe. House 10 at the top of the drawing marks Midday as well as South, while house 1 at left pinpoints Sunrise as well as East. To give a concrete example: imagine a nativity drawn for a child born immediately after sunset. The physician drawing the horoscope would place the Sun in the lower part of house 7, just below the horizon. Along with geographic and temporal reference, however, each horoscopic house also harbored a host of other possible significations. Examples of these are featured in the gallery below. 

Click on any of the images below for more information.

In spite of their graphic uniformity, the horoscope’s twelve triangular houses accommodated a variety of significations. The images above show that each was aligned with one of The Four Elements—i.e., Air, Fire, Earth, Water—and their Four Elementary Qualities—i.e., Hot, Cold, Dry, Wet—as well as with one of the Twelve Signs of the Zodiac. Each also described different terrestrial domains that the celestial spheres might influence—e.g., house 11 is labeled “the house of good fortune” and “friends,” while house 9 is linked to “prayer & long journeys.” The images above also show that, of the twelve houses, seven were “home” to a specific planet, while ten were linked to different parts of the body. The color-coded horoscope at left, from Peter Apian’s Astronomicum Caesareum (1540), further shows that seven houses in particular were associated with matters of health. These included houses 1 and 7; 10 and 4; 6 and 8; as well as 12. Particularly inauspicious were houses 6, 8, and 12, which are respectively captioned the “House of Infirmity” [Do. Infirmitatis], “House of Death” [Do. Mortis], and “House of Imprisonment” [Domus Carceris]. More positive are houses 10 and 4—labelled Medicus and Medicina—which portended possible healing powers and treatments. Of course, a diagnosis was needed before treatment could be determined. Important in this regard were houses 1 and 7—labeled Infirmus Consultor and Infirmitas Questio—which respectively yielded information about the sick person and the nature of their illness. All of these significations and more, however, hinged on the horizon and the meridian: specifically, on their intersections with the ecliptic.

The most important calculation in the horoscope was the horizon’s Eastern point of intersection with the ecliptic, which—in early-modern, medical-astrological vernacular—was known as the Ascendant. Marked by the word “Ascendens” in the image above, this point is synonymous with the word “horoscopus” in Latin, which is, in turn, a loanword from Ancient Greek derived from the root words hōra (time) + skopos (observer). Like its antique antecedents, the early-modern term “Ascendant” specifically referred to the point of the ecliptic that was ascending over the Eastern horizon at a particular time and place. In the medical horoscope, it marked the time of a child’s birth, the onset of illness, etc. By contrast, the meridian’s point of intersection with the ecliptic—known as the Midheaven or medium coeli—marked the midday threshold between ascension and descension in the visible daytime sky. In the medical horoscope, it pointed to a sick patient’s physician and/or possibilities for treatment. These perpendicular positions were expressed in the horoscope drawing both graphically—by the apex of houses 1 and 10—and numerically in zodiacal degrees and sometimes, more precisely, in minutes. The manuscript image at right demonstrates this numerical denotation, documenting an Ascendant point sitting at 16° of Leo and a Midheaven at 4° of Taurus.* This image is one of 360 horoscope drawings featured in a manuscript edition of Johannes Engel’s Astrolabium planum (ca.1505), which was first published in 1488. Emphasizing the Ascendant position in particular, each drawing indicates one of the possible 360-zodiacal degrees at which the Ascendant might be found. The unique illustrations and Latin dictums accompanying each drawing further impart prognostications for each degree. The bridled donkey shown here is paired in the text with the words “Homo Indisciplinatus erit,” which ultimately puts forth a prediction about a person who was born as 16° of Leo was rising over the eastern horizon: namely, “Man will be undisciplined.”

* Note, in this example, the differing degrees for the Ascendant, Midheaven, and other horoscope houses. These varying degrees contradict the above-cited statement from Richard Saunders about equal-house division. Historian John David North, however, provides further clarification on this topic. He explains that for the best astronomers this method of equal division was too straight forward to be favored and thus led to an entire range of alternative methods. This manuscript image represents one such alternative.

