Talk:Johannes Kepler

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Archive 1 - through November 2006

Total re-write

I've re-written this article, mostly from scratch. Any feedback will be greatly appreciated; I would like to work this into a Featured Article.--ragesoss 06:59, 16 December 2006 (UTC)

Well done as its definitely better. I think it should be made clear that Kepler did believe in astrology. He not onlyed used it professionally but also privately e.g to help pick his wife. It was not commonsense that he used but genuine astrological methods and he was very lucky that he was surprisingly correct often. BernardZ 05:19, 18 December 2006 (UTC)

I think the article is pretty clear about him being an astrologer, though I agree that the ways in which he used astrology in his personal life are telling and could due for some elaboration.--ragesoss 05:22, 18 December 2006 (UTC)

I think you have edited a bit too much out. It was not just personal. Kepler sincerely believed in astrology, he had a good reputation as one and it was also a good source of income for him. For example in 1595 he predicted correctly bitter cold, a Turkish attack and a peasant uprising. These predictions certainly were not from common sense but luck. BernardZ

Logicus Criticisms

Unfortunately the article is fundamentally defective from the philosophy of science point of view, with its central interest in the logic of scientific discovery. And as the Wikipedia article on history of science used to tell us, the very rationale of the history of science is to provide a testbed for the theories of philosophy of science such as its theories of the rationale of theory change. But what it does not tell us is that history of science is itself already constructed and biassed according to various philosophies of science, and Ragesoss adopts standard mistaken inductivist and revolutionist philosophies of the standard mistaken positivist theory of a scientific revolution. Here I make just three major corrective points.

• Kepler's kinematical laws of planetary motion are most certainly not the foundation of Newton's gravity theory: As Duhem, Popper, Feyerabend and others have periodically pointed out, the planets do not move in ellipses and Kepler's laws are therefore false according to Newtonian dynamics. If they were true, then Newton's theory of mutual gravitational attraction and his planetary gravitational perturbation theory must be false. Newton's astro-dynamics and theory of gravity contradicted Kepler's and falsified his kinematical laws. In fact whilst writing the Principia Newton was greatly concerned with falsifying Kepler's Rudolphine Tables with such as the non-elliptical gravitationally perturbed motion of Saturn. In fact refuting the Rudolphine Tables based on Kepler's laws was something of a sport amongst English astro-physicists. Thus the opening claim that “Kepler's laws would be the foundation of Isaac Newton's theory of universal gravitation” must be deleted as illogical nonsense.

• Circular orbits were not replaced by ellipses: One of the sillier and scientifically ignorant positivist myths of a scientific revolution is that Kepler successfully replaced circular planetary orbits with elliptical ones, which was supposedly revolutionary. But on the one hand since Appollonian epicycles in antiquity, planetary orbits were not circular but were at most epitrochoid, as even the Wikipedia article on the epicycle points out, and planetary orbits were most certainly not thought to be circular immediately before Kepler's astronomy. And on the other hand planetary orbits are not elliptical according to Newton's dynamics. 'From circles to ellipses' is a total myth. Of course Galileo and Newton and others supposed planetary orbits to be circular or indeed elliptical as simplified models posited for specific theoretical purposes. But false kinematical assumptions made for hypothetical dynamical modelling purposes should not be confused with reality. Unfortunately the article has been influenced by this basic error. Thus such false claims as the following two and others must be deleted or corrected:

"Since antiquity, it was assumed a priori that the natural motion of planets was circular; retrograge motion was acccounted for, in Ptolemaic astronomy, through circular epicycles, ..."

"All earlier astronomers, including Copernicus, conceived of the planets as dense spots within a system of orbs, spherical shells that rotated to produced the observed motion of planets; a planet's distance from its center of rotation based on many points was assumed constant."

In general I presume it is an interesting unanswered question whether the orbital trajectories of the solar planets are best approximated on average by a circle, ovoid, epitrochoid, ellipse or any other closed curve, noting Newton's observation that in humanly scientifically unfathomable complex reality, they are not recurrent closed curves at all, since in dynamically complex reality no planet repeats its orbit.

