Talk:Copernican heliocentrism

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Accuracy of the Copernican System[edit]

The article currently says "Copernicus' system was not experimentally better than Ptolemy's model". For any one planet, a geocentric system with one circular epicycle is exactly equivalent to a heliocentric system with circular orbits. However such a geocentric system allows two parameters for each orbit (the radius of the deferent and the radius of the epicycle) wheras the equivalent heliocentric system has only one parameter per orbit plus one for the system as a whole. On the face of it, under these circumstances, the geocentric system should produce more accurate predictions.

Actualy, both the geocentric and heliocentric systems were more complicated than this. Copernicus allowed more epicycles and Ptolomy allowed non-uniform motion (according to Gingerich). It seems likely to me that the non-uniform motion would still produce more accurate results. Anyone know whether this is true? Rjm at sleepers 07:59, 27 March 2007 (UTC)

Phases of Venus[edit]

This article and Gingerich both assert that observation of the phases of Venus provided a proof of heliocentrism. It seems to me that there would be phases of Venus on a geocentric system as well. Can anyone offer an explanation? Rjm at sleepers 10:17, 27 March 2007 (UTC)

Check out Kuhn's description and figures in The Copernican Revolution. Venus would have phases in a geocentric model, but the pattern would be different (for example, never close to a fully illuminated disk for Venus, if the Sun's orbit around the Earth is placed outside of that of Venus, the convention at the time). Galileo observed the pattern of phases at different angular distances from the Sun that matched the heliocentric model. Xanthoptica (talk) 04:12, 14 October 2009 (UTC)

Uniform circular motion[edit]

The most recent revision, which does a good job of tidying the text, has also removed the comment that Copernican heliocentrism reinstated uniform circular motion. I'm not sure why this was removed. Gingerich makes the point that this was why astronomers pursued it prior to Kepler. Pending discussion, I've added a brief comment. Rjm at sleepers 05:31, 21 April 2007 (UTC)


Pleroma has introduced the idea that Galileo's discovery of sunspots with telescope was a factor in the acceptance of heliocentrism. But, I understood that sunspots had been observed long before the discovery of the telescope and in anycase, they don't contradict geocentrism. Sunspots do strike a blow at the idea that the heavens are unchanging, but so do comets and supernova. Rjm at sleepers 05:44, 21 April 2007 (UTC)

Link to analysis of De revolutionibus[edit]

May I suggest the following (which I wrote): . De revolutionibus is a bastard of the book to read and there is very little anaylsis on wikipedia of its contents (beyond a list of books) or the arguments that Copernicus uses to make his points. The suggested article is a reasonably detailled explanation of what Copernicus was doing and howe he got his message across. I think it helps explain the reception of his work. James Hannam 08:44, 17 August 2007 (UTC)

The article is clearly relevant and of high quality, so I've added a link to it under "Further reading" here and at De revolutionibus orbium coelestium. Thanks for noting it. EALacey 09:26, 17 August 2007 (UTC)

Apparent confirmation[edit]

Apparent confirmation of Copernican heliocentrism was also provided by Bradley's abberation of 1725, 1727, 1728 and 1729 and by Foucault's pendulum experiment of 1851. Obviously, one was before Bessel's work and one after. —Preceding unsigned comment added by (talk) 10:21, 5 March 2009 (UTC) Henderson and Struve were working at about the same time as Bessel. —Preceding unsigned comment added by (talk) 10:34, 5 March 2009 (UTC)

Is this a useful page?[edit]

This page doesn't seem to add much to the Heliocentrism page - there's more detail there, and Copernicus is put into a broader context. It seems that either we should pull the Copernicus-specific stuff into this page (which is a lot of the latter part of the Heliocentrism page) or get rid of this page with a redirect to Heliocentrism. Xanthoptica (talk) 06:09, 14 October 2009 (UTC)

Retrograde motion[edit]

I have removed the following: "Another attraction was the explanation of retrograde motion of the planets as an apparent motion, produced by observing the planets from an Earth that revolved around the Sun." I am not aware of a source for this and in anycase, the Copernican model retained epicycles and real retrograde motion. Rjm at sleepers (talk) 08:23, 17 October 2009 (UTC)

