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CLA203 Exam Review.docx

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Jonathan Tracy

CLA203 Exam Review Names and TermsAristarchus of Samos ca 280 BCE pupil of the wandering philosopher Straton of Lampsacus suggested that the diameter of the earths orbit round the sun bears the same proportionto the distance of the fixed stars as the centre of the sphere bears to its surfaceimplies that the sphere of the fixed stars is infiniteinformation concerning his heliocentric theory is secondhand only work that has been preserved is the short treatise On the Sizes and Distances of the Sun and the Moon but contains no hint of his heliocentric theory Archimedes refers to this theory in his work The SandReckonersays Aristarchus brings about a book of certain hypotheses in which in follows from what is assumed that the universe is many times larger than what is to be believed to be at the present time of Archimedes writing fixed stars and sun remained unmovedthe earth is borne around the on the circumference of a circlesphere of the fixed stars situated at about the same centre as the sun is so great that the circle in which he hypothesizes that the earth revolves bears such a proportion to the distance of the fixed stars as the centre of the sphere to its surface meant that the sphere of the fixed stars is immeasurably greater than the sphere of the earths orbit round the sun still holds that sphere of fixed stars is unmoved and only the earth rotates on its axis maintained that earth and other planets revolved around sun NOT the earthhis originality lies here in making the sun the centre of the entire system theory able to explain the movements of the sun moon and planets on a unitary assumptionEudoxus had to use 8 separate spheres in his theory to explain these movements most likely that Aristarchus adopted these premises based on assumptions with any actual proof On the Sizes and Distances of the Sun and the Mooninterested in measuring the relative distances betweensizes of the earth sunmoonduring the phase of halfmoon the angle sunmoonearth is at 90 degrees could calculate the proportions of all sides of the earthmoonsun triangle used Pythagorean Theorem with trianglesmeasurements were wrong but close moonearthsun at 87 degrees correct answer 8951 calculated the earth and suns radius in approximate termsearth 3x that of moonsun 19x that of moonEratosthenes and his calculation of the earths circumference as 250 000 stades length of stadiums at the time calculated the size of the moon relative to the earth by observation of the moons position in the sky before and after a lunar eclipse was interested in solving the geometrical problems that the question presented absence of stellar parallax in Aristarchus heliocentric theorysaw this as not a problem because the stars were so far away from earth didnt attempt to prove this distanceif stars area at an infinite distance then no stellar parallax can be observed brought astronomers attention to a carefully worked out set of interrelated assumptions Seleucus of Seleucia the only astronomer in antiquity which we know of who adopted this heliocentric theory of Aristarchus reasons for rejectionsome rejected this idea based on religious groundsthe notion of the earth as the centre of the universe reflected the Greeks conception of the sacredness of the earth herself Cleanthes an early Stoic writer thought that the Greeks ought to have Aristarchus of Samos indicted on charge of impiety just as Anaxagoras was although his trial was an attempt to get to Pericles Plutarch On the Face of the Moondoctrine was seen to be open to grave astronomical and physical objections 1 Aristotelian argument from natural movements heavy objects naturally travel towards the centre of the earthassuming this law applies to heavy objects wherever they may be the centre of the earth may be presumed to coincide with the centre of gravity for the entire universe once a heavy object reaches its natural place it comes to rest apply this to the earth as a whole and we arrive at the conclusion that the earth is at rest at the centre of the universe and could not be moved except by some force sufficient enough to overcome its natural tendency fraught with difficulties itself if all heavy objects move towards the same place how are the movements of the heavenly bodies to be explained2 Arguments based on observations of objects moving through airif the earth rotates on its axis or is subject to any movement this should have a sensible effect of the movement of objects through the airthe clouds could never achieve any easterly movement for the earth would forestall themPtolemy solid bodies moving through the air should yield evidence of the earths rotation Almagest I chapter 73 Argument presented by the absence of Stellar Parallaxwhy were there no variations in the positions of the stars when observed form different points on the earths surfaceassumption that the sphere of the fixed stars is incomparably greater than the earth geocentric task is much easier to make than that of the heliocentric theorists that the sphere of the fixed stars is incomparably greater than the sphere bounded by the earths orbit round the sunChrysippus of Soli ca 280207 BCE one of the 3 developers of Stoicism50 years he junior of both Zeno of Citium and Cleanthes of Assus the other 2 founders of Stoicism worked chiefly in Athens responsible for many of the detailed doctrines and arguments that helped to consolidate the system against the criticism of its opponents
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