Understanding Aspects

The position of the Ascendant was of paramount importance for a medical diagnosis. For the physician, it was one of three primary signifiers of the sick patient: the other two being the Moon, and the planet ruling the Ascendant’s zodiacal location—sometimes known as its “Lord.” The physician Richard Saunders provided clear instruction on this topic, writing in 1677: “for the Significators of the Sick Patient, take the Ascendant, his Lord, and the Moon, and that Planet or Planets, which by ☌, □, or ☍ afflicteth those Places, shall be the true Morbificant Planets, or Significators of Disease.” The three symbols Saunders cites are simply shorthand for different relationships that might exist among the planets. Collectively, these are known as aspects. Most early-modern, medical-astrological texts—Saunders’ included—describe five different aspects or relationships in total, which are pictured in the images at right. Although frequently anthropomorphized, these five aspects were primarily mathematical in nature. They represented different ways of subdividing the 360 degrees of a circle: e.g., by halves (180°), thirds (120°), quarters (90°), sixths (60°), etc. Of course, as the images indicate, this circle was not just any circle: it was the celestial spheres or, perhaps more specifically, the 360° of the ecliptic. Accordingly, these aspect relationships are often expressed in zodiacal rather than mathematical terms, which helps to explain the anthropomorphic qualities attributed to each in different interpretations. The video below highlights Peter Apian’s interpretation of the aspects in the Astronomicum Caesareum (1540). For contrast, Richard Saunders’ explanations are also cited below.

According to Saunders, the “five Aspects of the Planets” are “thus named and charactered: Conjunction ☌, Sextile ✶, Quartil □, Trine△, and Opposition ☍.” However, he adds that the Conjunction “is not properly called an Aspect, although for brevity sake we so term it.” He then further characterized each in the following manner:  
☌ The Conjunction, he explains, “is when two Planets are in the same degree and minute of Longitude…with good Planets this is the strongest good; with evil, the greatest evil.”
✶The Sextile, he explains, “is when two [Planets] are distant the one from the other two Signs, or sixty Degrees, or the sixth part of the Zodiack…this is an Aspect of Amity.”
□ The Quartil, he explains, “is when two Planets are remote three Signs, or 90 Degrees, or the fourth part of the Zodiack…this is an aspect of Enmity and Malignancy.”
△The Trine, he explains, “is when two Planets are elongated the one from the other, four Signs, the third part of the Zodiack, or 120 degrees…this is an Aspect of Friendship and Amity.”
☍ The Opposition, he explains, “is when two Planets or more are distanced apart by the space of six Signs, or 180 Degrees…this is an Aspect of the greatest Hostility.”

Despite emotional charge, these aspect relationships are based on fairly logical foundations. They point to the 30° of celestial longitude allocated to each of the Twelve Signs of the Zodiac, as well as to the combinations of the Four Elementary Qualities associated with each. Fire signs, like Sagittarius, were thought to be hot and dry; Earth signs, like Capricorn, cold and dry; Air signs, like Aquarius, hot and wet; and Water signs, like Pisces, cold and wet. Taking the Quartil aspect as example, the words “Enmity” and “Malignancy” associated with it thus describe a relationship like that between the cold-and-wet Pisces and the hot-and-dry Sagittarius. These words figuratively describe the extinguishing, intense incompatibility that exists between elements like Water and Fire, which are always 90° away from one another in the Zodiac Wheel.

Simply put: These five aspects vacillate between positive and negative significations. Unsurprisingly, then, the three that Saunders cited in reference to the sick patient—☌, □, or ☍—all point to potentially negative planetary influences. His instruction is to seek out the Planets that make such aspects to the Ascendant ruler, the Moon, and the Ascendant—in that order—in a patient’s nativity. These, he says, will be the planets responsible for producing disease and thus prove instrumental for arriving at a diagnosis. This instruction, however, raises a question when considered in relation to the illustrations above. If the aspects are to be understood within the context of the medical horoscope, then why are the aspect diagrams circular when the horoscope is square? One possible explanation: these two diagrams draw attention to two overlapping “house” systems—one celestial, the other terrestrial. The Twelve Signs of the Zodiac are thus tantamount to celestial houses, whereas the twelve triangular parts of the horoscope amount to terrestrial houses: i.e., they more specifically represent the nature and type of influences that the celestial spheres are expected to exert on the terrestrial realm.