It is fairly easy to find good sources for that observation—which, from a modern point of view, is really the only advantage Copernicus's theory had over the Ptolemaic. I'm not sure what you mean by saying that the Copernican model retained "real retrograde motion". It's certainly not true that any of the planets themselves underwent real retrograde motion. Their actual motions were all prograde with roughly the correct angular velocities about the sun. It's true that Copernicus still used lots of epicycles, but none of them had a large enough effect to produce anything near a real retrograde motion in any of the planets. Their effects were limited to producing relatively small variations in characteristics of the planets' orbits (such as their eccentricities, distances from the Sun, directions of their lines of apses, planets' speed etc.). I'll add a couple of good references and reintroduce a revised version of the sentence which more closely reflects what those sources say.
David Wilson (talk · cont) 12:02, 18 October 2009 (UTC)

Precession of the equinoxes[edit]

The current text asserts that Copernicus "explained the precession of the equinoxes correctly by a slow change in the position of the Earth's rotational axis." AFAIK, he explained the precession of the equinoxes by the addition of a further rotating sphere (Koestler, pp. 579 & 580 in my edition). I have removed this, so revert me if I am wrong. Rjm at sleepers (talk) 08:26, 19 October 2009 (UTC)

Biblical reference[edit]

Bibletruthistruth added "Actually, this is an incorrect quote. According to Joshua 6:12 "And Joshua rose early in the morning, and the priests took up the ark of the LORD." KJV. No where in the bible is planet orbits around the sun mentioned.)" I have changed the chapter and verse to what I believe to be the correct one. My understanding of the argument used against heliocentrism is that Joshua commanded the sun to stop, not the earth. Therefore it was the sun not the earth that was moving. I don't think anyone ever suggested the bible described planetary orbits. Rjm at sleepers (talk) 06:38, 7 January 2010 (UTC)

Stellar parallax[edit]

if anyone is competent to expand on this, I'd like to read in this article about how the prediction of stellar parallax influenced adoption of copernican heliocentrism. I don't understand why it wasn't seen as a fatal flaw of the theory before it was detected in early 18th century, particularly when tychonic system didn't suffer of such flaw (did it have other flaws - or was just less elegant?)

This passage, apparently referencing Khun, seems strange in this light "Tycho Brahe went so far as to construct a cosmology precisely equivalent to that of Copernicus, but with the Earth held fixed in the center of the celestial sphere instead of the Sun" - Does the source actually say 'went so far'? and 'precisely equivalent'? Even if this is the case, the claim should be moderated by another source - for instance the article on parallax says "it was one of Tycho's principal objections to Copernican heliocentrism that in order for it to be compatible with the lack of observable stellar parallax, there would have to be an enormous and unlikely void between the orbit of Saturn and the eighth sphere (the fixed stars)" and gives a reference (See p.51 in The reception of Copernicus' heliocentric theory: proceedings... ISBN 9027703116, ISBN 9789027703118).

Article on tychonic system has a more precise claim on the equivalence: "It can be shown through a geometric argument that the motions of the planets and the Sun relative to the Earth in the Tychonic system are equivalent to the motions in the Copernican system." - so the motions of planets and Sun, but they do have distinct predictions of the motions of stars. On casual examination, it looks like tychonic model was a better fit with then known facts than copernican model. Aryah (talk) 07:19, 3 June 2010 (UTC)

Removed sentence that suggests Galileo predates Copernicus[edit]

I have pulled out this sentence from the article for two reasons: 1) It gives the impression that Galileo predated Copernicus, and 2) it doesn't contain enough detail about this motion to be clear, in contrast to the the lengthy discussion of uniform circular motion vs. uniform angular motion in the sections above. Perhaps someone more knowledgeable than I would like to expand on and clarify this aspect of the Copernican model in the article?

He added another motion to the Earth, by which the axis is kept pointed throughout the year at the same place in the heavens; since Galileo Galilei, it has been recognized that for the Earth not to point to the same place would have been a motion.

