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Tertium Intervens - 'Third Man In The Middle'
De Fundamentis
A Composer of Calendars
Two Notable Correspondents
Throwing Out the Zodiac?
Harmonices Mundi
Notes & References
About the Author

Kepler & the Music of the Spheres by David Plant


Kepler's Belief in Astrology by Nick Kollerstom

'The soul of the newly born baby is marked for life by the pattern of the stars at the moment it comes into the world, unconsciously remembers it, and remains sensitive to the return of configurations of a similar kind.'
Kepler, Harmonics Mundi, chapter 7

Kepler's lifelong attempt to recast astrology within a harmonic-Pythagorean framework has relevance today. The year 1987 saw the first visible supernova since Kepler's star of 1604.[1] At the quatercentenary of his De Stella Nova of 1606 about the new star and his theories of how astrology worked, this seems an appropriate time to re-examine the achievement.

Very few of Kepler's astrological works have been translated into English down the centuries, which has permitted a radically one-sided interpretation of his work to flourish. In recent years, however, modern translations of one of Kepler's seminal works on the theory of how astrology works have appeared,[2] which have been made available for the first time to English readers a perspective on what he really believed. That one of the great creative founders of modern science struggled for decades to relate together astronomy and astrology is a matter of no small importance.

Was it indeed the case, as one scornful academic has argued, that "Kepler's remedy [that is, his proposed reform of astrology] was one of those that in the end kill the patient"?[3] Historians seem agreed that Kepler's beliefs have had small effect upon posterity, being against the tide of events.

Kepler's defence of astrology. . .seems to have been entirely without effect upon later generations. [4]

Another expressed the view that Kepler's rationalizations of the subject

could not endure nor gratify in an age of expanding experimentation … proved very shaky supports and were worth no more than straws to drowning men. They stopped with Kepler or with men like Fludd. With the passing of that generation they are never heard of again.[5]

Like Ptolemy, Kepler regarded the twin themes of astronomy and astrology as being of equal interest and value - but he was the last of this tradition. He was, quite simply, the last Western astronomer of note to believe in astrology.[6] After him the abyss opened up, which he would surely have regarded as a more terrible thing than the religious disputes of his day. He was employed as a 'mathematicus', a term related to astrology and astronomy as well as mathematics, which did not have the abstract meaning of today. As Kepler is known to all astronomers for the three laws of planetary motion he discovered, so is he today known among astrologers for the three new aspects he formulated.

In his presidential address to the British Astronomical Association in 1979, Leslie White said of Kepler that it was not generally appreciated that "throughout his troubled life until his death in 1630, his inspiration and his most magnificent ideas came directly from Pythagorean cosmology".[7] These beliefs of his are normally dismissed in the history books as mere vestiges of a medievalism from which he was regrettably unable to free himself - in striking contrast to his more modern contemporary, Galilieo. In 1601 Kepler wrote De Fundementis Astrologiae Certioribus, and then in 1619, Harmonics Mundi. The former is of especial interest to us, as being in the form of an extended introduction to his yearly almanac, written in Latin and somewhat a bid for the post of imperial mathematician at Prague - in which he was successful. It gives, as he says, "what one may state and defend on physical grounds concerning the foundations of Astrology and the coming year 1602". The latter opus, which took twenty years to compose, was a grand five-point synthesis of geometry, arithmetic, music, astrology and astronomy. Its recent translation into English gives us a basis, at last, for a complete picture of his work - even though it tends to be remembered today merely because of the third law of planetary motion contained in it.

Tertium Intervens - 'Third Man In The Middle'

In 1610 he published his Tertium Intervens or 'Third Man in the Middle', wherein he defined his position over the gathering storm of controversy between astrology and astronomy.[8] The title page referenced to "Star-gazing superstition", but also warned "theologians, physicians and philosophers against throwing out the baby with the bathwater, and thereby maltreating their profession".[9] They would be, he claimed, maltreating the profession if they threw out astrology, or rather the kernel of truth which he believed that it held. (NB, that seems to be the first use of the phrase about babies and bathwater.)

