Talk:Johannes Kepler

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Featured on Template:March 8 selected anniversaries (may be in HTML comment) 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.

• (1) 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.

• (2) 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.

• (3) 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)

Testing the Rudolphine Tables: Re point (1) above, it seems that on the one hand the 1639 transit of Venus, specifically observed by the English astronomer Jeremiah Horrocks for that critical purpose, was regarded as a falsification of the Rudolphine Tables because they did not predict Venus would appear in the sun’s disc, and on the other hand a confirmation of Lansberg’s competing astronomical tables based on epicyclical astronomy which did predict it. [See Dreyer.] Logicus 15:44, 7 January 2007 (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)

I'll have to re-check out the book I had cited for that, and compare some other sources. I know that Andersen, Barker and Chen, among others put a lot of emphasis on Kepler's orbits being revolutionary, but re-reading what I wrote it seems a bit off (especially with respect to the Tychonic system, as you point out). Something should definitely be said about the emergence of the orbit concept, balancing the different interpretations.--ragesoss 17:18, 6 January 2007 (UTC)

Logicus to Ragesoss: In general re your ideological interest here in finding something revolutionary in the astronomy of Kepler's Astronomia Nova, the only significantly historically novel aspect of it I am aware of is that it was the first development of the Aristotelian inertial dynamics developed by Averroes and Aquinas for a heliocentric model. But it was not thereby revolutionary nor in any other respect I am aware of. But of course in the advertising industry and revolutionist historiography of science everything is 'a revolutionary new product', and so possibly Kepler's orbits are for such as revolutionists Andersen, Barker & Chen. But obviously such claims without serious proof are not to be taken seriously. For clearly the concept of a planet having a non-circular re-entrant closed curve trajectory was not original to Kepler; see for example the ovoid orbit for Mercury depicted in the 1558 Rheinhold edition of Peuerbach's astronomy on p341 of Gingerich's 1993 book The Eye of Heaven cited in the Bibliography. And since the notion of a planet performing a trajectory in space without being embedded in an orb is obviously also pre-Kepler and indeed ancient, why bother with such an abstruse issue in an article on Kepler ? Inasmuch as the purpose of history of science is to help determine the logic of scientific discovery and development, identifying exactly what was specifically historically novel in Kepler's work and its problem-solving rationale by means of critical logical thinking is surely more important than repeating the unreliable illogical nonsense spouted by historians of science about what was. Logicus 19:06, 9 January 2007 (UTC)

First of all, I deny any ideological interest in finding something revolutionary in Astronomia Nova; I simply wrote this article based on the sources I was most familiar with, on the assumption that others could help balance the article in areas of historical dispute. Granting that the source I had used might not be significant enough to warrant inclusion, the idea of Astronomia Nova being revolutionary is a strong and recurring idea in the historiography; mistaken or not, it's an issue that needs to be in the article (along with contrary views attributed to other historians). It is beyond the proper domain of a Wikipedia article to make the kind of decisions about which experts are right and which are wrong that you seem to be asking for. It's not our place to investigate the logic of scientific discovery, but simply to provide a biography of Kepler, based on existing literature by experts.--ragesoss 19:20, 9 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.) 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)

Logicus justifies his deletes contra Ragesoss reverts

- Delete (ii): But contrary to what Ragesoss claims at 16:40 6 Jan, no source is given for the blatantly false claim that "...its proto-gravitational theory became the basis for his later work on planetary motion." And re the proximately surrounding footnote references 9 & 10, certainly Caspar makes no such claim on his pages 108-111. But as Dreyer correctly wrote "gravity had no place in Kepler's theory of celestial mechanics." [p398, Dreyer], meaning it played no role whatever in explaining planetary orbital trajectories dynamically. I therefore propose deletion at least until Ragesoss can find a source that makes this apparently ludicrously mistaken claim.

- Delete (iii): Thanks at least for accepting this deletion. My critical comment was of course intended to refer to 'concentric' circular orbits, since of course Kepler attempted an eccentric circular solar orbit for Mars, whereas the logical contrast of varying distance you make supposes concentricity.

- Delete (i): I disagree with Ragesoss's advice here to add balancing information rather than simply delete the claim made by Wikipedia that Kepler was the first astrophysicist. Historians of science make all sorts of claims, including very many very silly ones, so why repeat them all and set many mad hares running, rather than judiciously ignore those that are blatantly false ? Arguing against sources is also avoided by not quoting them in the first place. Contra Sagan and some others, very obviously Kepler was not historically the first astro-physicist, but was simply restoring causal astro-physics against Tycho's immediately preceding abandonment of it. The polemical 'New' of 'The New Astronomy' was only directed against the prevailing Tychonic astronomy, not the whole history of astronomy. Thus Gingerich gets it right that Kepler's astronomy was only a RESTORATION of celestial physics, contra Tychonic purely kinematical astronomy, rather than its wholly novel historical innovation, when he says:

