The Star of the Magi

Courtney Roberts, M.A.

Tycho, Kepler & Galileo:  Astrologers in the Service of Science

From ‘Bruno at the Stake? Astrology, Science, and Academia’ by Courtney Roberts, M.A.

It has often been alleged that astrology and astrologers were put out of business by the discoveries of the Copernican revolution. In fact, astrologers were enthusiastic promoters and educators, putting the powerful public forum of their annual almanacs into the full service of science.

More to the point, the most important astronomers of the time were also practicing astrologers. The historians of science, in celebrating the glories of science past, have been accused of being less than forthcoming about this. 

Tycho Brahe, whose discovery of the “New Star” in 1572 caused a sensation when it shattered the Aristotelian theory of the immutability of the celestial spheres, was at the time of the discovery, working as astrologer to the Danish court.

While Tycho is lauded in science history for his painstakingly accurate observations, the fact that Tycho originally undertook these observations both to improve the accuracy of his horoscopy and to demonstrate the celestial harmonies underlying astrology, alchemy, and medicine, is conveniently overlooked.1           

                       Some would say it was deliberately suppressed. 


                                       Kepler's Platonic Solid model of the Solar System

from Mysterium Cosmographicum (1600)

             Tycho Brahe - The Imperial Astrologer                  

Tycho was a competent astrologer who made some surprisingly accurate forecasts for the Danish monarchy. He was also equally interested in alchemy, particularly the medical alchemy of Paracelsus.  While two of his early tracts, Against Astrologers, For Astrology, and another on new methods of house division, have since disappeared, other works have survived. For instance, in 1574, lecturing in Copenhagen, Tycho elaborated on his theories about the astrological correspondences between the heavenly bodies, terrestrial substances (metals and stones) and the organs of the body.2 

Tycho not only wrote astrological interpretations of both his ‘New Star,’ (the supernova of 1572) and the comet of 1577, he also did extensive work in astrological weather prediction.  Some of his basic principles of astro-meteorology were published in 1573 in De Nova Stella, but his work in this direction continued throughout his life and he left behind copious notebooks and personal accounts. 

In 1599, Tycho resettled in Prague, taking the post as Imperial Mathematician, (which meant ‘astrologer’) to the Holy Roman Emperor, Rudolf II, whom he provided with horoscopes and predictions.  When he died two years later, the successor to his position as Emperor Rudolph’s astrologer was his assistant, Johannes Kepler.



Portrait of Tycho Brahe now hanging in the Bodleian Library. The portrait belonged to Flamsteed and came to the University in 1752 as the gift of James Hodgson F. R. S.






            Johannes Kepler - The Lutheran Astrologer           

Kepler was a deeply religious man who had originally aspired to become a Lutheran minister.  Like Phillip Melanchthon, his astrology was part and parcel of his Christianity. 

As the Imperial Mathematician, he not only interpreted horoscopes for the emperor and his court, he published regular almanacs and predictions and made himself available for questioning on astrological and meteorological matters by the people of Prague, about which he complained, “…those of the lower classes with straight-forward and active minds…I get such a working over that I might as well call them my teachers.”3

Kepler’s biographer Caspar relates an incident which occurred as a series of sextile aspects were shaping up in the heavens:

“Kepler swore 15 days before, in front of doubters, that there would be wind and rain on that day.  In due course, on the day in question, came a fierce gale, driving black clouds, so that at noon it was as dark as half an hour before sunset.  Amazed, the people asked themselves what was happening.                      

Then the cry grew loud, ‘Kepler comes’.”4

                   Military Astrologer & Reformer                        

In the course of his work for the Imperial Court, as ‘district mathematician and calendar maker’ in Graz, and later as astrologer for the famous General Wallenstein, Kepler made some interesting and accurate predictions that have been preserved in his publications and biographies. For instance, in 1595, he predicted a peasant uprising, an invasion by the Turks, and an especially cold winter, all of which came to pass and bolstered his reputation.5  

His calendar for 1618 said that ‘if a true comet should appear in the heavens’ then the other calendar writers would have to ‘sharpen up their pens.’6

Three comets in all appeared that year, including one with a spectacularly bright tail.

Kepler also published extensively on his passion for reforming astrology: something of a hot topic in his time.  His astrological works have only just recently been translated into English – again, some would say, they were deliberately suppressed.  Even today, many English-speaking astronomers and physicists will adamantly deny that Kepler had any genuine interest in  astrology.  

          The Harmony of the Spheres             

In 1601 Kepler published De Fundamentis Astrologiae Certioribus, or, On the More Certain Fundamentals of Astrology, in which he explains his opinions on how, and to what extent, astrology works.