At this time he was the imperial mathematician under the Emperor Rudolf II at Prague. He had risen to the post after the death of the astronomer, Tycho Brahe, in 1601. Previously he had worked in Graz, Austria, teaching secondary school mathematics. It was there that he commenced preparing yearly almanacs and cast horoscopes. In 1595 an odd notion came to him. To quote Carl Sagan's account, slightly dramatized from contemporary evidence:

Kepler was a brilliant thinker and a lucid writer, but he was a disaster as a classroom teacher. He mumbled. He digressed. He was at times utterly incomprehensible. He drew only a handful of students his first year at Graz; the next year there were none. He was distracted by an incessant interior clamour of associations and speculations vying for his attention. And one pleasant summer afternoon, deep in the interstices of one of his interminable lectures, he was visited by a revelation that was to alter radically the future of astronomy. Perhaps he stopped in mid-sentence. His inattentive students, longing for the end of the day, took little notice, I suspect, of the historic moment.[10]

The strange notion which then dawned upon Kepler was the idea that the five Platonic solids, nesting one inside the other, could specify the relative distances of the six planets on their orbits round the sun. (He was by this time committed to the Copernican, sun-centred universe.) Only one person had astronomical observations accurate enough to test this model, and that was Tycho Brahe; and, to quote Sagan again, "by chance, at Rudolf's suggestion, he [that is Brahe] had just invited Kepler, whose mathematical fame was growing, to join him in Prague". This belief meant a lot to him, even though his later discovery of elliptical orbits was somewhat to diminish its credibility.

The two of them must have had some interesting conversations together. It was the view of Tycho Brahe that: "Those who deny the influence of the planets violate its clear proofs, which it does not become people of sound judgement to contradict".[11] In the vast transition from the closed Ptolemaic world to the infinite Copernican universe, the two shared the conviction that, though many traditional beliefs would have to be jettisoned, the fact of celestial influence could be demonstrated. As Kepler inscribed on the title-page of De Fundamentis, (1601) "Discover the force of the heavens O Men: once recognised it can be put to use".

De Fundamentis

This work, whose title can be translated as 'On Giving Astrology Sounder Foundations,' or 'On the more Certain Fundamentals of astrology', gives quite concisely Kepler's view of how and to what extent astrology works; in a manner which may not yet have been improved upon. It was a foreword to his yearly almanac, written in Latin because it comprised his bid for the post of Imperial Mathematician. As regards what one ought to say in a prognostic (pro-gnosis, i.e, knowledge-in-advance), he warned:

For he who will please the crowd and for the sake of the most ephemeral renown will either proclaim those things which nature does not display or even will publish genuine miracles of nature without regard to deeper causes is a spiritually corrupt person… With the best of intentions I publicly speak to the crowd (which is eager for things new) on the subject of what is to come.

- possibly with undue optimism, he invited his patron to compare his forecasts with political events, "For only those who are concerned the success of these forecasts".

His early work had attempted to explain aspects by relating them to three-dimensional solids but this didn't really get very far. His later work derives more completely from musical intervals. He explains the five aspects Ptolemy used and the three new ones of his own by taking various fractional lengths of a string, as with violin string, and looking at which rations give pleasing harmonics and which do not; but even this doesn't work perfectly and he spends a lot of time looking at two-dimensional plane figures and their degrees of symmetry. As a mathematician, he discovers a couple of new such combinations - 'tessellations' or regular figures that lock into each other on a plane surface, and he uses the angles which they form to explain which harmonics are astrologically important and which are not. So, there are a lot of diagrams in his work showing regular figures in terms of the angle made against the zodiac. He asserted that "No more than 8 harmonic ratios arise from comparing the regular plane figures", adding that he hoped one day to be able to demonstrate this. These give him the eight aspects of conjunction, opposition (1:1), trine (1:2), square (1:3), quintile (1:4), biquintile (2:3), sextile (1:5) and sesquiquadrate (5:8). So there is a big difference between Kepler's approach to harmonics and that which the late John Addey developed:[12] Kepler seeks to show there are only a limited number of aspects that actually work in astrological terms.[13]

Concerning the three new aspects which he discovered - the quintile (72 degrees), the biquintile (144 degrees) and the sesquiquadrate (135 degrees) - he claims to have detected their effect through years of weather observations. Their effect was a matter of empirical enquiry as much as anything else in the natural world; in this view he differs radically from other founders of modern science in the seventeenth century. He had a collection of 800 horoscopes,[14] and claimed also to have taken daily weather observations over a period of some sixteen years.