Jrauser (talk) 16:14, 31 July 2010 (UTC)

Earth at the center[edit]

I am wondering why it is more correct to say that Ptolemy put Earth "at the center" rather than "near the center". Ptolemy used eccentrics, which literally meant that the Earth was not at the center of the orbs. Furthermore, I am not sure it even makes sense to talk about the "center of the universe" with Ptolemy. I don't think that his deferents were concentric (ie, they did not have a common center), so the center of the universe is not something that he even defined. So it seems to me that the Earth was near the centers of the deferents, but that is about all that you can say with Ptolemy. Roger (talk) 15:31, 15 March 2011 (UTC)

" ... the center of the universe is not something that he [Ptolemy] even defined."
Nonsense. In Ptolemy's cosmography the outermost surface of the Universe is defined by the sphere of fixed stars. In chapter 2 of book I of the Almagest he contends that the Earth "lies right in the middle" of it, "like a geometrical centre", and in chapter 5 he gives detailed arguments to support that contention. In his mathematical model, the whole kit and caboodle rotates once per sidereal day about an axis directly through that centre, and the Earth is taken to be located precisely at it.
David Wilson (talk · cont) 13:26, 16 March 2011 (UTC)
Okay, so Ptolemy said that the Earth is at the center of the fixed stars. And of the daily rotation. But it is not at the center of the Mars deferent, and not at the center of any of the other orbs. Saying that the Earth is the center of the universe implies that the Earth is the center of everything, and that goes beyond what Ptolemy actually said. Roger (talk) 14:53, 16 March 2011 (UTC)
I flatly disagree with your assertion that saying the Earth is the center of the Universe must be interpreted as implying that the Earth is the "center of everything". More to the point, however, is that scholars of the history of astronomy don't seem to agree with you either. On page 64 of From Eudoxus to Einstein, for example, Christopher Linton writes: "Ptolemy did use physical arguments to justify his choice of a fixed Earth at the centre of the Universe" (emphasis mine).
David Wilson (talk · cont) 17:12, 16 March 2011 (UTC)

Arab influences[edit]

The article's current list of Arab influences is:

Several Muslim astronomers also had discussions on the possibility of heliocentrism, such as
  • Ibn al-Haytham, The 'first true scientist' (al-Hassan Ibn al-Haytham - this guy seems to be pivotal)
  • Abu-Rayhan Biruni,
  • Abu Said Sinjari,
  • Najm al-Dīn al-Qazwīnī al-Kātibī, and
  • Qutb al-Din al-Shirazi.

The list seems to be grabbed from air, it should instead be SeP: Copernicus:

  • Nasir al-Din Tusi (1201-1274),
  • Muayyad al-Din al-Urdi (d. 1266),
  • Qutb al-Din al-Shirazi (1236-1311), and
  • Ibn al-Shatir (1304–1375),
  • Ali Qushji (1403–1474)

and it is a very speculative list. Is the current list maybe a little jagged? Rursus dixit. (mbork3!) 17:37, 9 August 2011 (UTC)

Sorry, ignore all of it! I didn't read correctly. Only consider the link! Rursus dixit. (mbork3!) 18:07, 9 August 2011 (UTC)

Alleged innovations[edit]

All or almost all of the innovations said to have been introduced by Copernicus were actually used by Aristarchus. — Preceding unsigned comment added by (talk) 16:24, 26 September 2011 (UTC)

Frames of reference[edit]

When mentioning Newton and general relativity as factors supporting the theory, it would also be nice to mention that with the idea of an inertial reference frame, the statements "the earth goes around the sun" and "the sun goes around the earth" finally became well-enough defined to be compared.

Similarly, the idea of a rotating reference frame finally allows discussion of whether "the sky rotates" or "the earth rotates". — Preceding unsigned comment added by (talk) 04:27, 30 September 2011 (UTC)

Requested Citations Provided[edit]

Requested citations about Muslim astronomers have been provided via BBC documentary. Videos on-location at the original sources and evidence are shown and assessed.

