Lecture2 Early History

Lecture2 Early History - Early History of Cosmology 1/22/09...

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1/22/09 Astronomy 309R - Spring 2009 1 Early History of Cosmology
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1/22/09 Astronomy 309R - Spring 2009 2 Google maps Athens Alexandria
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1/22/09 Astronomy 309R - Spring 2009 3 • Pythagoras (about 582 - 507 B.C.) – Geometric harmony in the universe: notion that nature (e.g., the motion of celestial bodies) is constructed to follow simple numerical relations: planets move on crystalline spheres and emit sounds that we are unable to hear. Sizes of the spheres are in harmonic proportion. • Plato (about 427 - 347 B.C., Athens, founded the first university) – What we see may be but a shadow of the reality that is composed of abstract “forms.” The reality can be reached by an intelligent mind. – Planets correspond to perfect solids (?)
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1/22/09 Astronomy 309R - Spring 2009 4 Greek Cosmology (Starting ~ 600 B.C.) Athens and Alexandria: democracy, philosophy, intellectual speculation, mutual disagreement, debate Rejection of mythical and magical explanations in favor of rational and mechanical explanations Utilization of generalizations and abstract and mathematical notions to contemplate the universe Attempts to identify basic ingredients that make the universe: water? air? atoms? fire? earth? ether ? atoms ? Attempted to define the ultimate nature of matter: atoms in relation to each other? Attempts to define motion and understand its origin First measurements of distances in the solar system
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1/22/09 Astronomy 309R - Spring 2009 5 What did a Hellenistic naked-eye sky watcher have to explain? • The stars, moving daily around the celestial poles. Celestial poles = points on the sky just above the North and South pole • The sun, moving daily around the celestial poles, and drifting annually eastward along the ecliptic, faster in the winter, slower in the summer. Ecliptic = plane containing the earth’s orbit around the sun; path of the sun on the sky relative to the stars. • The moon, moving daily around the celestial poles, and drifting monthly eastward near the ecliptic. • The planets, moving daily around the celestial poles, drifting eastward at different rates with occasional westward “retrograde motion,” are faintest when near the sun. http://mars.jpl.nasa.gov/allabout/nightsky/nightsky04-2003animation.html
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1/22/09 Astronomy 309R - Spring 2009 6 • Eudoxus of Cnidus (about 408-355 B.C., Athens, student of Plato) – Planets move on concentric spheres pivoted to each other on the poles, separate sphere (or a number of connected spheres) for each planet: altogether 27 spheres: 1 for the stars, 3 each for the sun and the moon, and 4 each for 5 planets (Mercury, Venus, Mars, Jupiter, Saturn) Figure by Prof. Richard Pogge, Ohio State University http://brunelleschi.imss.fi.it/museum/esim.asp?c=500052
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1/22/09 Astronomy 309R - Spring 2009 7 Aristotle (384-322 B.C., Athens) – Student of Plato, pioneer of logic, the tutor of Alexander the Great – Believed that the earth is a sphere because the shadow of the earth on the
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This note was uploaded on 09/14/2009 for the course AST 309 taught by Professor Johnlacy during the Spring '08 term at University of Texas.

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Lecture2 Early History - Early History of Cosmology 1/22/09...

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