• Kepler's major historical achievement lay in producing a scientifically progressive Aristotelian inertial astro-dynamics: Kepler's astro-dynamics from his Astronomia Nova onwards explodes the standard positivist narrative of an astro-dynamical revolution according to which a heliocentric revolution in kinematical astronomy precipitated an anti-Aristotelian revolution in dynamics because a moving earth necessitated an 'anti-Aristotelian' dynamics in which such motion does not require an external mover. But this narrative is obviously logical nonsense inasmuch as there is no logical reason why heliocentrism cannot be associated with a dynamics that requires external movers for such motion, and indeed it was. For both Copernicus and Kepler posited external movers of the planets - Copernicus posited the planets were moved by rotating celestial spheres within which they were embedded, Kepler posited the planets were pushed around by the sunspecks of the rotating Sun, and Descartes that they were swept around by vortices, and heliocentrism was accepted long before the Thomist-Keplerian doctrine of inertia that bodies inherently resist ALL motion was rejected in favour of Newton's minor revision of it that they resist all motion EXCEPT uniform straight motion. In particular Kepler adopted a Thomist 'inertial' variant of Aristotelian dynamics, according to which all bodies universally have a non-gravitational inherent resistance to motion proportional to their mass 'm', and whereby v α F/m. The radical historical importance of Kepler's 'inertial' astro-physics may be that it was the first astro-physics to theoretically anticipate novel facts before they were observed, for it successfully predicted the dramatic novel facts that the Sun and planets with satellites rotate, first confirmed by rotating sunspots in 1609(?) by the telescopic observations of Kepler's research assistant, John Fabricius. Because on Kepler's Aristotelian inertial dynamics orbiting satellites must be pushed around by something, he therefore posited the Sun and planets with orbiting moons such as Jupiter must all rotate in order to push their satellites around somehow. These were apparently the first successful theoretical novel predictions of heliocentric astro-physics, and on the Huyghens-Leibniz criterion that the greatest commendation of a hypothesis next to absolute proof is that it successfully predicts novel facts, they might explain the major conversion to heliocentrism soon thereafter. It is a major defect of the article that it entirely omits any mention of this historically highly important scientific development achieved by Kepler and contains no mention whatever of sunspots and of the dramatic theoretical significance of rotating sunspots. Arguably rotating sunspots provide the grail no historian of science has yet discovered, namely what makes the heliocentric revolution rational.

I shall leave you some time to revise the article yourself or else rebutt my criticism before I make any corrective deletions/revisions. But to make clear, you have my constructively critical support in making this a featured article. Whilst I cannot agree with Hegel and Popper that Kepler's scientific achievement was greater than that of Newton, I certainly agree they were far nearer the truth than the standard positivist account, if not for reasons they realised. For without Kepler's notion of 'inertia', rejected by Galileo but most keenly noted and critically revised by both Descartes and Newton, we would never have had Newton's historically crucial inertial dynamics. Season's Greetings. Logicus 20:40, 26 December 2006 (UTC)

Circular motion, etc.

Logicus has raised some interesting points; I've tried to address one of his comments that deals with circular motion by disentangling the concern of the natural philosophers with the causes of celestial motion from that of the mathematical astronomers' concern with geometrical models. Of course, these traditions interacted in complex ways, as many medieval astronomers also accepted the natural philosophers' teachings on the physical nature of the celestial spheres (remember Copernicus wrote De revolutionibus orbium celestium) and many medieval natural philosophers discussed the physical nature of the astronomers' epicycles and eccentrics. I hope my changes address some of his concerns about circular motions.

On a different point raised in the same paragraph, I'm not happy with Ragesoss's phrase "Further geometrical techniques were necessary to account for observed eccentricities:" The term "eccentricities" doesn't get at what the astronomers observed and what they were trying to account for using equants and the Tusi-couple. The principle astronomical phenomena at issue here included:

• The varying size of the retrograde arc in different portions of the zodiac.
• The varing intervals (either measured in space or in time) between successive synodic phenomena (i.e., first and last visibility, stationary points, and oppositions), which also varied as a function of the planets' position in the zodiac.

I'd like any suggestion for how to replace "observed eccentricities" with a compact phrase that encompasses what the astronomers were up to. "Observed zodiacal anomalies" would do it, but is too much heavy jargon for an encyclopedia article -- I never used it in an undergraduate lecture.

