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lways appear to move at uniform speed all other locations would see non uniform speed as on the earth by using an equant ptolemy claimed to keep motion which was uniform and circular although it departed from the platonic ideal of uniform circular motion the resultant system which eventually came to be widely accepted in the west seems unwieldy to modern astronomers each planet required an epicycle revolving on a deferent offset by an equant which was different for each planet it predicted various celestial motions including the beginning and end of retrograde motion to within a maximum error of 10 degrees considerably better than without the equant the model with epicycles is in fact a relatively accurate model of an elliptical orbit with low eccentricity the ellipse shape does not appear to a noticeable extent when the eccentricity is less than 5 but the offset distance of the center or the focus occupied by the sun is very noticeable even with low eccentricities as possessed by the planets persian and arab astronomy and geocentrism edit main articles maragheh observatory astronomy in medieval islam and islamic cosmology after the graeco arabic translation movement that included the translation of the almagest from greek to arabic muslims adopted and refined the geocentric model of ptolemy which they believed correlated with the teachings of islam 10 11 12 muslim astronomers generally accepted the ptolemaic system and the geocentric model 13 but by the 10th century texts appeared regularly whose subject matter expressed doubts concerning ptolemy shukūk 14 several muslim scholars questioned earth s apparent immobility 15 16 and centrality within the universe 17 some muslim astronomers believed that earth rotates around its axis such as abu sa id al sijzi d c 1020 18 19 according to al biruni sijzi invented an astrolabe called al zūraqī based upon a belief held by some of his contemporaries that the motion we see is due to the earth s movement and not to that of the sky 19 20 the prevalence of this belief is further confirmed by a reference from the 13th century that states according to the geometers or engineers muhandisīn the earth is in constant circular motion and what appears to be the motion of the heavens is actually due to the motion of the earth and not the stars 19 early in the 11th century alhazen wrote a scathing critique of ptolemy s model in his doubts on ptolemy c 1028 which some have interpreted to imply he was criticizing ptolemy s geocentrism 21 but most agree that he was actually criticizing the details of ptolemy s model rather than his geocentrism 22 in the 12th century arzachel departed from the ancient greek idea of uniform circular motions by hypothesizing that the planet mercury moves in an elliptic orbit 23 24 while alpetragius proposed a planetary model that abandoned the equant epicycle and eccentric mechanisms 25 though this resulted in a system that was mathematically less accurate 26 his alternative system spread through most of europe during the 13th century 27 fakhr al din al razi 1149 1209 in dealing with his conception of physics and the physical world in his matalib rejects the aristotelian and avicennian notion of the earth s centrality within the universe but instead argues that there are a thousand thousand worlds alfa alfi awalim beyond this world such that each one of those worlds be bigger and more massive than this world as well as having the like of what this world has to support his theological argument he cites the qur anic verse all praise belongs to god lord of the worlds emphasizing the term worlds 17 the maragha revolution refers to the maragha school s revolution against ptolemaic astronomy the maragha school was an astronomical tradition beginning in the maragha observatory and continuing with astronomers from the damascus mosque and samarkand observatory like their andalusian predecessors the maragha astronomers attempted to solve the equant problem the circle around whose circumference a planet or the center of an epicycle was conceived to move uniformly and produce alternative configurations to the ptolemaic model without abandoning geocentrism they were more successful than their andalusian predecessors in producing non ptolemaic configurations which eliminated the equant and eccentrics were more accurate than the ptolemaic model in numerically predicting planetary positions and were in better agreement with empirical observations 28 the most important of the maragha astronomers included mo ayyeduddin urdi d 1266 nasīr al dīn al tūsī 1201 1274 qutb al din al shirazi 1236 1311 ibn al shatir 1304 1375 ali qushji c 1474 al birjandi d 1525 and shams al din al khafri d 1550 29 however the maragha school never made the paradigm shift to heliocentrism 30 the influence of the maragha school on copernicus remains speculative since there is no documentary evidence to prove it the possibility that copernicus independently developed the tusi couple remains open since no researcher has yet demonstrated that he knew about tusi s work or that of the maragha school 30 31 ptolemaic and rival systems edit not all greeks agreed with the geocentric model the pythagorean system has already been mentioned some pythagoreans believed the earth to be one of several planets going around a central fire 32 hicetas and ecphantus two pythagoreans of the 5th century bc and heraclides ponticus in the 4th century bc believed that the earth rotated on its axis but remained at the center of the universe 33 such a system still qualifies as geocentric it was revived in the middle ages by jean buridan heraclides ponticus was once thought to have proposed that both venus and mercury went around the sun rather than the earth but it is now known that he did not 34 martianus capella definitely put mercury and venus in orbit around the sun 35 aristarchus of samos wrote a work which has not survived on heliocentrism saying that the sun was at the center of the universe while the earth and other planets revolved around it 36 his theory was not popular and he had one named follower seleucus of seleucia 37 epicurus was the most radical he correctly realized in the 4th century bc that the universe does not have any single center this theory was widely accepted by the later epicureans and was notably defended by lucretius in his poem de rerum natura 38 copernican system edit main article copernican heliocentrism in 1543 the geocentric system met its first serious challenge with the publication of copernicus de revolutionibus orbium coelestium on the revolutions of the heavenly spheres which posited that the earth and the other planets instead revolved around the sun the geocentric system was still held for many years afterwards as at the time the copernican system did not offer better predictions than the geocentric system and it posed problems for both natural philosophy and scripture the copernican system was no more accurate than ptolemy s system because it still used circular orbits this was not altered until johannes kepler postulated that they were elliptical kepler s first law of planetary motion tychonic system edit main article tychonic system in this depiction of the tychonic system the objects on blue orbits the moon and the sun revolve around the earth the objects on orange orbits mercury venus mars jupiter and saturn revolve around the sun around all is a sphere of stars which rotates tycho brahe 1545 1601 made more accurate determinations