Astronomical Instruments in the Middle Ages: More than just a timepiece

By Sophie Andrade

While astronomical instruments could be as useful to the medieval person as Google Maps is to us today, you pretty much needed a whole degree in mathematics to figure out how to use them properly.

Several different groups of people in the Middle Ages would have interacted with astronomical instruments at some point in their lives. Students used the instruments at university, monks invented and used them in monasteries, physicians used them to cast horoscopes for patients, and travellers likely used them on the road.


Many instruments, such as compass dials, sundials, and navicula, were primarily used for timekeeping, while other instruments like the astrolabe and the quadrant were used to track the heavens and predict the position of the planets and stars. In addition to these practical uses, astronomical instruments elevated the status and credibility of their owners by acting as symbols of knowledge, ingenuity, and style.


The Carolingian Renaissance brought about the establishment of universities, and the new computus curriculum provided a better understanding of astronomy and its instruments. Learning with an instrument was not uncommon, and perhaps the best-known evidence for instruments and learning comes from Chaucer’s Treatise on an Astrolabe, written in 1391, which describes Chaucer giving the instrument to his 10-year-old son as he prepares to attend university. It was written in the vernacular instead of Latin, which made it accessible to a much wider audience, and it describes the parts of the astrolabe and how to use it in detail.


In addition to this treatise, there is evidence in academic library catalogues that the instruments were used in the university libraries where they were shelved and borrowed in the same manner as books.

The library records from Merton College, Oxford, 1320-1340 show that their instruments were sometimes even more valuable than their books. In the mathematical books section, two astrolabes are listed, one priced at 13 shillings 4 pence and the other at 10 shillings. Chaucer mentions astronomical instruments in the Canterbury Tales when he describes an astrolabe lying next to books and ‘augrym stones’ on an Oxford student’s bookshelf. Without providing an explanation of what these instruments are, he implies that they are common tools for a student in the fourteenth century. These instruments would have been familiar to his audience and recognized as essentials for astronomical study.

Astrolabes were especially useful for study because they could calculate the rising and setting of the planets and the location of the stars and sun without the need to go outside. Students also likely learned with astrolabes and quadrants rather than other instruments, as their many uses, and mathematical nature, made them practical for teaching both geometry and astronomy.

Using astronomical instruments improved students’ knowledge and thus improved their status in society. Being a practiced astronomer, or someone who understands how to use an astronomical instrument, provided opportunities for respectable employment. University graduates could look for a patron and become a court astronomer, or they could enter a monastery and join the ranks of renowned astronomers and inventors.



Monks used astrolabes and other astronomical instruments too, particularly for calculating the hours of the day for prayer. They also relied on their instruments to calculate the time of Easter and other moveable feasts. The clergy followed canonical hours, and their days were divided into times for prayer. The rise of monasticism and specifically the spread of the Rule of Saint Benedict solidified these prayer hours into a system called the Divine Office, which consisted of seven specific times for prayer during the day and one at night.

In the early seventh century, sundials began to appear on church walls to aid monks in keeping to canonical hours while also reminding lay people, when they passed the clock, to take a moment to pray. They were used by astronomers, mathematicians and theologians alike to determine the dates of Easter and eventually create the Gregorian calendar.

By the mid-fourteenth century, Benedictine monasteries were ordered by the papal office to send at least one monk in twenty to a university, where they mainly studied theology and canon law, but would have also had opportunities to study other subjects including mathematics and astronomy. Although not all monks went to university, they were still able to engage with astronomy and its instruments within their cloister. Those who did attend university could bring back books to keep in the monastic library, where they were available for all to read.

Richard of Wallingford pointing to a clock, in reference to his gift to the abbey. British Library Cotton Nero D. VII, f.20

Richard of Wallingford, a fourteenth-century Benedictine monk, was one such monk who was able to attend university for an extended period of time and created some very influential instruments while he was abbot of St Albans Abbey.

Orphaned at age ten, Richard was taken in by the prior of Wallingford and then attended Oxford University for nine years.  He became abbot of St Albans in 1326 and, as an advanced mathematician, he invented two astronomical instruments as well as an immense astronomical clock.

He invented two instruments: the Albion, an instrument used to find the position of the planets, and the Rectangulus, an advanced astrolabe that was used for spherical trigonometry. His third invention, a great astronomical clock called the machina mundi, was admired centuries later by John Leland when he visited St Albans in 1540. Leland described the mechanisms of the clock by writing, ‘One may look at the course of the sun and moon or the fixed stars or again one may regard the rise and fall of the tide’. This was certainly an impressive instrument that was no less wonderful to its observers two hundred years after its creation.


Astrology and the movements of the planets were thought to have great influence on a person’s life. It was part of a physician’s duty to consult the heavens and take their positions into account when diagnosing and treating a patient.


Astrolabes were likely only used by royal physicians since they were so expensive, and much cheaper almanacs could be used in a similar fashion. These almanacs, or folded almanacs, while not technically astronomical instruments, should be noted for their presence in the world of medieval medicine. They were usually about twelve to twenty pages long and they appeared most commonly in England in the later Middle Ages. They would often have calendars of movable feasts, lunar tables, calendars of lunar and solar eclipses, diagrams of urine vessels, instructions for making astrological predictions, as well as diagrams of the Vein Man and the Zodiac Man.

A Vein Man is a diagram of a man which shows the location of veins and arteries, while a Zodiac Man is a diagram that labels the body with the signs of the zodiac in the locations over which they were believed to have influence. These almanacs were likely used by physicians of all levels and while they were designed to be worn hanging from a belt, they were more likely carried around in a protective case.

‘The Zodiac Man’, c. 1488, National Library of Wales, MS 3026C.