Happy Christmas to all SteveMcCluskey 15:14, 28 December 2006 (UTC)

Kepler did not discover non-circular planetary motion

Logicus comments: In 'Logicus Criticisms' above Logicus pointed out that the 'from circles to ellipses Kepler astronomical revolution' story is one of the sillier ahistorical aspects of the positivist Scientific Revolution fairy tale. But its arch-defender, Steve McCluskey, apparently wishes to preserve the myth of the alleged circularity of celestial motion of all pre-Keplerian celestial astronomy somehow. However, his 29/12/06 edit of the article's claim that

"Since antiquity, it was assumed a priori that the natural motion of the planets was circular..." to become

"Since antiquity, natural philosophers considered that the natural motion of celestial bodies was circular..."

to try and avoid Logicus's criticism completely fails for the most elementary logical reason. For of course the planets are themselves celestial bodies and indeed the only relevant ones for the modern reader who does not believe in or even know of 'the celestial spheres'. Yet their motion was thought to be non-circular ever since Apollonius's eccentric epicyclical astronomy in antiquity. And the planetary orbits were certainly not thought to be circular in the immediately preceding astronomical orthodoxy at the time of Kepler's Astronomia Nova, namely Tycho's Heraclidean geocentric astronomy in which planetary orbits were at least epitrochoidal around the Earth.

Thus the logic of scientific discovery and development is fundamentally misrepresented by such ahistorical positivist mythology, i.e. Kepler did not discover planetary orbits are non-circular. And McCluskey's 'natural philosophers versus astronomers' distinction is surely a red herring here, and anyway probably largely if not wholly a myth invented by positivist historians of science. Probably all or most astronomers since antiquity have been concerned with giving a physically realistic portrayal of the cosmos.

The whole 'Keplerian circular to elliptical planetary orbits revolution' claim is a historically untenable fundamentalist dogma of positivist revolutionist historiography, and must be totally rejected. For it does nothing but introduce obfuscatory and insoluble pseudo-problems without advancing our understanding of the logic of scientific discovery, which is the purpose of rational history of science. It is at best a misplaced kinematical misrepresentation of the really significant fundamental change in astro-physics, namely the dissolution of the solid celestial spheres and of the Plato-Aristotle heuristic programme of explaining planetary orbits by some mechanism of (nested and interconnected) uniformly rotating spheres. But as Kepler himself pointed out, this dissolution of the solid spheres was already accomplished in Tycho's prevailing geocentric cosmology. The latter implied solid spheres were impossible because of the intersecting orbits of Mars and the Earth. And their impossibility was further claimed to be supported by Tycho's independent evidence of the superlunary trans-spherical paths of comets that would have shattered any such solid spheres. So this fundamentally important change in astro-physical modelling is not attributable to the heliocentric revolution and moreover it preceded Kepler's Astronomia Nova. (Here I shall not enter into the ongoing fascinating debate over the possible novelty of the hypothesis of non-solid fluid celestial spheres in the 16th century and Kepler's (retro- ?) commitment to fluid orbital spheres that became Cartesian vortices.)

But not only is it false that planetary orbits were circular before Kepler, but the article's claim that in Astronomia Nova Kepler abandoned 'the Aristotelian principle of the primacy of uniform circular motion' is also apparently false. For according to Kepler's astronomy, the planets were primarily pushed in a circle around the Sun, but their essentially circular orbits were perturbed by alternating solar magnetic attractions and repulsions that produced non-circular elliptical orbits overall thereby. If so, from a logical point of view rather than abandoning the primacy of circular motion, surely Kepler's astro-dynamics retained it, as indeed did Galileo's. And Newton himself was not averse to charactersing the planetary orbits as essentially circular, such as in the Principia's final Scholium: "The six primary planets revolve about the sun in circles concentric with the sun, ..." (p940, Cohen & Whitman 1999 Principia)

In provisional conclusion, I propose the article's whole section from "Since antiquity..." to "...an ad hoc mathematical fix." in the Astronomia Nova subsection be deleted as logically and historically irrelevant, confused and highly misleading, and only raising problems it cannot resolve. (e.g. As philosophers of science know, ad hoc mathematical fixes are always logically possible, contrary to the article's claim that they were not.)

