Lecture2_Sept26_2007

Lecture2_Sept26_2007 - PhSc11900: Stellar Astronomy and...

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PhSc11900: Stellar Astronomy and Astrophysics Lecture 2, September 26 th 2007 Early Questions, and Answers, continued: Early Astronomy: The Greeks, 610 B.C.E – 165 C.E. cont. The Solar System is the Universe, and has the Earth at the center. Astronomical Renaissance: 1473 C.E. – 1642 C.E. The Solar System is the Universe, and has the Sun at the center. What about the Stars?: 1546 C.E. – 1840 C.E. The Milky Way is the Universe, and has the Sun at the center. The Fall of Man: 1724 C.E. – present The Universe is huge, and we occupy no special place.
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Early Astronomy: The Greeks, 610 B.C.E – 165 C.E. The Solar System is the Universe, and has the Earth at the center. Eratosthenes of Cyrene (276 B.C.E. - 194 B.C.E.) Eratosthenes measured the size of the Earth using shadows cast by the Sun during the summer solstice at noon at the cities of Syene and Alexandria. The size he derived is open to some debate because the distance between Alexandria and Syene is given in documents using a unit (the ‘stadion’) whose precise value in modern terms is unknown. Nevertheless, the best interpretation of Eratosthenes’ value of the size of the Earth is 39690 km – remarkably close to the actual value of 40008 km. This is perhaps the best early example of an observer working in a particular theoretical paradigm. Alexandria (sun 7.2º off vertical – due north of Syene) Syene (sun directly overhead) The distance between Alexandria and Syene is 7.2/360 (1/50 th ) of the circumference of the Earth
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Early Astronomy: The Greeks, 610 B.C.E – 165 C.E. The Solar System is the Universe, and has the Earth at the center. Claudius Ptolemy (85 C.E. - 165 C.E.) Ptolemy advanced and refined the geocentric ideas of Aristotle regarding the motions and perfection of heavenly bodies and their organization on celestial spheres, and the ideas of other astronomer/mathematicians of the day (notably the epicycles of Apollonius, and the observations and astronomical models of Hipparchus). In his landmark work Almagest, Ptolemy lays out a complex geometrical model of the solar system, with the Earth at the center, which uses epicycles to produce the observed retrograde motions of planets. Though notably complex in its final form, it was remarkably accurate, and an excellent predictive tool for planetary motions. This Ptolemaic cosmology held sway in western thought for the next 1500 years.
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Early Questions, and Answers: Astronomical Renaissance: 1473 C.E. – 1642 C.E. The Solar System is the Universe, and has the Sun at the center. “Real knowledge is to know the extent of one’s ignorance.” Confucius “Nothing could be more obvious than that the Earth is stable and unmoving, and that we are the center of the Universe. Modern western science takes its beginning from the denial of this common sense axiom.” Daniel L. Boorstin
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Astronomical Renaissance: 1473 C.E. – 1642 C.E. The Solar System is the Universe, and has the Sun at the center.
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This note was uploaded on 04/07/2008 for the course PHSC 119 taught by Professor Gladders during the Fall '08 term at UChicago.

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Lecture2_Sept26_2007 - PhSc11900: Stellar Astronomy and...

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