At the University in Bologna in the 1320s, an astrologer named Cecco d’Ascoli began his lectures by claiming astrology was an integral part of the study of medicine, and medical astrology became particularly popular in Italian universities in the fourteenth and fifteenth centuries. Most physicians would have had at least a surface knowledge of astrology in order to treat patients and take their horoscopes.

More often than not, physicians would retroactively diagnose or explain an illness based on previous horoscopes rather than predict imminent illnesses in the future. They would do this by determining the time of their patient’s birth, figuring out their horoscope and comparing it with the current position of the celestial bodies. From there they were able to interpret how the positions of the planets might have affected their patients in the recent past.

Travellers and Pilgrims

Astrolabes and other instruments were also used by travellers such as pilgrims and merchants. They could use their instruments to measure the distance to certain objects of a known height, determine the time of day, and from there determine when it would get dark. Astrolabes especially were perfect for determining a journey’s length and when one should stop to find shelter.

The Practica geometriae by Dominicus de Clavasio c. 1346 describes how an astrolabe can be used for many practical things while travelling, such as determining the ‘distance between the summits of two mountains, the length of a valley, or the distance between the foot of a mountain and its summit’.

Sundials, however, were likely more popular with travellers due to their smaller size and affordability. Sundials are one of the oldest astronomical instruments, dating back to 1500 BCE. Portable versions of sundials were popular among travellers, especially universal sundials which worked at different latitudes.

Using a table inscribed on the sundial, the traveler would determine their latitude based on which city they were in (or closest to) and adjust the angle of the dial. ‘Pin-gnomon’ dials found the length of daylight hours so travel could be planned accordingly. If the dial came with a device called a lunar volvelle, the traveler could use it to determine the amount of moonlight hours expected for that season as well.

Merchants and tradespeople would likely have used such instruments while conducting their business, as the rise of urban centres, trade, and the merchant class gave new meaning to the passage of time: to waste time was to waste money.

Despite this wide array of people, social classes, and usages, the owners of instruments all had these things in common: their instruments gave them knowledge, prestige, and a chance to show off their wealth and interest in astronomy. The student is identifiable in the Canterbury Tales by his instruments and owning them was a symbol of learning and accomplishment.  Monks who used and invented instruments, like Richard of Wallingford, brought renown to their monasteries and were regarded as the most gifted men of their time. Astrolabes lent a sense of wonder to the physician’s art as their knowledge of the human body and its ailments was proven through their use of instruments and almanacs. An astrolabe or sundial with several latitudes inscribed upon it proved how widely one had travelled and, if the device had been used for pilgrimage, it could also prove how devout one was. Any astronomical instrument represented knowledge and learning, and sometimes wealth, and along with their practical uses, they symbolised their owner’s power, status, and deep understanding of medieval astronomy and the heavens.

Sophie Andrade is a recent graduate of the University of St Andrews with an MLitt in Medieval Studies. Her research focuses on medieval women, music, manuscripts, and castles. She lives in Nottingham, England.

Further Reading:

Chaucer, Geoffrey. ‘A Treatise on the Astrolabe’, Internet Medieval Sourcebook, Fordham University (2020)

Chaucer, Geoffrey. Canterbury Tales. Harvard’s Geoffrey Chaucer Website. Harvard University (2020)

Carey, Hilary M. ‘What is the Folded Almanac? The Form and Function of a Key Manuscript Source for Astro-medical Practice in Later Medieval Europe’. Social History of Medicine 16 (2003), pp. 481-509.

Eagleton, Catherine. ‘John Whethamstede, Abbot of St. Albans, on the Discovery of the Liberal Arts and their Tools. Or, Why Were Astronomical Instruments in Late-Medieval Libraries?’ Mediaevalia 29 (2008) pp. 109-136.

Eagleton, Catherine, ‘What were portable astronomical instruments used for in late-medieval England, and how much were they actually carried around?’ in Joshua Nall, Liba Taub and Frances Willmoth (eds), The Whipple Museum of the History of Science: objects and investigations (Cambridge, 2019), pp. 33-54.

Falk, Seb. “I Found This Written in the Other Book’: Learning Astronomy in Late Medieval Monasteries’. Studies in Church History 55 (2019), pp. 129-144.

Gimpel, Jean. The Medieval Machine: The Industrial Revolution of the Middle Ages (London: Pimlico, 1993).

Giralt, Sebastià. ‘Astrology in the service of the crown: Bartomeu de Tresbens, physician and astrologer to Pere the Ceremonious of Aragon’. Journal of Medieval History 44 (21 November 2017) pp. 104-129.

McCluskey, Stephen C. Astronomies and Cultures in Early Medieval Europe (Cambridge: Cambridge University Press, 1998).

Schechner, Sara J. ‘Astrolabes and Medieval Travel’ in Robert Bork and Andrea Kann (eds.), The Art, Science, and Technology of Medieval Travel (Aldershot: Ashgate, 2008) pp. 181-210.

Schechner, Sara J. ‘The Material Culture of Astronomy in Daily Life: Sundials, Science, and Social Change’ JHA 32 (2001) pp. 189-222.

Schechner Genuth, Sara J. ‘Astrolabes: A Cross-Cultural and Social Perspective’ in Roderick and Marjorie Webster (eds.), Western Astrolabes: Historic Scientific Instruments of the Adler Planetarium & Astronomy Museum vol. 1 (Chicago: Adler Planetarium, 1998) pp. 1-25.

Siraisi, Nancy. Medieval and Early Renaissance Medicine: An Introduction to Knowledge and Practice (Chicago: University of Chicago Press, 1990)

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Top Image: Astrolabe – Falcon® Photography / Flickr