This proposal disposes of McCluskey's second point, but just to note that 'observed eccentricities' could be replaced by 'variations', then stating what these two variations are.

It would be helpful and timesaving if McCluskey could try to think through Logicus's criticisms and edits logically and desist in his swift knee-jerk usually logically mistaken responses, perhaps giving a day or so of serious coherent thought to the issue ? Logicus 18:55, 2 January 2007 (UTC)

Kepler's Laws and Newton

Logicus's discussion minimizing the relation between Kepler's laws and Newton's theory of gravitation raises a good point and then takes it too far. Admittedly Keplerian elliptical orbits only apply rigorously in a simple two-body problem, and Newton spent part of his Principia struggling to deal with motions involving three or more bodies. Furthermore, as Curtis Wilson long ago pointed out, Newton was concerned over the lack of precision of Kepler's laws ("Newton and Some Philosophers on Kepler's 'Laws'," Journal of the History of Ideas, 35 (1974): 231-258).

However, Newton deduced the inverse square law in the annus mirabilis of 1665 from considerations of the motion of the Moon and "from Kepler's rule of the periodical times of the Planets being in sesquialterate proportion of their distances from the center of their Orbs." (Westfall, Never at Rest, pp.143, 152). In 1684 Newton's manuscript De motu corporum in gyrum demonstrated all three of Kepler's laws from physical principles (Westfall, p. 404) Newton's Principia (1687) expands on those, including a demonstration that bodies moving under an inverse square force travel in paths described by conic sections, of which Kepler's elliptical orbits provide a special case(Principia, Book I,Sect. III, Prop. XI, Prob. VI; Prop. XII, Prob. VII; Prop. XIII, Prob. VIII; Prop. XVII, Prob. IX) a demonstration that bodies moving under a centrally directed force sweep out equal areas in equal times (Principia, Book I, Sect. II, Prop. I, Th. I; Prop. II, Th. II) and demonstrations that Kepler's 3/2 power law follows from inverse square gravitation (Principia Book I, Sect. III, Prop. XV, Theorem VII) and that Kepler's 3/2 power law is inconsistent with Cartesian vortices (Principia, Book II, Prop. LII, Theorem XL, Scholium). Addressing the more complex case of many bodies, Newton found that these bodies "may move among themselves in elipses; and that the radii drawn to the foci describe areas very nearly proportional to the times" (Principia, Book I, Proposition LXV, Theorem XXV). To speak of perturbed elliptical orbits does not sound at all like a falsification of Kepler's theory.

The influence of Kepler on Newton is complex and should not be oversimplified, but it cannot be ignored, to say nothing of being turned into opposition. --SteveMcCluskey 01:57, 29 December 2006 (UTC)

Logicus comments: Thanks for all this, and will respond as most appropriate. But since at least you do not disgree that Kepler's laws were not the foundation of Newton's gravity theory, I shall delete the logically mistaken claim that they were. Logicus 17:04, 29 December 2006 (UTC)

Sed contra. I thought I made it clear that one of Newton's two original derivations of his law of gravity was based on Kepler's third law and that the third law (as well as the other two) continued to play an important role in Newton's Principia. That's pretty clear evidence that Kepler's laws were one of the foundations of Newton's gravity theory. I don't want to get into a revert war, but Kepler's influence on Newton is an important element of Kepler's significance and should remain in the article. --SteveMcCluskey 17:43, 29 December 2006 (UTC)

Logicus Delete re Orbits

"The very idea of an orbit, a trajectory through space, may have been the most revolutionary aspect of the New Astronomy. All earlier astronomers, including Copernicus, conceived of the planets as dense spots within a system of orbs, spherical shells that rotated to produced the observed motion of planets; a planet's distance from its center of rotation based on many points was assumed constant. [17]"

This paragraph must be deleted. Contrary to its first sentence, Field 1988 [See Further References] tells us Kepler "does not use the word orbis in a way which would allow us to translate it as 'orbit' i.e. the planet's actual path in space." [p86, Field 1988] And contrary to the second sentence, (i) Tycho's geocentric astronomy did not 'conceive of the planets as dense spots within a system of orbs' since it abolished the solid orbs, and (ii) a planet's distance from its center of rotation based on many points was not assumed constant at least since epicyclic astronomy.Logicus 19:13, 2 January 2007 (UTC)

Kepler never abandoned his Mysterium Cosmographicum's polyhedral-spherist astronomy

The article currently claims "[In his 'Astronomia nova'] Kepler set about creating - literally - a new astronomy. Though it meant abandoning his system from Mysterium Cosmographicum,...."