Prof. Jim Al-Khalili, University of Surrey, concludes his investigation into the relationship between science and Islam. He shows how the scientific revolution that took place in 16th and 17th century Europe had its roots in the world of medieval Islam. He travels across Iran, Syria and Egypt to discover the astronomical advances made by Islamic scholars through their obsession with accurate measurement. He then visits Italy to see how those ideas permeated into the West and helped shape the works of Copernicus.

Documentary: Science and Islam 3/3 BBC (talk) 16:53, 5 February 2013 (UTC)

I don't think you can use youtube as a source. Furthermore, the first part of your edit [1] but in reality, he owes almost nothing to ancient sources isn't supported by your paraphrase, above William M. Connolley (talk) 17:28, 5 February 2013 (UTC)
You see on-location live truthful evidence, so why can't we use Youtube as a source of transparency, integrity, and accountability. Your personal opinion about Youtube seems out-of-proportion without reasoning, and outweighed by the on-location live evidence.
I did not make any text changes, I only added the video source. It's about the Requested Citations only, this Youtube source complies with this request.
The Youtube video clearly shows Arabic text characters + alphabet related to data tables... Data tables are not inductive hypotheses, but moreover deductive hard raw data made from exact numeral measurements, so the wording about Muslim "theories" is incorrect. Prof. Al-Khalili also explains the motivation of Muslim astronomers to execute exact numeral measurements... proper timing of Muslim prayal, fives per day... and proper compass direction of prayal, namely towards Mecca (talk) 17:46, 5 February 2013 (UTC)
Stop your edit warring, Connolley. This place is for 2-way discussion and reasoning. Did you even watch the BBC documentary and Prof. Al-Khalilis' explanations with his finger touching the original source? (talk) 08:09, 7 February 2013 (UTC)
Errrr, in your last edit you cited an article, and it says: "There is no question but that Aristarchus had the priority of the heliocentric idea. Yet there is no evidence that Copernicus owed him anything. As far as we can tell both the idea and its justification were found independently by Copernicus."[2] --Enric Naval (talk) 10:40, 7 February 2013 (UTC)
Sorry, again, I made no text citations towards Aristarchus... check the sequence of logs. There is a mix-up between text pieces you are talking about, and the BBC documentary.
I only added the BBC documentary video as hard data evidence, in 2 sentences, and amended the 2nd sentence to correct the reference to Muslim theories (which is factually incorrect as you can see in the video and via Prof. Al-Khalilis's finger in the original source book from Copernicus). I'm sure I can find a BBC website about the documentary...
Here are a few "text websites" handling and summarizing the BBC documentary, so dont get hung up about "THE video"... we have valid 1st hand information on-location to cite on. Even Prof. Al-Kalilis wrote a blog article.
The Power of Doubt
BBC documentary on Science and Islam
Science and Islam: Part 3 - The Power of Doubt
The 'first true scientist' (al-Hassan Ibn al-Haytham - this guy seems to be pivotal) This is the smoking gun citation you requested.
Those other text pieces where added in-between from someone else... I'm not interested in talking about that... do what you want. Its only about the facts contained in the BBC documentary guided by Prof. Al-Khalilis. (talk) 14:14, 7 February 2013 (UTC)
I'm guessing that the first of those, from the Beeb, is typical of the rest. So, first and most obviously, this provides no support to your As a university-trained Catholic priest dedicated to astronomy, some attribute Copernicus' contributions to his alleged acquaintance with the Sun-centered cosmos of the ancient Greek Aristarchus, but in reality, he owes almost nothing to ancient sources. In fact it says the opposite. If you'd meant "ancient Greeks" by "ancient sources" you should have said so, and perhaps saved yourself some grief. But it still doesn't say that C wasn't influenced by the Greeks, no matter how you read it. Secondly, you still need a source for the Arabs doing heliocentrism William M. Connolley (talk) 16:05, 7 February 2013 (UTC)
Sorry, again for the 3rd time, I made no text citations... check the sequence of logs. There is a mix-up between text pieces you are talking about, and the BBC documentary. Those other text pieces where added in-between from someone else (maybe you to confuse this discussion)... I'm not interested in talking about that...
The reference to inductive Muslim "theories" is factually incorrect, as you can see in the video and via Prof. Al-Khalilis's finger in the original source book from Copernicus. Those Muslim sources are visibly and audibly deductive data tables painting heliocentrism. Copernicus operated with empirical hard raw data from accurate Muslim measurements and presented the Muslim data tables in his book.