De Fundamentis describes the effects of the sun and moon and the planets in terms of their light, the influences of the moon upon humours etc, and then comes on to his view that "Earth has a vegetative animal force, having some sense of geometry". The earth is stimulated by the geometric convergence of rays formed round it; the world-soul is sentient but not conscious. As a shepherd is pleased by the piping of a flute without understanding the theory of musical harmony, so likewise earth responds to the angles and aspects made by the heavens but not in a conscious manner. Eclipses, he says

are so important as omens because the animal faculty of the Earth is violently disturbed by the sudden intermission of light, experiencing something like emotion and persisting in it for some time.

He surmises that there are "cyclic journeys in the humours of the Earth", and gives an example "the 19 year period of the Moon" which sailors say affects tides - presumably the 18.6-year nutation cycle, that is rotation of the lunar nodes - and "if this is so the laws and periods of the cycles should be investigated by collating observations made over many years, something which has not yet been done". In recent years it has indeed been shown how climate effects, harvests and tidal heights do vary with such a nineteen-year cycle.[15]

Astrologers will be relieved to hear Kepler's views that, "If astrological predictions about a particular year prove mistaken I think they should be treated with indulgence, such is out ignorance of causes". In February (of 1601), Venus conjunct Mercury "will bring turmoil to the conditions of the atmosphere. Their influences are about as contradictory as those of Saturn and Mars". Then in March, "there will be thunder due to Sun opposing Mars, although Mars' latitude detracts from the force of this aspect", yet "The clustering of aspects adds force to it, thus there will be unnatural warmth". In April, "there will be rain at least two days before and after the Full Moon, since the planets are all aspected to one another". Because of Saturn and Mars at quintile in May, "There follows the most delightful mildness with moisture". That may be the first account of the effect of a quintile! Jupiter and Mars come together in July and "This will give clear skies and great heat".

Lunar aspects come and go too quickly to create weather, he explains; however body humours are affected by them:

let the physician, if he can, refrain from treating a seriously weakened patient when the Moon is in a powerful aspect. For every aspect is of itself a natural purgation. But if strong purges are needed let him on the contrary chose powerful aspects. Indeed, the whole business of crises depends upon the return of the Moon and its configurations with the planets, and it is vain to seek explanation for it elsewhere.

This view is of interest in view of the modern finding that hospital operations conducted during the full moon period are associated with increased amounts of bleeding.[16]

The last, political section of this 1601 calendar contains an affirmation on transits:

…almost every motion of the body or soul or its transition to a new state occurs at a moment when the figure of the heavens corresponds to its birth figure ...[17]

This comment is a propos the Jupiter-Mars conjunction coming up, where he says it would be usual for astrologers to predict the death of some outstanding military leader. Not wishing to "slander the heavens by asserting that they have been framed so as to kill men", he explains that "this movement leads to disaster for those who are ill disposed, but in the same way it draws on to great things those who are stronger by reason of their age or state of health. We may see each of these alternatives this year, but there is no necessity for them to occur".

For the Mars-Saturn conjunction in September, he recommends that, if "there is a risk of civil discord, let there be no assemblies in August and September - let them be dispersed, by an early removal of the causes of discontent, or let some new matter be proposed..." On the other hand, if a bold deed is to be undertaken, which "requires persevering effort", this time would be suitable, adding: "For it lies in our power to affect how these things turn out; it is not a matter of complete necessity". In the next paragraph he adds that this conjunction occurs "when these planets are rising over Poland" (?), and since there is already war in those parts, I think that these are signs of disaster for that region". I haven't managed to check up on this prediction. He concludes, "If, meanwhile, a secure peace is established, there will be absolutely no danger from the effects of the heavens alone".