But Astronomia Nova was not the abandonment of the 1596 Platonist polyhedral-spherist cosmology of Mysterium Cosmographicum, but rather an integral part of its further development concerned with determining more accurate dimensions of the planetary orbs/spheres. This claim that Kepler abandoned the Platonist astronomical cosmology of Mysterium Cosmographicum in his Astronomia Nova and thereafter is just yet another apocryphal part of the positivist fairy tale of a Scientific Revolution that typically air-brushes out the fact that Kepler republished a much expanded version of the former in 1621. This article's current list of 'Writings by Kepler' very notably omits it, apparently in line with positivist air-brushing. In fact Kepler's 1619 Harmonices Mundi and his 1621 Mysterium Cosmographicum Ed2 were both further developments of his 1596 polyhedral-spherist astronomy. As Field, the English historian of science and student of Rupert Hall, wrote in his 1988 'Kepler's Geometrical Cosmology' (his PhD thesis supervised by Hall) cited in the article's Bibliography: "The fact that Kepler allowed a second edition of the Mysterium Cosmographicum to be printed in 1621, in itself suggests that the amount of astronomical work which he had done in the meantime had not led him to reject the theory put forward in this early publication." [p72 Field 1988]

The anti-positivist analyses of Kepler's astro-physics in the works of both Field and Stephenson cited in the Bibliography provide a valuable antidote to the historically mistaken positivist analysis of it favoured by Ragesoss and McCluskey. Logicus 18:54, 3 January 2007 (UTC)

Logicus Deletes

(i) The introductory Carl Sagan quote "Nevertheless he was, in the words of Carl Sagan, "the first astrophysicist and the last scientific astrologer" must be deleted as patent historical nonsense given there were scores of ancient Greek astrophysicists and no doubt preceding ancient Egyptian and many others. And Kepler himself was essentially a developer of Plato's Timaeus astro-physics.

(ii) p4 "Though the essay did not earn him a place in Ferdinand's court, its proto-gravitational theory became the basis for his later work on planetary motion." Kepler's gravitation theory was not the basis of his later work on planetary motion. Kepler held and developed a Platonic cognate mutual attraction theory of gravity such as adopted in 14th century Parisian physics and also held by Galileo, a theory analogous to Plato's theory of mutual human attraction in which like bodies (cognates) attract each other. And according to Kepler's version of it, the Earth and Moon are cognates and thus mutually attract each other, but the planets are not cognates of each other nor of the Sun, whereby there are no gravitational attractions between these latter bodies. (In Galileo's universal gravitation theory, at least in his celestial cosmogony, the planets are cognates of the Sun and thus fall towards it according to Galileo's radically mistaken universal law of gravitational fall, s α tt/2.) Hence Kepler's gravitation theory was not the basis of his later theory of the causes of planetary motion. To what extent it may have played a role in his theories of the motions of planetary satellites such as the moons of the Earth and of Jupiter is another matter.

(iii) p6 "Having given up on circular orbits,..." is nonsense since he had never proposed circular orbits in the first place.

(iv) The Caspar quotation "Epitome ranks next to Ptolemy's Almagest and Copernicus' Revolutiones as the first systematic [complete] presentation of astronomy to introduce the idea of modern celestial mechanics founded by Kepler." is confused gobbledegook and must be deleted. What on earth does it mean? What kind of ranking is being claimed here, rank 2 or 3 in respect of what ? For neither Ptolemy's Almagest nor Copernicus's work were introductions to Kepler's celestial mechanics and thus unrankable in that league. And nor did Kepler found modern celestial mechanics, but rather Newton did, unless the reference is to Kepler's Thomist inertial-dynamics further refined by Newton. And surely it was the 1609 Astronomia Nova, not the 1618 Epitome, that founded Kepler's celestial mechanics of the Sun pushing the planets around in circles perturbed into ellipses by secondary magnetic forces. Logicus 19:09, 4 January 2007 (UTC)

Instead of deleting these things, which are cited and attributed to the people who made the claims, you should add balancing information from contradictory sources. I've restored these three deletions; it's not our place to argue against sources, but rather to show the different interpretations that have been published.--ragesoss 16:40, 6 January 2007 (UTC)

I'm grateful for all the attention you're giving this, as I would like to keep this article as neutral as possible and I realize that the sources I've used are not the final word (and in many cases, probably not the best). But it seems like the traditional interpretation (a la Caspar) is the most widely known, so alternate interpretations should be in addition to that.--ragesoss 16:45, 6 January 2007 (UTC)

Was Kepler's first law a rash conclusion ?