Another aspect volvelle, pictured below, is unique to the copy of the Astronomicum Caesareum (1540) at the Medical Historical Library, Harvey Cushing/ John Hay Whitney Medical Library. Lying loose inside the back cover of this edition is the partially printed, partially hand-drawn and hand-colored aspect volvelle seen below. This page is a cancelled printer’s proof for page G III. The text blocks on the reverse display information otherwise dispersed across pages G III Recto and G IV Verso in the final publication. This is also the location in the text where the second dragon volvelle appears, previously pictured here. Unlike the dragon, however, this volvelle is not an eclipse calculator. The inner green and burgundy bands of numbers, which line the edge of the dial—pictured at left—instead mark the Equal Hours, much like the astrolabes above. Otherwise, the outer green band displaying the numbers 1–29 ½ appears to calculate the lunar, synodic month. Directly above this band’s first and final numbers, the words “Minuta Equationis Dierum” finally makes the volvelle’s purpose clear: this is a calculator for The Equation of Time.

Click on any of the images for more information.

From Aspect Wheels to Urine Wheels

Medical-astrological specialists routinely paired horoscopic interpretations with empirical observations to determine diagnoses. The most important practice, in this regard, was uroscopy—i.e., the examination of urine for symptoms of disease. The ubiquity of urinalysis at this time cannot be overstated. Under certain circumstances, physicians might even draw a horoscope for the moment when a patient’s urine was first brought to them for inspection. More commonly, however, physicians made recourse to uroscopy when horoscopic aspects pointed to more than one possible diagnosis. Richard Saunders stressed this strategy in particular, noting: “for although the Starrs do insinuate unto us these things more precisely than either Urine, Pulse, or Excrements…Ambiguity often ariseth,” thus making the cause of disease “very hard to find without the help of the Parties Urine.” “Therefore,” he explained, “the surest ground is not altogether to depend upon Astrology in the investigation of Disease, but also to require the help of Pathological means.” The images below echo Saunders’ sentiments, particularly the urine wheels at left and right. Linking the practice of urinary pathology to celestial hermeneutics, these images show that the urine vial—like the horoscope—was also a hallmark of specialist medicine.

Critical Days and Criticisms

Calling attention to the Astronomicum Caesareum’s contributions to medicine, Peter Apian wrote of his celebrated text in 1540: “So that one may understand even a little how astronomy is useful, I put an instrument on sheet M II, which doctors will know how to use, since it shows The Critical Days. That is, the days when Nature (if it otherwise tries) fights back against sickness. A wise doctor or one who understands such an instrument can signal [these occurrences] many days in advance and [this instrument] should thus be used.” Contrary to expectation, the instrument that appears on M II Recto in Apian’s text is not the black, green, and yellow Critical Days volvelle at right—which appears instead on M III Recto—but the colorful, square horoscope pictured above. No other instruments appear in between. If Apian’s reference to “the instrument on sheet M II” is a typo, then it is a useful one. It underscores the connection between the horoscope and the volvelle, highlighting the medical applications of both. The Critical Days volvelle at right, however, transforms the horoscope’s complex calculations and interpretations into an accessible twirling graphic. Apian made this graphic even more accessible by providing explanations for each of its parts in both Latin and German. A few key points from his German-language exegesis are translated here, starting with the device’s black cross. Principium Morbi, he writes, “means the beginning of the disease. This pointer should be placed in the degree where the Moon was when the illness started.” Crisis Prima, he then notes—advancing counterclockwise— “shows in the Zodiac the degree at which Nature will fight against the disease,” adding “if the doctor understands astronomy, he may well see how the same Crisis or battle between Nature and disease will begin.” He notes the power of planetary aspects to amplify or mitigate this first Crisis, which, he says, “usually occurs on the 7th day after the onset of illness.” Crisis Secunda, he then adds, “shows Nature’s second fight against the disease, and usually happens on the 14th day.” “Crisis Tertia is the third fight; it usually happens on the 20th or 21st day.” Between these four black pointers, he explains, are four green ones labelled Indicativa, which always show how the future and next crises will unfold, for better or worse. The first Indicativa, he explains, “usually happens on the 4th day after the onset of the illness, the next on the 11th day, the third on the 16th or 17th, and the fourth on the 24th day.” Between the green pointers are pink ones labeled Intercidens, which he says, “indicate the days in which malevolent moisture calls Nature to battle.” Finally, he notes “the remaining days, called Vacui, are those in which Nature stands completely still and does not act against the disease, for this reason [they are] also called the medical or medicinal days, since the sick person may surely and safely receive treatment at this time.”