A Composer of Calendars

Kepler went on producing calendars for three decades, from 1595 to 1624. In the city of Graz he worked as "district mathematician and calendar maker" and gained his initial renown from the accuracy of his first predictions: he predicted a winter of severe cold and an invasion by the Turks, both which came to pass. The composing of calendars was a traditional occupation for a mathematicus, and yet he feared lest it should compromise his scientific reputation, writing to Maestlin that "There is much therein which must be deliberately pardoned, or else it injures my reputation with you". His prognostications were expected to include such things as war and pestilence, weather and harvest, the religious and political upheavals, and when to sow or bleed or purge and the like. "Many of the rules of this Arabic art amount to nothing", Kepler said (to Maestlin). He only printed some 500 copies per year. Kepler's biographer, Caspar, referred to the calendar makers, "of whom there were very many"; it was a practice with much demand.

Of especial interest would be English translations of Kepler's prognosticums for 1603 and 1604. In 1603 many such works were printed about the Jupiter-Saturn conjunction of that year: this event, which occurs every twenty years, had just moved into a fire sign of the zodiac. This conjunction recurs in one element of the zodiac for ten consecutive conjunctions, i.e. two centuries, so what could this entry into a new element portend? Previously the transition of this conjunction-sequence into the fire-element had been seen as portending to the rise of Charlemagne, and before that it was in the time of Christ. What of note could be about to happen? This always seems to me to be the one instance where he does take seriously the zodiac.

Yet more awesome was the appearance the very next year of a new star, extremely bright, in fact sparkling and rainbow hued, right next to the Jupiter-Saturn conjunction, when it was also conjunct Mars! The four stars glittered in the constellation Ophiucus the Serpent bearer, and the imperial mathematician was asked to interpret it.[18] He was more interested in scientific observation of the new star, but everyone wanted to hear about what it signified. His 1604 work De Stella Nova, gives a discourse on signs and their interpretation,[19] but he there appears far from convinced as to what meaning could be assigned the spectacle.

The new supernova came to be called 'Kepler's star' though he had not discovered it. It is noteworthy that the only two 'new stars' ever seen in the West - that is supernovae or stars exploding within the Milky Way galaxy and therefore visible to the naked eye - are named after Tycho Brahe and Kepler.[20] One earlier one may have been seen in the time of Hipparchus, but there are no others. These two astronomers spent twenty tempestuous months together. The most accurate astronomical data ever made became accessible to the one person capable of interpreting them. Brahe found the situation very trying because his world system had an unmoving earth and Kepler would never accept this. It is easily forgotten that at the turn of the seventeenth century Brahe's system, where the earth rotated daily but otherwise did not move, was more widely accepted than either the Ptolemaic or the Copernican systems. It was a pragmatic compromise. Brahe was handing his data over to a man who was going to demolish the credibility of his world system, and instead enthrone the Sun at the centre of things. He needed Brahe's data to do this. However, the two maintained a deep mutual respect.

Kepler as the imperial mathematician found himself on occasion grilled by the people of Prague over his astrological views and weather prophecies. From "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", he noted. One on occasion his biographer Casper tells how, when a few sextile aspects were in prospect:

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 dark as half an hour before sunset. Amazed, the people asked themselves what was happening. Then the cry grew loud, 'Kepler comes'.[21]

His 1618 'prognostication' predicted that the month of May would "bring great upheavals to the world", and in that historic month two Prague councillors were thrown from a window and the thirty Years' War broke out. The 1618 calendar contained the remark that "if a true comet should appear in the heavens' then the calendar writers would have to sharpen their pens". In that year, no fewer than three comets made their appearance, one having an especially bright tail. It was evident to all that this was an omen concerning the war that had broken out, as the emperor confronted the rebellious Bohemians, but of what kind? People waited to hear whom Kepler would side with, whether, as he put it, he was 'fox or hare'. After all, he was a staunch Protestant in a Catholic court and this was a religious war. It was for just this reason that he disapproved of making predications, as it appealed to superstition in a way that enabled people to be manipulated. His belief in comets as omens seems to have been as follows: though such belief in omens was superstition, the Deity had some regard for popular superstition and so could arrange for comets to appear in the appropriate places and times to have a suitable message.