The article claims "Finding that an elliptical orbit fit[ted] the Mars data perfectly, [Kepler] immediately concluded that all planets move in ellipses, with the sun at one focus - the first law of planetary motion."

This claim seems to be asserting that Kepler irrationally concluded all planets move in ellipses with the sun at one focus from just one example, namely Mars, before first checking whether it was also true of the data of any of the other 5 planets' orbits, hence practicing a remarkably non-empirical and 'unscientific' method. But was this so ? This is notably the traditional illogical farce of the positivist inductivist fairy tale told by such as Caspar and Koestler of Kepler's supposedly revolutionary scrupulous commitment to the 'empirical' precision of his hypotheses in conforming to the data on the one hand. But on the other hand, in this tale, after intensely indulging this worthy empirical commitment for the case of Mars, Kepler then suddenly leaps to the conclusion that his elliptical hypothesis must be true for every planet without any mention of him ever checking it against the data for any other planet, and thus checking such as whether their orbits were ovoid or elliptical, for example.

Are the claims made true ? Did the ellipse hypothesis really curve-fit the Mars data PERFECTLY ? Did Kepler really not check his first law against the data for any other planet first before publishing it ? Did Tycho's data for Saturn confirm the ellipse law ? What are the literary references for discussion of these centrally important issues with respect to the logic of scientific discovery ? The article should surely discuss such issues. Meanwhile I propose this sentence be deleted unless or until its two claims are reliably referenced.

One of the key elements of Kepler's historical significance is his supposed steplifting the criterion of observational accuracy in theoretical astronomy and his innovation of the notion of 'experimental error'. This reputation needs serious qualification if he did not test his orbital hypotheses for every planet. Logicus 19:09, 4 January 2007 (UTC)

Logicus explores this issue further: It seems likely Kepler did publish his law of elliptical planetary orbits in Astronomia Nova before testing it for any planets other than Mars. In his book The Astronomical Revolution Koyre published a letter of March 1607 from Kepler to his patron Emperor Rudolph II for more money to extend his Astronomia Nova analysis and its successful 'war against Mars' to all the other planets. But none was forthcoming. [See Part 2 Kepler and the New Astronomy, Ch IX Astronomy with the Ellipse, p277-8 of 1973 Hermann Paris edition of The Astronomical Revolution]

And according to Pannekoek in his A History of Astronomy, it was not until his 1618 Epitome that Kepler first gave the orbits of Mercury and Venus with their eccentricities and aphelions as completely regular ellipses. But Pannekoek comments:

"How Kepler derived them from the observations is nowhere explained [in the Epitome]. In a letter of May 5 1616 to his former teacher Maestlin he merely says "In the summer of 1614 the theory of Venus followed, in the winter of 1615 that of Mercury: they are in no way peculiar as compared with Saturn, Jupiter and Mars;... " " [p242 A History of Astronomy]

This raises at least two questions. First, did Kepler claim the orbits of Saturn and Jupiter were also elliptical and provide their parameters, and secondly, where if anywhere between 1607 and 1616(?) did he get the observational data to confirm the orbits of all the other five planets were regular ellipses, if indeed he did ? Or did he simply blag it ? Does anybody know ?

This information also provides an interesting light on Ragesoss’s misquotation of Caspar as claiming Epitome was "the first systematic [complete] presentation of astronomy to introduce the idea of modern celestial mechanics founded by Kepler." that omitted the word 'complete'. For it may be that Caspar was implicitly acknowledging that Astronomia Nova was radically incomplete in respect of not establishing its planetary theory empirically for any other planet but Mars. Logicus 15:31, 6 January 2007 (UTC)