Chapter 3 - Ancient Astronomy Many cultures throughout the...

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Ancient Astronomy Many cultures throughout the world practiced astronomy. Over a period of time, they would notice the cyclic motions of: Sun Moon planets celestial sphere (stars)
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Why did they do it? to keep time for agricultural purposes for religious purposes As far as we can tell, none of these ancient cultures tried to build a physical model based on their observations. Instead, they created myths to explain the motions of the objects in the sky.
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Eratosthenes (276 - 195 BC) He measured the circumference of the Earth. The Sun is at the zenith in the city of Syene at noon on the summer solstice. But at the same time in Alexandria, it is 7 ° from the zenith. Eratosthenes inferred that Alexandria was 7 ° of latitude north of Syene. The distance between the two cities is 7/360 times the Earth’s circumference. His result of 42,000 km is very close to the right number: 40,000 km.
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Claudius Ptolemy (AD 100-170) Almagest star catalogue instruments motions & model of planets, Sun, Moon Made first scientific model of universe, Earth was the center His model fit the data, made accurate predictions!
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Ptolemy’s Geocentric Model Earth is at center Sun orbits Earth Planets orbit on small circles whose centers orbit the Earth on larger circles [the small circles are called epicycles ]
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Ptolemy’s Geocentric Model This explained retrograde motion Inferior planet epicycles were fixed to the Earth-Sun line This explained why Mercury & Venus never strayed far from the Sun!
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This note was uploaded on 08/16/2011 for the course AST 2002 taught by Professor Britt during the Spring '08 term at University of Central Florida.

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Chapter 3 - Ancient Astronomy Many cultures throughout the...

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