AS101 Lecture 8

AS101 Lecture 8 - AS101 Lecture 8 Logistics Pr Set 3 Due...

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AS101 Lecture 8 Logistics: • Pr. Set 3: Due Oct 5 – Make sure that you are on MasteringAstronomy! Last Lecture: • Solar Eclipses • Planetary motions • Historic development of Astronomy Today’s Lecture: • Greek astronomy • Heliocentric universe • Ptolemy, Copernicus, Brahe, Kepler Astrolabe: Star & Planet Calculator
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Contributions of Greek Astronomers
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How did we figure out the simple things? Shape of the Earth Size of the Earth
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Curiosity: Shape of the Earth A flat Earth floating on the sea inside the celestial sphere In fact, Alexander the Great believed that the edge of the world was in India but when he got there he still did not find it Homer's view of the world http://www.henry-davis.com/MAPS/Ancient%20Web%20Pages/105.html Jennifer Bower: What data do we need to test this idea?
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A suggested test Find a friend with a telephone in the Southern hemisphere and another one in Asia Ask them what the sky is like Look out the window and write down what the sky is like for you Compare Are they the same? (OK, lets leave out cloud cover, weather pattern, etc.) Thanh Vo: Why did we choose these locations?
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Ancients: The shape of the Earth Observations: • Star pattern changes from place to place • Ships and ports appear to rise from the sea • The shadow of the Earth on the Moon always look like a part of a circle The only way these three observations could be explained is if the Earth were spherical (Aristotle 384- 322 BC – Alexander the Great’s teacher)
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Ancient Mathematics & Physics Euclid of Syracuse (300B.C.) • Advanced Geometry • Wrote Euclid’s “The Elements” • Longest running textbook in history Archimedes (287-212 BC) • Laid foundations of calculus • Explained levers • Explained water flow
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How big is the Earth? It was known that on the summer solstice at noon the shadow of a rim of a well in Syene disappeared.ie. the Sun is directly overhead Eratosthenes noted that at the same time the shadow of an obelisk in Alexandra did not disappear! He measured the distance between the two cities by knowing how long it takes camel caravans to cover the distance (50 days at 100 stadia per day) From that he calculated the circumference of the Earth! 5,000 Stadia
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So, how big is the Earth? Eratosthenes (276 - 196 BC) Alexandria and Syene were 5,000 stadia apart and the shadow was 7 ° So, Circumf. Earth/5,000 = 360/7 i.e. Earth’s circumf. = 2.5 × 10 4 stadia 1stadium = 1/6 km gives very good agreement with present-day number now Aswan http://www- groups.dcs.st- and.ac.uk/~history/P ictDisplay/Eratosthen es.html
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Length of a stadium • His number for the distance between Alexandria and Syene was 800 km, a better number is 729 The measurement of the angle • He used 7 ° 12′, the better number is 7 ° 5′ The fact that Alexandria and Syene are not on the same longitude What are the possible sources of error?
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This note was uploaded on 04/14/2011 for the course ASTRO 101 taught by Professor Oppenheim during the Spring '11 term at BU.

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AS101 Lecture 8 - AS101 Lecture 8 Logistics Pr Set 3 Due...

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