With this artful graphic, Apian not only streamlined medical-astrological prognostication, but also clearly announced his position on a key medical debate of his day. Historian of science Glen M. Cooper explains that, during the fifteenth and sixteenth centuries, the Hippocratic Galenic doctrine of The Critical Days became the focus of a protracted debate among physicians, which divided those for and against the use of astrology in medicine. Representing the opposition and reform voices in this debate were well-known Italian philosophers and physicians, like Giovanni Pico della Mirandola (1463–1494) and Girolamo Cardano (1501–1576). Many of those advocating for astrology were elsewhere in Europe or England: they included German mathematicians, humanists, and astronomers, like Apian, as well as physicians and philosophers like Federik Grisogono (ca.1472–ca.1538) from Zadar (Croatia). Grisogono’s advocacy for the use of astrology in medicine, like Apian’s, focused on issues of forecasting and prognostication. Pictured at left is the graphic volvelle from the final pages of his second book, De mondo Collegiādi: Pronosticandi, & Curandi Febres (1528). Whereas Apian’s volvelle stressed the location of the Moon, Grisogono’s device emphasized the fixed stars: his was a device for diagnosing the humors involved in fever and for predicting the development of disease by the stars.

Apian and Grisogono's volvelles made manifest the movements implied in the medical horoscope drawing. Replacing celestial calculation and conceptualization with graphic annotation, their devices offered readers easy access to medical-astrological methods of pointed prognostication. They invited learned, intellectually curious audiences—beyond the narrow scholarly elite—to engage with their ideas on astrology in medicine. Apian even admitted as much at the start of the Astronomicum Caesareum, writing: “We see how much mathematics are hated because of their seeming difficulty. We tried to simplify and began to plan by what new methods the remedy would be found and be a help to those, whom arithmetic has baffled up until now. Astronomy does not repel. It asks to be understood. If the universal theory of the heavens is reduced to instruments without the use of numbers and calculations, it would be a great help to those who have studied long.” Apian’s transformation of mathematics into graphics found great favor, in particular, with Holy Roman Emperor Charles V (1500–1558), who granted him the right to display the arms pictured at right in 1535. Apian’s graphical transformations, however, were not celebrated by all. Johannes Kepler (1571–1630), for example, composed a particularly scathing appraisal of Apian’s achievements in 1609, writing:

Who will provide me with a source of tears to bewail the misdirected efforts of Apianus, who in his Opus Caesareum, as a faithful servant of Ptolemy, has wasted so many fine hours and so many highly ingenious thoughts on a highly intricate maze of spirals, loops, lines and whirls, which represent nothing more than what exists in the imagination of man, and is wholly divorced from nature's true image. His work demonstrates one thing only, namely, that this man, with God's gift of a profound and penetrating intellect, could have mastered nature. Instead he was satisfied and even pleased that he had invented those artificial constructions (in competition with nature herself) and that he had succeeded in making those mechanical models. In doing so, he has earned the prize of lasting fame, but let us not forget the damage he has caused by the success of his works; and what shall we say about the empty art of producers of automatons, who used 600 or even 1200 wheels in order to produce the figments of human imagination, and who, gloating in triumph about their achievements, were claiming prizes because of them.*

Kepler's words, dripping with disdain, rebuke Apian for concealing his mathematics behind ingenious, short-cut graphics. They accuse Apian of eliding the difference between fact and fiction, of alienating the users of his volvelles from the experience of actual celestial engagement and study. Ultimately, Kepler's cynicism inspires a final reminder about this exhibition: all of the images featured here have been cut from their original contexts. Parties interested in these illustrations—and in medical astrology in general—would do well to revisit this exhibition's primary source documents and continue researching the ideas with which its images are associated. An extensive list of primary and secondary sources are provided on the subsequent page (see: Bibliography). While  digitized sources have been linked whenever possible, all of the works in this exhibition can be found on Yale University's campus: in particular, at the Medical Historical Library, Harvey Cushing/ John Hay Whitney Medical Library.

