# Lecture3 - Quiz 1 Signature Course UGS 303(Fall 2009...

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9/14/09 1 The History and Philosophy of Astronomy (Lecture 3: Antiquity I) Instructor: Volker Bromm The University of Texas at Austin Department of Astronomy Signature Course UGS 303 (Fall 2009) Quiz 1: • Question: Ancient Egypt and Mesopotamia (Babylonia) were both impressive civilizations. But the level of sophistication in astronomy was much higher in Babylonia. Why is that? Answer: ! The main reason is that the Babylonians had a much more advanced system to do calculations (arithmetic with a place-value scheme, including fractions)! Only with such high-precision math can one determine celestial positions (angles on the sky) with high accuracy! Ancient Greece: The Birth of Science 6 th cent. BC: Use geometry to address celestial motions Observing the Sky: The Basic Facts Earth is a Sphere Daily motion of celestial sphere (stars) Stars don ʼ t change their relative positions Annual motion of Sun with respect to stars Moon ʼ s motion w.r.t. to Fxed stars Planets motion w.r.t. to Fxed stars weird (all with the naked eye!)

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9/14/09 2 Spherical shape of the Earth Ships at sea • Lunar eclipse: earth ʼ s shadow circular • Traveler ʼ s Tales (e.g., recorded by Herodotus) Size of the Spherical Earth Use geometry and common sense Eratosthenes (3 rd cent. BC, Alexandria) -7 o = 800 km -360 o = 40,000 km Daily motion of the stars No change in relative positions fxed stars Daily motion of the stars: Looks different in different directions! Due North Due East Due South - Circumpolar stars
9/14/09 3 Q: How to explain daily stellar motion??? Celestial sphere (contains fxed stars) Celestial equator Local Horizon (every observer has own one!) A: The Ancient Two-sphere-universe! Quick reminder: Why does concept of celestial sphere

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Lecture3 - Quiz 1 Signature Course UGS 303(Fall 2009...

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