of the positions of planets and stars he sought the effect of stellar parallax which would have been empirically verifiable proof of the earth s motion around the sun predicted by the copernican model having observed no effect he rejected the idea of the earth s motion 39 consequently he introduced a new system the tychonic system in which the earth was still at the center of the universe and around it revolved the sun but all the other planets revolved around the sun in a set of epicycles his model considered both the benefits of the copernican model and the lack of evidence for the earth s motion 40 observation by galileo and abandonment of the ptolemaic model edit with the invention of the telescope in 1609 observations made by galileo galilei such as that jupiter has moons called into question some of the tenets of geocentrism but did not seriously threaten it because he observed dark spots on the moon craters he remarked that the moon was not a perfect celestial body as had been previously conceived this was the first detailed observation by telescope of the moon s imperfections which had previously been explained by aristotle as the moon being contaminated by earth and its heavier elements in contrast to the aether of the higher spheres galileo could also see the moons of jupiter which he dedicated to cosimo ii de medici and stated that they orbited around jupiter not earth 41 this was a significant claim as it would mean not only that not everything revolved around earth as stated in the ptolemaic model but also showed a secondary celestial body could orbit a moving celestial body strengthening the heliocentric argument that a moving earth could retain the moon 42 galileo s observations were verified by other astronomers of the time period who quickly adopted use of the telescope including christoph scheiner johannes kepler and giovan paulo lembo 43 in 1610 galileo galilei observed with his telescope that venus showed phases despite remaining near the sun in earth s sky first image this proved that it orbits the sun and not earth as predicted by copernican and tychonic models and disproved the ptolemaic one second image in december 1610 galileo galilei used his telescope to observe that venus showed all phases just like the moon he thought that while this observation was incompatible with the ptolemaic system it was a natural consequence of the heliocentric system however ptolemy placed venus deferent and epicycle entirely inside the sphere of the sun between the sun and mercury but this was arbitrary he could just as easily have swapped venus and mercury and put them on the other side of the sun or made any other arrangement of venus and mercury as long as they were always near a line running from the earth through the sun such as placing the center of the venus epicycle near the sun in this case if the sun is the source of all the light under the ptolemaic system if venus is between earth and the sun the phase of venus must always be crescent or all dark if venus is beyond the sun the phase of venus must always be gibbous or full but galileo saw venus at first small and full and later large and crescent this showed that with a ptolemaic cosmology the venus epicycle can be neither completely inside nor completely outside of the orbit of the sun as a result ptolemaics abandoned the idea that the epicycle of venus was completely inside the sun and later 17th century competition between astronomical cosmologies focused on variations of the tychonic or copernican systems historical positions of the roman catholic hierarchy edit the galileo affair pitted the geocentric model against the claims of galileo in regards to the theological basis for such an argument two popes addressed the question of whether the use of phenomenological language would compel one to admit an error in scripture both taught that it would not pope leo xiii wrote we have to contend against those who making an evil use of physical science minutely scrutinize the sacred book in order to detect the writers in a mistake and to take occasion to vilify its contents there can never indeed be any real discrepancy between the theologian and the physicist as long as each confines himself within his own lines and both are careful as st augustine warns us not to make rash assertions or to assert what is not known as known if dissension should arise between them here is the rule also laid down by st augustine for the theologian whatever they can really demonstrate to be true of physical nature we must show to be capable of reconciliation with our scriptures and whatever they assert in their treatises which is contrary to these scriptures of ours that is to catholic faith we must either prove it as well as we can to be entirely false or at all events we must without the smallest hesitation believe it to be so to understand how just is the rule here formulated we must remember first that the sacred writers or to speak more accurately the holy ghost who spoke by them did not intend to teach men these things that is to say the essential nature of the things of the visible universe things in no way profitable unto salvation hence they did not seek to penetrate the secrets of nature but rather described and dealt with things in more or less figurative language or in terms which were commonly used at the time and which in many instances are in daily use at this day even by the most eminent men of science ordinary speech primarily and properly describes what comes under the senses and somewhat in the same way the sacred writers as the angelic doctor also reminds us went by what sensibly appeared or put down what god speaking to men signified in the way men could understand and were accustomed to providentissimus deus 18 maurice finocchiaro author of a book on the galileo affair notes that this is a view of the relationship between biblical interpretation and scientific investigation that corresponds to the one advanced by galileo in the letter to the grand duchess christina 44 pope pius xii repeated his predecessor s teaching the first and greatest care of leo xiii was to set forth the teaching on the truth of the sacred books and to defend it from attack hence with grave words did he proclaim that there is no error whatsoever if the sacred writer speaking of things of the physical order went by what sensibly appeared as the angelic doctor says speaking either in figurative language or in terms which were commonly used at the time and which in many instances are in daily use at this day even among the most eminent men of science for the sacred writers or to speak more accurately the words are st augustine s the holy spirit who spoke by them did not intend to teach men these things that is the essential nature of the things of the universe things in no way profitable to salvation which principle will apply to cognate sciences and especially to history that is by refuting in a somewhat similar way the fallacies of the adversaries and defending the historical truth of sacred scripture from their attacks divino afflante spiritu 3 in 1664 pope alexander vii republished the index librorum prohibitorum list of prohibited books and attached the various decrees connected with those books including those concerned with heliocentrism he stated in a papal bull that his purpose in doing so was that the succession of things done from the beginning might be made known quo rei ab initio gestae series innotescat 45 th...
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