* Johannes Kepler, Astronomia nova, Chapter 14 (1609), quoted and translated in Derek J. de Solla Price, “Review: The Book as Scientific Instrument,” Science 158, no. 3797 (6 October 1967): 104.

 

Works Cited on this Page
Apian, Peter. Astronomicum Caesareum: Eine Grüntliche außlegung des Buchs Astronomici Caesarei [A Thorough Exegesis of the Book The Emperor’s Astronomy.]. Ingolstadt: Apian, 1540. (See Diij Verso)
Barnes, Robin Bruce. Astrology and Reformation. Oxford; New York: Oxford University Press, 2016.
Boršić, Luka; Skuhala Karasman, Ivana. “Frederik Grisogono, the iatromathematician.” Croatian Studies Review 12 (2016): 21–43.  
Cooper, Glen M. “Approaches to the Critical Days in Late Medieval Renaissance Thinkers.” Early Science and Medicine 18, No. 6 (2013): 536–65
de Solla Price, Derek J. “Review: The Book as Scientific Instrument.” Science 158, No. 3797 (6 October 1967): 104.
Eagleton, Catherine. “Chaucer’s Own Astrolabe: Text, Image, and Object.” Studies in the History and Philosophy of Science 38 (2007): 303–326.
Eisner, Sigmund. “Building Chaucer’s Astrolabe—II, III.” Journal of the British Astronomical Association 86 (1976): 125–132; 219–227.
Gaida, Margaret. “Reading ‘Cosmographia’: Peter Apian’s Book-Instrument Hybrid and the Rise of the Mathematical Amateur in the Sixteenth Century.” Early Science and Medicine 21, No. 4 (2016): 277–302.
Ionides, S. A. “Medieval Astronomical Constants,” Publications of the Astronomical Society of the Pacific 46, No. 274 (1934): 325–38.
Jensen, Phebe. Astrology, Almanacs, and the Early Modern English Calendar. London; New York: Routledge, 2021.
King, David A. In Synchrony with the Heavens, Volume 1: The Call of the Muezzin. Leiden; Boston: Brill, 2004.
•    See also: King’s essay on the astrolabe: “The Astrolabe: What it is & What it is not (A Supplement to the Standard Literature)” (Frankfurt, 2018).
North, John David. Horoscopes and History. London: Warburg Institute, University of London, 1986.
Rutkin, Darrel H. Sapientia Astrologica: Astrology, Magic, and Natural Knowledge, ca. 1250–1800. Archimedes 55: New Studies in the History and Philosophy of Science and Technology. Cham, Switzerland: Springer, 2019.
Rutkin, Darrel H. “Understanding the History of Astrology (and Magic) Accurately: Methodological Reflections on Terminology and Anachronism.” Philosophical Readings 7, No. 1 (2015):  42–54.
Saunders, Harold N. “The Simplified Construction of the ‘Unequal’ Hour Lines on an Ordinary Astrolabe.” Journal of the British Astronomical Association 90 (1979): 54–56.
Saunders, Richard. The Astrological Judgment and Practice of Physick. Deduced from the Position of the Heavens at the Decumbiture of the Sick Person: Wherein the Fundamental Grounds thereof are most clearly displayed and laid open: Shewing by an Universal Method not only the Cause, but the Cure and End of all manner of Diseases incident to humane Bodies. Also diverse notable Experiments, of great use to all the Insutrious Students in Physick and Astrology. London: Printed for L. C. and to be sold by Thomas Sawbridge at the three Flower-de-luces in Little Britain, 1677.
Schechner, Sara. “Astrolabes and Medical Travel.” Chapter 13 in The Art, Science, and Technology of Medieval Travel, 181–210. Aldershot, UK: Ashgate, 2008.