Astr. 101 Notes 2

Astr. 101 Notes 2 - -ancient Greeks knew the Earth was...

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-ancient Greeks knew the Earth was round-lunar eclipses always show the Earth’s round shadow on the Moon; the only shape that casts a circular shadow from any angle is a sphere; Columbus and his sailors knew the Earth was round (but Columbus thought the Earth was smaller) -Eratosthenes measured Earth’s diameter in 200 BCE -Aristarchus measured distances to the Sun and Moon in 280 BCE; by measuring 87 degrees he thought the Earth/ Sun distance was 20 times the Earth/ Moon distance (actually about 390 times); estimated Earth’s diameter was 3 times Moon’s diameter by timing how long it took the Moon to cross the Earth’s shadow during a lunar eclipse (actual size 3.7 times); used similar angular size of Moon and Sun and Earth/ Sun and Earth/ Moon distance to estimate size of sun as 9x10^4 km -how the ancient Greeks explained planetary motion philosophically: planets=wanderers, underpinnings of Greek geocentric model (Earth at center of universe, heavens must be “perfect”, heavenly objects are perfect spheres moving in perfect circles)
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This note was uploaded on 05/13/2011 for the course ASTR 101 taught by Professor Christiansen during the Spring '08 term at UNC.

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Astr. 101 Notes 2 - -ancient Greeks knew the Earth was...

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