"[Tycho Brahe] had considerable difficulty in accepting [Copernican astronomy] as a physically real system because it contradicted the accepted Aristotelian physics and apparently also the Bible. Unwilling and unable to forge a new physics, he chose instead to modify the cosmology to the geo-heliocentric form. Of course, this shattered the crystalline spheres, a radical step he eventually espoused. That left the heavens with no obvious means of generating their motions, something previously supposed to have been supplied by God at the outside edge of the nested spheres and transmitted inward through the crystal machinery. It is at this point in the story that the young German astronomer Johannes Kepler arrived on the scene, eager to RESTORE some kind of celestial physics." [p36, Gingerich 1993]

So I propose deletion rather than repeating patently silly opinions that then require correcting sources. Or do you want to add something like '...however Gingerich has pointed out Kepler's was only restoring astro-physics after its recent abandonment by the prevailing Tychonic astronomy.' But why get into such a silly issue in the first place ?

Whether Kepler was or was not the first astrophysicist (an arbitrary designation in any case) is beside the point of quote, in my view. I agree with you that Sagan's quote is, historically speaking, indefensible. But it emphasizes the way Kepler is seen as a central figure in the foundation of modern science; Sagan is was not a historian but (in this context) a science popularizer, and it is that capacity that the quote is most significant. By "astrophysicist", Sagan implied "modern astrophysicist" and thus implied that modern physics (in the traditional Sci Rev sense) began with Kepler; this is a lot of philosophical baggage in the quote, but it's pithy. Fortunately, by using Sagan's word's, the article does not commit itself to any of that philosophical baggage. I think a good solution to your objection would be to expand the footnote for that quote to include something along the lines of your summary of Gingerich here. Of course, Gingerich largely endorses the standard idea of the Scientific Revolution; by "some kind of celestial physics", I think Gingerich means to emphasize that the physics that developed following Kepler was a different kind of physics.--ragesoss 19:06, 10 January 2007 (UTC)

-Delete (iv): Ragesoss seems to completely miss the illiteracy point here, which is that with or without the missing word 'complete', Caspar's quotation simply does not make any plain English sense. Even if Epitome was the first complete systematic presentation of Kepler's celestial mechanics for all the planets, nevertheless how on earth can it be compared with Almagest and De Revolutionibus in that respect ? The claim is incoherent gobbledegook, unlike for instance Dreyer's intelligible equal ranking claim about Astronomia Nova, also quoted by Gingerich, "In the history of astronomy there are only two other works of equal importance, the book De revolutionibus of Copernicus and the Principia of Newton." [p410] The Caspar quotation must be deleted simply on the grounds of its unintelligibilty, and if required, replaced by some intelligible claim.

Logicus will respond more fully to the issues raised in 16:45 6 Jan later. But Caspar's interpretation is surely not the traditional nor most widely known interpretation of Kepler, who in school physics is misrepresented as a positivist scientist who just discovered some kinematical laws of astronomy by deducing them from data. As I recall Caspar's book was much concerned with challenging this Gradgrind positivist conception of Kepler's theorising. Logicus 18:39, 10 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)

Thanks for catching that missing word. I think that's right that Caspar was acknowledging that Astronomia Nova was incomplete.--ragesoss 17:11, 6 January 2007 (UTC)

GA nomination

Well, I read this article and found it to be exemplary, but let's go through the motions anyway

1. Well written -pass
2. factually accurate and verifiable - pass
3. broad in coverage - pass
4. neutral - pass
5. stable - pass
6. images - pass

Overall, I'm very happy to make this a Good Article. Deyyaz ^{[ Talk | Contribs ]} 18:31, 6 January 2007 (UTC)

I wouldn't be so sure about the stable part, as it just went through a complete re-write and there are there are lots of bugs to work out, but thanks.--ragesoss 18:40, 6 January 2007 (UTC)

As yet Logicus cannot give passes at least for 2, 3 and 4, but works towards improvements to that end. Logicus 19:08, 10 January 2007 (UTC)

Kepler's laws falsified by transits of Mercury and Venus

NB This discussion continues the above discussion "Was Kepler's first law a rash conclusion ?". Check it out first as an orientating introduction.

From the above discussion it seemed from Pannekoek's critical comments that suggest Kepler never provided any evidential proof that his first two laws of planetary motion proclaimed in his 1609 AN squared with the observational data for any planet other than Mars, if indeed he even did that. But at least in a letter to Maestlin in 1616 Kepler seemed to claim he had established this at least for Venus and Mercury in 1614 and 1615 respectively, that is at least 5 years after he had published Astronomia Nova. However, other commentaries from historians of science suggests the 1631 and 1638 transits of Mercury and Venus respectively falsified Kepler's laws and his 1627 Rudolphine Tables on Kepler's own criterion of falsifying discrepancies between theoretical prediction and observation, as follows:

- The 1631 transit of Mercury

According to Owen Gingerich's account of the episode [in his book The Eye of Heaven published by The American Institute of Physics in 1993], it seems that the 1631 transit of Mercury falsified Kepler's elliptical laws and Rudolphine Tables on Kepler's own criterion of a sufficient degree of observational error to falsify Ptolemaic astronomy and a circular or ovoid orbit for Mars. For by the same token that Kepler regarded a divergence between theoretical prediction and data of as little as 8' of arc as having falsified a circular orbit for Mars (and also an ovoid orbit), eventually in favour of an elliptical orbit, on just as strict a Keplerian criterion of an unacceptable degree of observational error it seems the transit of Mercury falsified an elliptical orbit or the second law, since it diverged from the Rudolphine Tables by even more than 8', namely by 10' of arc according to Gingerich. [See p342, Gingerich 1993.]