In 1610, He published Tertium Intervens, or the Third Man in the Middle.  In this classic of astrological reform, he presents himself between the two extremes of those who practice superstitious star-gazing and those who want to throw astrology out altogether. 

In 1619 he published his masterpiece, Harmonices Mundi, which was also not translated into English.  Kepler poured twenty years of his life’s work into this grand synthesis of geometry, arithmetic, music, astrology and astronomy, which also contained his third law of planetary motion.

eometrical harmonies in the perfect solids from Harmonices Mundi (1619) 


Astrology was not something that Kepler did merely to make money, as has often been claimed.  He cared deeply about it and he saw the universe through his own uniquely Pythagorean, harmonic paradigm. He was, as he described himself to his mentor, Michael Maestlin,  a 'Lutheran astrologer'.  

Kepler was not, as later biographers have styled him, a radical rationalist out to make the world safe for science by ridding it of medieval superstition: and neither were his contemporaries. It was because of his passion for astrology, and not in spite of it, that he made the discoveries that brought him lasting fame as one of the greatest astronomers of all time.

The quote below reveals just how personal Kepler’s astrology was.  In a letter to Johan Herwart from 1599, he discusses his own horoscope:

"In my case, Saturn and the sun work together in the sextile aspect (I prefer to speak of what I know best).  Therefore my body is dry and knotty, and not tall.  My soul is faint-hearted and hides itself in literary corners; it is distrustful and fearful; it seeks its way through harsh brambles and becomes entangled in them.  Its habits are similar.  To gnaw bones, to eat dry bread, to taste spiced and bitter things is a joy to me.  To walk over rugged paths, uphill and through thickets, is a holiday treat for me.  I know no other way of seasoning my life than science; I do not desire any other spice and I reject it if it is offered to me.  My fate is precisely similar to this attitude.”7

           Galileo - Court Astrologer to the Medicis                 

Kepler liked to correspond, and one of his more famous correspondents was Galileo, with whom he communicated on matters both astronomical and astrological.  Until quite recently, it has been difficult to find any English language references to Galileo’s astrology, (again, some would say they were deliberately suppressed) but  Galileo did both practice and teach astrology throughout his life. 
Galileo stayed very busy with his consulting clientele, which included the Medici family.  In 1610, Cosimo II appointed him to the post of court mathematician and philosopher (astrologer).
Galileo’s Astrologica Nonulla, contains fifty pages of horoscopes, along with his notes and interpretations, which lend insight into the personal idiosyncrasies of his art. 

On the other hand, Issac Newton, in spite of all claims to the contrary, seems to have had no specific interest in astrology.  He was, however, preoccupied with a consuming passion for alchemy and eschatological biblical exegesis, both of which involved a significant amount of astral determinism and planetary influence.  

Curry, in quoting Simon Shaffer, reveals that 

“Newton believed that in addition to replenishing the vitality of the cosmos, the sacred power of comets extended to sweeping away all idolatrous corruption on the Earth, including ‘astrologers, augurs, aurispicers…(and) such as pretend to ye art of divining.’” 8

 Now that is the very height of irony; that the astrological influence of comets was believed, by so great a man, to be sufficiently sacred to sweep away the idolatrous outrages of the astrologers themselves!    

If only it were that easy...

 End Notes                                                                          
1. Campion. N.,‘The Astronomical Revolution’(unpublished paper)

2. Mosley, A., ‘Tycho Brahe and Astrology’ at,

3. Kitson, A., Ed., History and Astrology: Clio and Urania Confer, London, Unwin, 1989, pg. 162

4. Caspar, M., Kepler, English Translation, Collier-Mac, 1962, pg. 172, quoted in History and Astrology, pg. 170

5. Kusukawa, S., ‘Kepler and Astrology”’ at, accessed on Jan. 7, 2004       

6.Kitson, A., Ed., History and Astrology: Clio and Urania Confer, London, Unwin, 1989, pg. 162

7. Kitson, A., Editor, History and Astrology: Clio and Urania Confer, London, Unwin, 1989, pg. 152

8. Curry, P., ‘Astrology in early modern England: the making of a vulgar knowledge’ in S. Pumfrey, P.L. Rossi, and M. Slawinski (eds.) Science, culture and popular belief in Renaissance Europe, pg. 283.  Curry cites Newton quoted from Schaffer, ‘Newton’s comets and the transformation of astrology’ in Curry, ed. Astrology, cit. (n. 14) pp. 242-3



The Star of the Magi

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