Age of aquarius when the sun on the spring equinox

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year. (“Age of Aquarius”: when the sun on the spring Equinox reaches the Aquarius constellation). 2. All star coordinates shift .014 degree East per year. (By 2200, Polaris will no longer mark the NCP; aka “precession of the Pole star”) * Animation: Precession of the Pole Star 8. Eratosthenes (~276-195 BC) - Estimated Earth’s circumference by measuring the length of the shadow cast by a stick.
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9. Apollonius (~262-190 BC) Devised the epicycle model of constant, circular planetary motion, which explains: - Retrograde motion - Changing angular speeds (planet’s tangential component can vary) - Changing brightness (planet’s distance can vary) This model was in use for nearly 300 years.
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Animation: The epicycle model 1. Claudius Ptolemy (~85-161 AD) - Author of Mathematical Treatise (~150 AD), a.k.a The Almagest (“The Great Treatise”), the definitive astronomy textbook for 1400 years. - It presents the lost works of the ancient Greeks, a star catalogue, and the Ptolemaic model of planetary motion. 2. The Ptolemaic Model Ptolemy modified the epicycle model to improve its accuracy: - He displaced Earth from the center. - He added the equant point, which forces the epicycle to have non-constant motion. Animation… 3. Ptolemy further modified his model to explain the different paths of the inner vs outer
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planets Applet: Ptolemaic motion of an inner planet Applet: Ptolemaic motion of an outer planet 4. Ptolemy’s order of the planets a. Moon is closest (since it’s never eclipsed by a planet). b. 5 visible planets, from fastest to slowest (sun between Venus& Mars to separate inner vs outer types of motion). c. Sun is on the center , not the earth d. The fixed stars.
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5. By assuming his order of the planets was correct with no space between adjacent epicycles, Ptolemy estimated the size of the Universe to be ~20,000 Earth radii (actual: 260,000). Despite the error, this proved the enormous distance to the stars Mercury’s min distance = Moon’s max distance Chapter 4 1. Astronomy in the Middle Ages (~5 th -15 th C AD) In the Dark Ages (5 th -7 th C), knowledge of Astronomy declined as the church became more involved in State affairs: - Study of the sky not emphasized in the Bible. - Rejection of Ancient Greek “pagan” ideas. - Loss of Ancient Greek texts (Latin became the official language of scholarship) 2. Between the 9-12 th C, Islamic scholars continued from where the Ancient Greeks left off: - The Qur’an encourages knowledge of the sky for time-keeping - Interactions with Greek refugee scholars led to translations of the ancient Greek texts into Arabic (e.g. Almagest). 3. - New star catalogues were created in which the stars were renamed with Arabic descriptions - When the Arabic catalogues later made their way into Europe, the Arabic star names persisted (still used today).
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Buridan dismantled the Aristotelian argument that an arrow’s motion proves that Earth is fixed. His theory of impetus (momentum) shows: - A Fixed Earth and a moving Earth re equivalent from our perspective on Earth.
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  • Fall '11
  • RobinMetcalfe

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