On the subject of making predictions, we may note that when the renowned General Wallenstein anonymously requested his horoscope, Kepler appended to the horoscope the words: "I have only devised horoscopes when I was sure that my work is intended for somebody who understands philosophy, and is not afflicted with contradictory superstition". (He apparently understood that it was intended for Wallenstein.) To be sure, Kepler was criticized when Wallenstein was killed on 25 March 1634: on being asked for some future prediction in 1624 by Wallenstein he did give them, but they ended with the date of March 1634, which he said, "will entail a terrible confusion in the country which will affect him". The dire question was asked, had this prediction been self fulfilling, as the general had always been so dependent on astrologers?[22]

Two Notable Correspondents

One of Kepler's regular correspondents, the physician Georg Brengger, noted in a letter to Kepler in 1608:

You say you have confirmed by meteorological experience that there exist the additional aspects quintile, biquintile and sesquiquadrate. I myself should like to see an example of this observational material, for with a number and variety of aspects always occurring, so that one is unsure to which of them one should ascribe a change in the atmosphere, I do not know how I should make an observational test, or even whether I should find it possible to do so.

To this Kepler replied:

In 1600, when from 23 April until 2 May, New Style, there were no primary aspects, and Magini's tables showed Saturn and Jupiter to be at quintile, on 1 May there was a very heavy fall of snow both in Prague and in Styria for Ferdinand's wedding, and the jousting had to be cancelled. From observing the heavens, it was found that during these same days Saturn and Jupiter were 72 degrees apart. Tycho's students made the check on my behalf with Tycho's quadrant.

The majority opinion today would assuredly be in favour of Kepler's correspondent's view.

Kepler's correspondence with Robert Fludd does not touch on astrology directly, yet remains of a general interest concerning the nature of symbolism; it shows a disagreement between Fludd's pictorial-cum-occult view and Kepler's mathematical-cum-rational position. They had both composed treatises on the subject of Harmonices Mundi but from different viewpoints. Fludd, a Hermetic-cabbalist and London apothecary, averred that "Kepler is concerned with the external movement of things, but I with the internal and essential processes of Nature"; while Kepler maintained that Fludd's Hermetic analogies were "dragged in by the hair", adding that "Without mathematic demonstrations I am like a blind man". This correspondence was discussed by the physicist Wolfgang Pauli.[23]

Throwing Out the Zodiac?

Inasmuch as the soul bears within itself the idea of the zodiac, or rather of its centre, it also feels which planet stands at which time under which degree of the zodiac, and measures the angles of the rays that meet on the earth; but inasmuch as it receives from the irradiation of the Divine essence the geometrical figures of the circle and (by comparing the circle with certain parts of it) the archetypal harmonics (not, to be sure, in purely geometrical form but as it were overlaid or rather completely saturated with a filtrate of glittering radiations), it also recognises the measurements of the angles and judges some as congruent or harmonious, others as incongruent. [24]

That statement occurs in his great work, Harmonices Mundi, and shows a somewhat Platonic attitude, whereby the soul has a pre-existent concordance with the geometry of the heavens, so that it can in some way sense the impressions which it makes.

What were Kepler's grounds for dismissing the zodiac? For example, were they based on the problem of precession, whereby the zodiac divisions have moved away from their original stellar references? Forthcoming English translations of his works will, one hopes, throw some light on this matter. Mathematically he viewed the number twelve as the most perfect number for dividing up the circle. He may have found the triplicities of the zodiac more acceptable than the individual signs, as shown by his discussion of the Saturn-Jupiter 'great conjunctions' moving through the different elements.

It is certainly true that Kepler sometimes dismissed the zodiac; indeed he only reached the new aspects because of this attitude. While for Ptolemy, the five kinds of aspect were all formed between zodiac signs, that is they had to be multiples of 30 degrees, Kepler was prepared to ignore this limitation and thereby develop his new aspects. In 1606 Kepler wrote to an English scientist (Harriot) saying. "Ten years ago I rejected the division into 12 equal parts, the houses, the dominations [i.e., rulerships], the triplicities etc, all of that, keeping only the aspects and transferring astrology to the science of harmonics".[25] He rejected much of the traditional astrology in his attempt to recast it in a heliocentric world. For example, in a mood to oppose astrological determinism, he boasted that "An astrologer will search in vain in my horoscope for the reasons why in 1585 I discovered the relationship between the heavenly spheres", etc. But, on the other hand he wrote to a friend: "Regard this as certain, Mars never crosses my path without involving me in disputes and putting me myself in a quarrelsome mood" (to Fabricius in 1602). Should we conclude from this that he was prepared to blame the heavens for his temper, but not to allow it credit for his discoveries?