Thus from a logical point of view as opposed that of historians of science, Gingerich's conclusion that "Kepler did not live to see his prediction fulfilled" should rather have been "Kepler did not live to see his prediction refuted on his own criterion of a falsifying degree of observational error."

And his conclusion that "the evidence for the new system was overwhelming" overlooks the glaring question of why a discrepancy of 8' of arc refuted circular and ovoid orbits for Mars, but an even greater discrepancy of 10' of arc was overwhelming evidence that Mercury's orbit was elliptical or obeyed Kepler's laws, rather than evidence that however good, they were also false. Some astronomers might well have been underwhelmed.

Kepler himself had written on the 8' Martian discrepancy's falsification of Ptolemaic astronomy as follows: "God's goodness has granted us such a diligent observer in Tycho Brahe that his observations convicted the Ptolemaic calculation of an error of 8' of arc. It is therefore right that we should with a grateful mind make use of this gift to find the true celestial motions." [p178, Kepler's 1609 AN, quoted by Gingerich on p312]

The logically analogous Keplerian conclusion from the 10' discrepancy in Mercury's 1631 transit would have been:

'God's goodness has granted us such a diligent observer in Gassendi that his 7 November 1631 observations in Paris of the transit of Mercury have convicted Kepler's planetary laws of an error of 10' of arc. It is therefore right that we should with a grateful mind make use of this gift to find the true celestial motions.'

Whether this is yet another example of the inability of historians of science to achieve logically joined up thinking and proof-read their works for logical consistency, or there is some absolving but unstated technical explanation, is at least a question that should be posed here. Whilst the fact reported by Gingerich that other Ptolemaic and Copernican tables were 5 degrees out on this transit and thus worse than the Rudolphine Tables in this prediction does not absolve the latter from falsification by 10' of arc on Kepler's own criterion. Moreover, any mention of the maximum discrepancy between Kepler's elliptical Martian orbit and Tycho's data is hardly readily forthcoming in the literature. Did Kepler's elliptical Martian orbit improve on the maximum 8' of arc discrepancy for circular and ovoid Martian orbits ? Gingerich's computer analysis reported in his 1971 essay 'The Computer versus Kepler Revisited' revealed "The best possible solution with this type of model, as stated previously, leaves errors up to 8' of arc." We are not told what maximum discrepancy Kepler himself identified or reported, if any, for his proposed elliptical orbit, and thus what amount of discrepancy less than 8' he regarded as acceptable.

- The 1639 transit of Venus

In discussing the reception of Kepler's planetary laws and his Rudolphine Tables based on them, Dreyer reports that the Copernican astronomer Philip Lansberg (1561-1632), who rejected Kepler's planetary theories. published planetary tables in 1632 founded on an epicyclical theory that were used by many astronomers. And Dreyer says of them "They probably owed a great deal of the good repute they enjoyed for some time to the circumstance that they by a fluke represented the transit of Venus in 1639 fairly well, while the Rudolphine Tables threw Venus quite off the Sun's disc." [p420, Dreyer.] But Dreyer does not explain why this comparative success for Lansberg's tables was no more than a fluke. So it seems the 1639 transit of Venus was regarded as refuting the Rudolphine Tables' prediction, but corroborated Lansberg's tables in something of a crucial experiment against Kepler that made Lansberg's epicyclical heliocentric tables more popular than elliptical heliocentric the Rudolphine Tables with scientists who valued greater observational accuracy.

Did Kepler fit elliptical orbits for every planet to within less than 8' of arc observational error for Tycho's data ?

There is much mindless and glaringly illogical celebratory hagiography on Kepler in the positivist religious literature, but little critical scientific analysis of the most elementary questions such as this that the reader of an Encyclopedia might wish to know. Even the proclaimed 'great American detective' of the history of astronomy, the Harvard academic Gingerich, much concerned with proclaiming Kepler's alleged improvement of astronomical accuracy, never claims improvements over rivals for any planet other than Mercury in his cited 1993. In fact Gingerich's silence tends to confirm Pannekoek's analysis that nowhere did Kepler ever demonstrate how his laws squared with the data or not. And he at least reveals the elliptical orbit for Mars was no better than its circular and ovoid rivals with respect to maximum discrepancies with Tycho's data. But if the answer to our question is that Kepler did not even fit an elliptical orbits for Mars to less than 8' error, what horrors might be revealed by his curve-fitting ventures for other planets. The 10' error for the Mercury transit may only be the thin end of the wedge. Logicus 19:12, 10 January 2007 (UTC)