Ibn_al-Haytham - Model of the Motions of Each of the Seven Planets > Wikipedia state-of-art with citations
Copernicus's book visibly includes Arabic text + characters, so your refusal to address the BBC documentary is not convincing. (talk) 17:45, 7 February 2013 (UTC)
The only reference to heliocentrism is in the next section: Ibn_al-Haytham#Other_astronomical_works. Someone claimed that he had written a book with the heliocentric system, but it can't be verified. --Enric Naval (talk) 22:52, 7 February 2013 (UTC)
In case IP 84.xx hasn't yet got one of his main points across, I will point out that the edits which William M Connolley reverted on February 5th, apparently under the impression that they were all the work of the same editor, actually comprised two sets. The first was performed from an IP address in ADSL pool of the Turkish firm Tellcom Kartal. The second was performed from an IP address in a broadband static pool of the German firm Deutsche Telekom AG. In view of this, I see no reason whatever to believe that these two sets of edits were made by the same editor. On the contrary, it seems to me fairly evident that they were made by different editors.
On the issue of the source which IP 84.xx wants to insert as a reference, I strongly agree that television documentaries, even by the BBC, are not reliable sources for historical facts of the kind it was being cited for. The section of the article where the insertion is being proposed is already very well sourced to the scholarly literature, and, with the possible exception of its final sentence, is an accurate and balanced account of what's in that literature. In any case, nothing in that section of the article, again with the minor exception of its final sentence, is contradicted by anything in the BBC documentary. Mr or Ms IP 84.xx has simply misunderstood it:
  • The book shown at 5:38 of the documentary, which "visibly includes Arabic text + characters", was not Copernicus's. It was a printed latin translation of al-Battani's astronomical works tables and associated commentary.
  • Nowhere in the documentary is it stated or implied that Copernicus "presented the Muslim data tables in his book". That Copernicus used some of al-Battani's observations is not at all controversial, but the only ones I'm aware of are of the obliquity and eccentricity of the ecliptic, and of the coordinates of a few stars and of the solar apogee, which Copernicus cited several times in the body of his text. As far as I'm aware, none of Copernicus's tables contain data taken directly from any Islamic sources, and there are good reasons for believing that this would be unlikely.
  • Nowhere does the documentary say anything about Muslim sources' being "deductive data tables painting heliocentrism" (whatever that may mean). In fact, at 33:46 of the documentary Prof. Al-Khalili explicitly acknowledges that even after all their mathematical advances the Islamic astronomical models still suffered from the problem that they had the Sun revolving around the Earth.
The only explicit disagreement I could find between the BBC documentary and the section of the article under discussion is in the latter's final sentence. At 6:17 of the documentary Prof. Al-Khalili says that al-Battani is the only Islamic scholar Copernicus mentioned by name. But this is demonstrably erroneous. Copernicus explicitly mentioned ibn-Rushd (Averroes) in Chapter 10 of book 1 of De Revolutionibus, and explicitly cited al-Zarqali (Arzachel) several times (in chapter 16 of book 3, p.87 verso, for example) as the source of some observations he made use of.
David Wilson (talk · cont) 05:47, 10 February 2013 (UTC)
Thanks for the info. On the issue of who's who, well, they're all anons so who kows. I was objecting to "but in reality, he owes almost nothing to ancient sources" which was put in [3] by Do you think that's different to 84.188.x, above? William M. Connolley (talk) 17:18, 10 February 2013 (UTC)
No, I'm (reasonably) sure the edits from the IP and the IPs 84.xx above are all by the same person. But the edit your link points to isn't the one that "put in" the text about owing nothing to ancient sources. That was originally done by these earlier edits from the IP The edit your link points to was just a straightforward reversion from IP of your preceding reversion, which had not only reverted the edits from IP but also removed the youtube links to the BBC documentary the editor from IP had just inserted. From what that editor says above, he or she doesn't seem to care about the former, which means that in the reversion your link points to he was just lazily using the "undo" button rather than merely reinserting his youtube links.
David Wilson (talk · cont) 21:11, 10 February 2013 (UTC)