Figure De Trigono Igneo. this figure from De Stella Nova shows a sequence of Jupiter-Saturn conjunctions, which occur every twenty years, from 1603 to 1763. It shows the process of entering the three fire signs, and how this had fully occurred from 1663 onwards. Great predictions were made on the basis of this, which happens only every 800 years. It had happened previously, Kepler pointed out, at the time of Christ. Tycho Brahe had expressed the view that this was the seventh since the world began, and so it was a special epoch. Note the zodiac images Kepler has drawn around the sides.

Harmonices Mundi

Now because 18 months ago the first dawn, 3 months ago broad daylight but a very few days ago the full sun of the most highly remarkable spectacle has risen - nothing holds me back. I can give myself up to the sacred frenzy, I can have the insolence to make a full confession to mortal men that I have stolen the golden vessel of the Egyptians to make from them a tabernacle for my God far from the confines of the land of Egypt. If you forgive me I shall rejoice; if you are angry, I shall bear it; I am indeed casting the die and writing the book, either for my contemporaries or for posterity to read, it matters not which: let the book await its reader for a hundred years; God himself has waited six thousand years for his work to be seen.

This exclamation (in Harmonices Mundi, Book V) is normally viewed as Kepler rejoicing over discovering his third law, that the cube of planetary orbit radius is proportional to the square of orbit period - though with some puzzlement that the mere discovery of a mathematical law should get him into such a state. However, a modern scholar has pointed out that

the cause (for his rejoicing) is in the success of the harmonical archetype, which now, thanks to the period-radius law, can give a full account of the observed structure of the planetary system ... Kepler seems to be proclaiming his own success in the task at which Ptolemy failed, namely to give a true account of the harmony of the world, expressed in musical consonances, astrological aspects and the motions of the planets. Astrological harmony is an integral part of Kepler's work as it is of Ptolemy's.[26]

He discovered Ptolemy's Harmonica in 1617, saying that it afforded him an "especial increase of his passionate desire for knowledge and encouragement of his purpose" - so perhaps the "golden vessels of the Egyptians" referred to Ptolemy's studies in Alexandria. The apprehension that his endeavour might have to wait some time for readers who could understand it may have been justified.

But now, Urania, there is need for a louder sound while I climb along the harmonic scale of the celestial movements to higher things where the true archetype of the fabric of the world is kept hidden.

This seems a suitable position in which to leave Johannes Kepler, as he articulated the polyphonic song of the solar system in Book V of Harmonices Mundi. He expressed the hope that it would inspire musicians and one wonders whether it did so. For example, Venus and earth in their periods expressed the ratio 5:8 which as a musical sixth he saw as quite a pleasant ratio. (From the five inferior conjunctions of Venus every eight years). "The agreement is frighteningly good" was the verdict of the astronomer, Fred Hoyle, concerning the tie up between musical ratios and planetary velocities as Kepler described it, and he added:

One wonders how many modern scientists faced by a similar situation in their work would fail to be impressed by such remarkable numerical coincidences... [27]

While astrology is by its nature earth-centred, the music of the solar system was for Kepler heard more from the sun, because the relative speeds for the planets - between aphelion and perihelion, their points nearest to and furthest from the sun--interweave to give the consonant, that is harmonious sounding intervals. Britain's Kepler-expert J.V. Field has observed that Kepler's "elaborate polyphony turns out to be in excellent agreement with observation", and that there had been "no advance upon Kepler's explanation of how the system originally came by its resonances".[28]


Leibniz referred to Kepler as "that incomparable man", whom "the angels had watched over that he might be the first among mortals to publish the laws of the heavens, the truth of things, and the principles of the gods".[29] However, the mechanical philosophy which developed in the seventeenth century was opposed to his way of thinking. It took his three laws of planetary motion, it used his ephemerides tables, which were more accurate than any previously published by "nearly two orders of magnitude" [30] - and forgot the rest. The consequence was that, to quote the science historian Bernard Cohen, writing in 1975:

At the present time, not a single one of Kepler's greatest works has ever been completely translated into English, French, Russian, or Italian. And only on recent years have any of Kepler's writings whatsoever been published in complete English versions.[31]

Only his science fiction work, Somnium, about a journey to the moon, was translated and only one Kepler biography exists in English, by Max Caspar. Readers should note that some further translations of Kepler's work are planned for a special issue of the journal Culture and Cosmos journal[32] later this year.

This essay is an updated version of one printed in 'History and Astrology: Clio and Urania Confer,' 1989, Ed. A. Kitson.

Quotes from Kepler: and

Recent Publications on the subject: Two Renaissance Views of Astrology: Pico and Kepler, Sheila Rabin, 2003, UMI, Ann Arbour, Michigan.
Secrets of Nature: Astrology and Alchemy in Early modern Europe, Ed Neumann & Grafton MIT 2001, Ch. 4 by Darell Rutkin.
Soul-searching with Kepler: an analysis of "anima" in his astrology, Patrick Boner 'Journal for History of Astronomy' 2005, 36, 7-20.

Title page from Kepler's 'De Stella Nova' 1606

Title page from Kepler's 'De Stella Nova' 1606

Notes & References:
  1 ] Kepler's star of 1604 was a galactic supernova, that is an exploding star in our galaxy. The 1987 supernova was an explosion in a daughter galaxy to the milky way, one of the Magellanic clouds, visible in the southern hemisphere. Other supernovae in between these two were in other galaxies and so only visible telescopically.
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  2 ] The Harmony of the world (Harmonices Mundi 1618) translated by Eric Aiton, Andrew Duncan and Judith Field, 1997 Philadelpia.

Judith Field's, 'A Lutheran astrologer: Johannes Kepler', Archive for History of Exact Sciences, vol. 31,(1984) pp. 190-268, contains a translation of De Fundamentis entitled 'Johannes Kepler's On the More Certain Fundamentals of astrology'. A translation of this was also published by Bruce Brackenridge and Mary Rossi in Proceedings of the American Philosophical Association (1979).
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  3 ] G. Simon, 'Kepler's astrology: the direction of a reform', Vistas in Astronomy, vol. 18 (London: Pergamon, 1977), p. 446.
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  4 ] J.V. Field, 'Astrology in Kepler's cosmology', in Patrick Curry (ed.), Astrology, Science and Society (Boydell, 1987), p. 169
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  5 ] M. Grabaud, 'Astrology's demise', Osiris, vol. 13 (1958), p. 253.
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  6 ] But note also Galileo's routine practice of astrology. See and
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  7 ] L. White, 'Pythagoras', presidential address, Journal of the British Astronomical Association, vol. 90 (1980), p. 123.
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  8 ] A translation of this work by Ken Negus is, one gathers, nearly ready.
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  9 ] Max Caspar et al. (eds), Gesammelte Werke, vol. 4 (Munich, 1937), p. 147.
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  10 ] Carl Sagan, Cosmos (1980, 1983, p. 57.
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  11 ] Lecture by Brahe at the University of Copenhagen, 27 September 1574, Oratio de Disciplinis Mathematicus (quoted in Sven Svensson, Dynamic Astrology (Spearman, 1983), p. 12).
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  12 ] J. Addey, Harmonics in Astrology (Fowler, 1976).
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  13 ] The smallest aspect that could be effective Kepler ascertained by looking at polygons of decreasing 'nobility', that is degree of symmetry, and this he found reached a limit at 'configurations which hesitate between power and powerlessness, namely the 24 degree arc from the pentkaedecagon [fifteen-sided] and the 18 degree arc from the icosigon [twenty-sided]' (Harmonics Mundi, Book IV, proposition XV).

