Greek Astronomy: The First “Scientific Revolution”

1. Greek Astronomy:The First “Scientific Revolution”

2. Athens, ca. 400 BC

4. Puzzlah #20 Why might the Greeks have been more dependent on astronomy than a tropical culture like the Maya? (A) More extended empire to keep coordinated (B) Navigation needed for seafaring (C) Clear weather presented more astronomical phenomena that demanded explanations (D) More extremes in weather require better calendars

5. Temple of Poseidon, Sounion

6. Gateway, Citadel of Mycenae

7. Parthenon, Athens

8. Dolphins & Lions of Delos

9. The School of Athens (Raphael)

10. 800 Years of Greek Astronomy

11. Greek Astronomical Timeline to 250 BC

12. Greek Astronomical Timeline to 250 BC Rejects mythological/supernatural explanations of nature

13. Greek Astronomical Timeline to 250 BC Atomic theory. Plurality of worlds. Infinite universe.

14. Greek Astronomical Timeline to 250 BC Physics, biology, astronomy.

15. Greek Astronomical Timeline to 250 BC Physics, biology, astronomy. Mostly erroneous

16. Greek Astronomical Timeline to 250 BC

17. Greek Astronomical Timeline 250 BC – 150 AD

18. First proved for all right triangles by Pythagoras, ca. 530 BC

19. “Irrational numbers” – discovered by Pythagoreans Square root (2) = 1.41421356... Cannot be expressed as the ratio of ANY two whole numbers (“rational” numbers). There is an infinity of rational numbers, but the square root of 2 is NOT among them. “Rational” numbers: 2, 5, 2/3, 3/2, 17/16, 129/97, 1489001/747253, .......

20. Impact of Mathematical Success on Greek Thinking Applied mathematical logic to thinking in other areas leading to "rational thinking" Preference for making deductions about nature from axioms or abstract principles Theirscience based largely on non-empirical premises Disdained making experiments Great progress in some areas, but overall success circumscribed by these biases

21. Impact of Mathematical Success on Greek Thinking Applied mathematical logic to thinking in other areas leading to "rational thinking" Preference for making deductions about nature from axioms or abstract principles Theirscience based largely on non-empirical premises Disdained making experiments Great progress in some areas, but overall success circumscribed by these biases x

22. Puzzlah # 21 You have two objects, A and B, both of which are the same shape. B weighs twice as much as A. You drop both simultaneously from a height of 3 feet. What happens? (A) A (the lighter object) hits the ground first. (B) B (the heavier object) hits the ground first. (C) They hit at the same time.

23. Greek Astronomy: Great!Rational, mathematical, logical, mostly empirical • Knew shape and size of Earth and Moon • Understood origin of lunar phases • Understood origin of eclipses • Detected (Hipparchos) polar precession • Realized (Aristarchus) that Sun is much more distant (& therefore larger) than Moon • Constructed first cosmological models that reproduced the data

24. Greek Astronomy: Spherical Shape of Earth • Curvature of ocean horizon • Different stars @ different latitudes • Different length of day @ ““ • Circular Earth shadow during lunar eclipses • Shadow lengths differ at different latitudes and can be used to measure the diameter of Earth (Eratosthenes)

25. Lunar eclipse

26. Eratosthenes and the shape and size of Earth Syene Alexandria Sun at noon, June 21: overhead at Syene, but not at Alexandria

27. Eratosthenes Method (200 BC) Apply plane geometry: Measure d, H, S. The two (approximate) triangles are congruent . This means that S/H = d/R so R = dH/S Eratosthenes answer: R = 4025 miles True value: R = 3950 miles S Alexandria H Syene

28. Hipparchos, ca 150 BC Star catalogs Magnitude system Precession Planetary data

29. Aristarchus’ Heliocentric Cosmology (ca. 250 BC)

30. Ultimate Greek Cosmology • Cosmic bodies are inanimate, physical objects, not supernatural beings • Model must explain their known motions • Spherical Earth at center of universe (a “corrupt” region) • “Superlunary” region pure, eternal, unchanging • Only purely circular (“perfect”) motions allowed • Earth is stationary;universerevolves once per day around the Earth

31. Summary of easily visible motions of celestial objects:Acceptable model must reproduce ALL

32. Summary of easily visible motions of celestial objects: Acceptable model must reproduce ALL = 'Retrograde motion"

33. “Retrograde Motion” of Mars

34. Universe of Nested Spheres

35. Early Greek Model: geocentric, nested, rotating spheres

36. Early Greek Model: geocentric, nested, rotating spheres Does this seem archaic, backward, naive, dumb?

37. Well, try this: A Traditional “Projective” Cosmology (Indian)

38. Ptolemy (ca. 130 AD): constructs ultimate Greek cosmological model

39. Ptolemy’s Geocentric Universe "Epicycle" Center of Universe

40. Epicycles are needed in a geocentric model to produce retrograde motion

41. Ptolemy: how epicycles produce retrograde motion

42. Puzzlah #22 Ptolemy's geocentric model for the solar system may have been wrong, but it was scientific. It made definite predictions, for example about phases shown by Venus in a telescope. In the model, when should Venus show a "gibbous" phase? A) Once per Earth year B) About half the time C) Once per epicyclic rotation D) Never n.b.: "gibbous" means more than half-full but less than full

43. The Dark Ages

47. Reconstruction of Acropolis, Athens

49. Greek Astronomy: Moon & Sun • Understood origin of lunar phases • Understood origin of eclipses • Detected (Hipparchos) polar precession • Realized (Aristarchus) that Sun is much more distant (& therefore larger) than Moon

50. Time-lapse video of one “lunation”