Microscope image of a nervous system tumour alongside an image of stars in the sky

A short history of medicine in the stars

How has medicine’s relationship with astronomy and astrology evolved over the last 900 years?

When you go to a doctor, you’d be pretty surprised if they turned to the skies to work out a diagnosis. But in the Middle Ages, medicine owed more to astrology than to biology – and according to the astrologer-physicians of the time, the phase of the Moon could have much more drastic implications than just affecting your chance of meeting a tall, dark stranger. Interpreting the stars was an essential diagnostic skill, while knowing your horoscope could be a matter of life and death.

Humours and elements

Astrological medicine was based on an understanding of humanity and our place in the universe, which was in turn based on medieval interpretations of classical ideas on the subject. Physicians believed that the human body was a microcosm of the wider world (the ‘macrocosm’).

The body therefore had a close relationship with its environment; for example, the four bodily ‘humours’ popularised by ancient Greek physician Galen (blood, phlegm, yellow bile and black bile) corresponded to the four elements making up the physical environment (earth, air, fire and water).

Based on this theory of the close relationship between the body and the universe, medieval physicians were able to use observable environmental phenomena – such as the movements of the stars – to explain the causes of disease, which remained obscure and unobservable.

Consulting the stars

Astrological ideas entered medical practice in Europe soon after ancient Arabic texts on the subject were translated into Latin in the 12th and 13th centuries. However, interpreting careful studies of the stars and applying the information to the treatment of disease was a complex task.

Many physicians carried almanacs to help them: these were handy fold-out, pocket-sized booklets containing carefully illustrated star charts, calendars and diagrams – all the information the physician would need to decide how to treat a patient. For example, bloodletting was a trusted therapy for common ailments such as headache, but it could be risky if undertaken at the wrong part of the astrological cycle.

According to the theory of melothesia, each body part was linked to a particular star sign; as the Moon moved through its different phases, the blood in the body would pool in the areas corresponding to the relevant star sign, making bloodletting from these body parts very dangerous. Therefore, to carry out the procedure safely, physicians would consult diagrams of the parts of the body and their associated star signs alongside astrological charts and calendars – all handily contained in their almanac – to work out when and where on the body it was safe to let blood.

Indeed, by the end of the 1500s it was the law in Europe that physicians had to consult the phase of the Moon before carrying out complex procedures such as surgery or bloodletting.

Keeping records

We can also learn much about astrological medicine from casebooks kept by astrologers. These provide a daily record of patients, consultations, and treatments administered. A recent project led by historians of science at the University of Cambridge has studied the casebooks of two 16th-century astrologers. These meticulous records reveal the breadth of ailments, problems and questions the physicians were called on to cure or solve by interpreting the stars: from cases of “measells” and “the pox” to questions about pregnancy, marriage, and even the likelihood of a shipwreck and whether to pay taxes.

Still looking to the stars?

Browse records like these, with their star charts and references to treatments such as “electuary of roses”, and the world of astrological physicians could hardly seem more alien to modern medicine. However, the relationship between the stars and medicine persists today, sometimes in unexpected ways.

Some people support the idea that astrology should still be used as part of medicine. British MP David Tredinnick claimed in 2015 that astrology could help save the NHS, supporting his argument with a quotation from the Greek physician Hippocrates: “A physician without knowledge of astrology has no right to call himself a physician.” Although Tredinnick’s proposal attracted considerable attention in the press, this is rather a minority opinion.

On the other hand, astronomy (rather than astrology) has led to new ways to detect and image cancers by applying the principles of imaging very large, very distant objects to understanding microscopic cells. The medical scanners we use today – MRI, CT/CAT and PET scanners – were developed using technology called aperture synthesis, an astronomy technique developed by Nobel Prize winner Martin Ryle in the mid-20th century.

Astronomical science and space-age technology have found their way into many other aspects of modern medicine, from air filters to ensure ultra-clean environments in hospitals and laboratories as well as spacecraft to thermal sensors for controlling the heating in neonatal units.

We might no longer need to consult a star chart when we visit the doctor, but the ancient relationship between space and medicine continues in fascinating ways.

Lead image:

Microscope image of a nervous system tumour alongside an image of stars in the sky.

Left: CNRI/Science Photo Library; right: Rogelio Bernal Andreo (DeepSkyColors.com)


Questions for discussion

  • When did medieval understandings of the body change, and what ideas replaced them?
  • Ancient Greek physician Galen promoted many long-standing theories about the body – the four humours are mentioned above. What other theories did he have about how the body works?
  • This article focuses on astrological medicine in Europe during the medieval period. Find out about the history of medicine in other parts of the world (try China, India and the Arab world) – did they also use the stars to study and practise medicine?

Further reading

Downloadable resources

About this resource

This resource was first published in ‘Space Biology’ in June 2015.

History, Health, infection and disease
Space Biology
Education levels:
16–19, Continuing professional development