The number of planets in the Copernican system[edit]

The intro currently says: "Earth is one of seven ordered planets in a solar system circling a stationary Sun". The diagram from De revolutionibus shows six planets plus the moon which is not usually considered a planet and is shown in the diagram circling the Earth. Would it be better to say "Earth is circled by the moon and is one of six ordered planets in a solar system circling a stationary Sun". Rjm at sleepers (talk) 07:24, 1 July 2014 (UTC)

I think it would be preferable to omit the number altogether. In this context the word "planet" is problematically ambiguous: Does it signify the concept held by Copernicus and his contemporaries, to whom it included the Moon, or does it signify the modern concept, which excludes the Moon? Whichever of the two numbers we were to choose, we should probably add an explanatory footnote for those readers who might be confused or irritated by the choice. I would be inclined to simply replace the sentence with something like "Earth is one of several planets revolving around a stationary Sun."
David Wilson (talk · cont) 13:44, 1 July 2014 (UTC)
That works for me except that the Copernican model also makes the order of the planets significant (in increasing distance from the Sun). How about "Earth is one of several planets revolving around a stationary Sun in a determined order." Rjm at sleepers (talk) 13:58, 1 July 2014 (UTC)
Sounds good to me.
David Wilson (talk · cont) 14:01, 1 July 2014 (UTC)
No other comments, so I'll make the change Rjm at sleepers (talk) 05:37, 2 July 2014 (UTC)

Copernicus's source of knowledge about Aristarchus[edit]

A recent valuable edit (thank you, editor Piledhighanddeep) inserted a citation to this interesting, and clearly reliable, source at the end of the following passage in the lead:

As a university-trained Catholic priest dedicated to astronomy, Copernicus was acquainted with the heliocentric theory proposed by the ancient Greek Aristarchus.

However, according to the source, current scholarly opinion is that Copernicus most likely obtained his knowledge about Aristarchus from a copy of Aetius's Opinions of the philosophers (then erroneously attributed to Plutarch), and that the earliest copy of this source which would have been available to Copernicus was in a Greek edition of Plutarch's works published in 1509. Since Copernicus's university training ended in 1503, its mention in the first clause of the above-quoted passage is misleading and entirely gratuitous. I have therefore amended this passsage so that it accurately reflects what is in the cited source.
David Wilson (talk · cont) 00:40, 13 January 2015 (UTC)

Even today, very little is known of Aristarchus's heliocentric opinions. — Preceding unsigned comment added by (talk) 11:33, 4 March 2015 (UTC)
When Martianus Capella's system came to the notice of Copernicus, it is hard to say. Capella's book was published in 1499. Capella's system was partly heliocentric, but not heliostatic. — Preceding unsigned comment added by (talk) 11:39, 4 March 2015 (UTC)
I think that Capella was mentioned by Copernicus in Book 1 in 1543. — Preceding unsigned comment added by (talk) 11:49, 4 March 2015 (UTC)
Plutarch might have come to the notice of Copenicus at some point. — Preceding unsigned comment added by (talk) 11:56, 4 March 2015 (UTC)


The article says that Copernicus might have been reluctant to quote pre-Christian sources. Copernicus seems to have mentioned Cicero, who died in 43 B.C. In general, it is a waste of time speculating about the secret motives of others. — Preceding unsigned comment added by (talk) 09:21, 6 May 2015 (UTC)

In his "Dialogue", Galileo was only too glad to mention the "Pythagorean opinion that the earth moves". He must have known that Pythagoras was pre-Christian. — Preceding unsigned comment added by (talk) 12:01, 6 May 2015 (UTC)