Download Early Views

Greek Principles of Understanding Nature
• Nature can be understood, not just random
events controlled by whims of some gods
• Diverse behavior in nature held together by
underlying patterns
How
interesting!!
Euclid (600 BC)
• Where he was ‘wrong’
– Earth is a flat, rotating disc
– Water is basic material; all matter comes from water
• Where he was ‘right’
– Predicted solar eclipses
– Moon shines because of sun’s reflection
– All universe understandable by ordinary reasoning
Pythagoras (530 BC)
• First to suggest Earth is a sphere
• Early advocate for geocentric solar system
– Earth at center, surrounded by concentric,
rotating, transparent spheres
– Bodies attached to spheres in order: Moon,
Mercury, Venus, Sun, Jupiter, Saturn, and stars
Greek cosmology after Pythagoras
How did they know the difference between stars and planets?
Planets were the wanderers.
Problem with retrograde motion of planets occasional backward motion of seen from Earth
Eudoxus (370 BC)
• Introduced more than just 7 spheres
• Suggested 27, then 55 spheres to
explain cycles and epicycles
Aristotle (340 BC)
• Strong advocate for geocentric view
• Developed system of scientific reasoning
• Four ‘proofs’ why Earth is a sphere
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Symmetry - Sphere is perfect shape
Pressure - Pieces of Earth fall naturally to the center, pressing
it to a spherical shape (circular logic)
Shadow - During eclipse Earth’s shadow always circular
North Star - North star gets higher in sky the further north
one goes
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LA
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Seattle
LA
North
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Seattle
LA
North
Aristarchus (240 BC)
• Spinning or rotating of Earth on its axis
accounts for daily motion of stars
• Earth moves or revolves around the sun in
yearly orbit
• Had it right 200 BC, but ideas did not catch on!
Eratosthenes (235 BC)
Calculated Earth’s radius to within 2% - maybe.
Uncertainty about unit of length (stadia) he used.
Ptolemy (AD 120)
• More elaborate schemes of epicycles to
explain observations
• No significant changes for next 1300 years
• Ptolemaic synonymous with
geocentric view of solar system
Copernicus (1500’s)
Major Break with Past!
• Beginning of end of geocentric view
• Advocated heliocentric view, but had no proof
– Sun at center of solar system
– Planets in order outward from Sun: Mercury, Venus, Earth
(moon), Mars, Jupiter, Saturn
• Ideas not accepted in his lifetime (died 1543)
• Resisted by church
• Copernican synonymous with heliocentric view of
solar system
Sources of web images (1/2):
Euclid
http://www.storyofmathematics.com/hellenistic_euclid.html
Pythagoras
http://www.sciencephoto.com/media/227667/enlarge
Greek cosmology
http://hendrix2.uoregon.edu/~imamura/123/lecture-5/lecture-5.html
Discovery of Pluto
http://en.wikipedia.org/wiki/Pluto
Mars retrograde
http://apod.nasa.gov/apod/ap080511.html
http://www.sjaa.net/eph/0711/d.html
Eudoxus
http://www.crystalinks.com/eudoxus.html
Aristotle
http://www.catholiceducation.org/articles/apologetics/ap0016.html
Source of web images (2/2):
Aristarchus
http://www.nndb.com/people/756/000096468/
Eratosthenes
http://www.eg.bucknell.edu/physics/astronomy/astr101/specials/eratosthenes.html
Ptolemy
http://en.wikipedia.org/wiki/Ptolemy
http://abyss.uoregon.edu/~js/ast123/lectures/lec02.html
Copernicus
http://en.wikipedia.org/wiki/Nicolaus_Copernicus