Field comments "The lowest grade of configurations which are definitely accepted as aspects is that of the decile [36 degrees], tridecile [108 degrees], octile [45 degrees] and trioctile [135 degrees] aspects" (op.cit., 1984, p. 218).
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  14 ] One hears this said, but its not clear where any of them are now. His astrological manuscripts were supposedly kept at the Pulkova archive in St Petersburg. The 20-volume Works contains virtually no Kepler horoscopes.
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  15 ] M. Gauquelin, The Cosmic Clocks (Owen, 1969), p. 103
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  16 ] E. Andrews, 'Moon talk, the cyclic periodicity of postoperative haemorrhage', Journal of the Florida Medical Association, May 1960, pp. 62-6
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  17 ] J. Kepler, De Fundamentalis, section LXXV, 1602
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  18 ] On 17 October 1604, when Kepler saw this new star, it stood at 22 degrees of Sagittarius, merely 3 degrees from the ecliptic, with Jupiter at 20 degrees, Mars at 25 degrees and Saturn at 12 degrees of the same sign.
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  19 ] Translation of parts of De Stella Nova are expected in the journal Culture and Cosmos in 2006.
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  20 ] 'Tycho's star' of 1572 was in a spiral arm at the edge of our galaxy, while 'Kepler's star' was a supernova near to its centre. The explosion of 1054 which formed the crab nebula would have been at least as bright and visible in daylight; however, no European records exist of its sighting, an indication of the prevalent belief that the heavens were immutable. Book II of Pliny's Natural History describes the new star seen by Hipparchus.
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  21 ] M. Caspar, Kepler, English translation (Collier-Mac, 1962), p. 172.
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  22 ] For a discussion see A. Beer, Vistas in Astronomy, vol. 18 (London: Pergamon, 1978), p. 408
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  23 ] W. Pauli. 'The influence of archetypal ideas on the scientific theories of Kepler', in C. Jung and W. Pauli, The Interpretation of Nature and the Psyche (London: Routledge, 1955). See also Brian Vickers (ed.), Occult and Scientific Mentalities in the Renaissance (Cambridge: CUP, 1986), ch. 3, p. 153, ch. 5, pp. 177-229 and ch. 8, pp. 284-90.
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  24 ] Harmonics Mundi, Book IV (quoted in W. Pauli, op. cit.).
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  25 ] Letter to Harriot, 1606 (quoted in Vickers, op. cit., p. 267).
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  26 ] J.V. Field, 'Astrology in Kepler's Cosmology' in P. Curry (ed.), Astrology, Science and Society (Boydell, 1987), p. 168.
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  27 ] Quoted in A. Beer, 'Kepler's astrology and mysticism', Vistas in Astronomy, vol. 18 (London: Pergamon, 1975), p. 408
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  28 ] J.V. Field, op. cit., p. 290.
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  29 ] G. Leibniz (1689), 'Essay on the causes of the motions of the heavenly bodies' in Acta Eruditorum, quoted in I. Bernard Cohen, 'Kepler's century', Vistas in Astronomy, vol. 18 (London: Pergamon, 1975), p.12.
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  30 ] O. Gingerich, 'Kepler's place in astronomy', Vistas in Astronomy, vol. 18 (London: Pergamon, 1975), p. 262: "The fantastic improvement of nearly two orders of magnitude in the prediction of planetary positions ..."
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  31 ] I. Bernard Cohen, op. cit., p. 5.
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  32 ] Watch for details.
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See more articles by Nick Kollerstrom

Nick KollerstromNick Kollerstrom has a Cambridge science degree and has worked as a physics schoolteacher. He is recognised throughout the astrological community for his pioneering studies that have brough his scientific background into exciting fields of research on planets, plants and metals. He has been actively involved in the study of planet-metal associations and other matters of a Hermatic nature for 30 years, and has lectured on these subjects since 1975. His work in medical research resulted in his book Lead on the Brain - a plain guide to Britain's No 1 pollutant. His investigation of lunar effects upon plant growth led in the 1980s to his gardener's guide Planting by the Moon and the popular annuals Gardening and Planting by the Moon. Nick Kollerstrom's latest title, Crop Circles: The Hidden Form, published by Wessex books, offers a new way of experiencing the crop circle mystery, through the geometry of the forms revealed in crops.

You can contact Nick by email at nk(at)

© Nick Kollerstom, 2006.

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