1. Greek Astronomy

2. Ancient View of the Cosmos  Universe is 2-D  All celestial objects attached to a sphere.  Celestial Sphere is close  Climb a high mountain and touch the sky  Celestial objects are self-luminous  Earth is the center of the universe  Objects move on perfect circles

3. Pre-disposition for success  Not Fatalists like Babylonians  Greeks had a curiosity about nature  Model builders

4. Lunar Phases and Eclipses Two important changes in thought needed  Universe is three dimensional  Some celestial objects are dark

5. Lunar Phases Phases

6. New MoonFull Moon 1 st Quarter

7. Earth (12,756 km) Moon (3476 km)

8. Lunar Eclipses Sun Earth Moon umbra penumbra

9. Lunar Eclipses b Eclipse shadow is always a section of a circle b Earth must be a sphere b Color of the eclipsed moon

10. Solar Eclipses

11. Total Solar Eclipse

12. Equator North Pole Eratosthenes Sun’s Rays Syene Alexandria 7° Video

13. Eratosthenes a 7° is about 1/50 th of a circle a Alexandria and Syene are separated by 800 km  That 800 km must be 1/50 th the circumference of the Earth  Earth Circumference = 800*50 = 40,000 km  Accepted value is 40,074 km

14. Relative sizes and distances  By 350 BC Greek Natural Philosophers knew the relative diameters and distances of the Sun, Moon, and Earth.  The Sun was very large and very far away and the Earth was bigger than the Moon.

15. Cosmologies  Heliocentric Model  Aristarchus of Samos

16. Cosmologies  Geocentric Model  Aristotle 350 BC

17. Stationary Earth  Earth is heavy  Easier to imagine the sky can move  It looks like the sky is moving  We have no sensation of our motion  Rotating Earth would make objects fly off of the surface  Stellar Parallax

18. Stellar Parallax  Hipparchus 150 BC Sun January June

19. Why did Hipparchus fail to observe Stellar Parallax? 10 1.He only looked at bright stars. 2.He was a poor observer. 3.The stars are too far away. 4.The Earth does not orbit the Sun.

20. Aristotelian Universe Terrestrial Realm Earth and Water tend to sink  Composition predicts motion natural tendencies  Overall tendency to seek rest  Objects following tendencies require no force  Objects are corruptible (changing) Fire and Air tend to rise

21. Aristotelian Universe Celestial Realm  Celestial Objects composed of Aether Self luminous but does not consume  Motion is constant, circular  Objects are incorruptible (not changing) Meteors and comets were phenomena of the Earth’s atmosphere

23. Link

24. Claudius Ptolemy (150 AD)  Accounted for retrograde motion within the confines of the Geocentric Model

25. The Sun and Moon Earth Moon

26. The Planets Earth Planet Epicycle Deferent Link

27. Retrograde Loop in Ptolemy’s System

28. Ptolemaic Universe

29. John Milton, Paradise Lost With Centric and Eccentric scribl'd o're, Cycle and Epicycle, Orb in Orb

30. Astronomy in the Dark Ages  Fall of Rome  Greek knowledge went to Islam  Alexandrian library destroyed  Universal Illiteracy  No mass communications  Villages were isolated  Thomas Aquinas  Giordano Bruno

31. End of Section