“Reserve your right to think, for even to think wrongly is better

1. “Reserve your right to think, for even to think wrongly is better than not to think at all. To teach superstitions as truth is a most terrible thing.” - Hypatia

2. Bit of Administration …. • Reading • Bless, Chapters 3-6 • BDSV pp. 56-73 • Portfolio Assignment • The goal of your portfolio is for you to demonstrate your achievement of: Knowing the sky and the Solar System as a part of your environment to which you are connected – physically, historically, and culturally/personally. • The portfolio should include 5 documents demonstrating your learning in these dimensions: • 1) A cultural connection to the sky; you are encouraged to explore non-European cultures. • 2) A connection of Newton’s laws of motion and/or gravity to experiences in your life. • 3) A connection of the physics of light to experiences in your life. • 4) A connection of the Sun’s energy to your life, or the impact of the Second Law of Thermodynamics. • 5) Your connection to the larger evolutionary processes of the Earth and Solar System. • Due April 28; you are encouraged to submit your first documents for review and grading before then in order to develop your skills in advance of doing the entire portfolio.

3. Earliest Civilizations

4. Early Greek Astronomy • Plato 400 BC • Geometric Ideals Underly Reality • Uniform Circular Motion • Circular Motion at Constant Speed • “No beginning, no end, no change” • Construct a geometric representation of celestial motions using only combinations of uniform circular motions about the central fixed earth • Senses are Imperfect and Unreliable • Observation is not important - reason reigns supreme • Qualitative agreement is acceptable

5. Early Greek Astronomy • Eudoxus and Calippus 400 BC

6. Right Reasoning, Right Conclusion! Wrong Reasoning, Right Conclusion! Wrong Reasoning, Wrong Conclusion! Right Reasoning, Wrong Conclusion! Early Greek Astronomy • Aristotle 350 BC • Lunar Phases and Eclipses • Argued that Sun was further than the moon • Eclipses • Slower motion in the sky • Argued that Moon shines by reflected light from Sun • Intellectual leap toward relationships that are independent of Earth • Spherical Earth • Shadow is round during lunar eclipses • Travel in latitude changes the positions of the stars • Elephants were found both to the east in India and to the west in Morocco • Only spherical shape would allow motion to the center to be straight down • Motion of Earth • Realized that daily motion could be either earth or celestial sphere spinning • Considered heliocentric universe, but rejected because no parallax was seen • Cosmology of the Spheres

7. Early Greek Astronomy • Aristotle 350 BC • Chemistry • Earth, Air, Fire, Water - the stuff of the human world • Quintessence - the stuff of the celestial bodies • Physics • The universe as a machine • All vertical motion driven by inclination to natural places • The natural place of Earth was toward the center of the Universe/Earth • First theory of gravity! • Encyclopedic Treatises on Nearly Every Field For 2000 years the Universe was Aristotelian (though primary impact was after 1200 AD)

8. The Alexandrian School • Located in Egypt, but center of Greek culture after 330 BC • Conquests of Babylonia by Alexander the Great brought rich observational data

9. The Alexandrian School • Aristarchus of Samos 300 BC "You King Gelon are aware the 'universe' is the name given by most astronomers to the sphere the center of which is the center of the Earth, while its radius is equal to the straight line between the center of the Sun and the center of the Earth. This is the common account as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the 'universe' just mentioned. His hypotheses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun on the circumference of a circle, the Sun lying in the middle of the orbit, and that the sphere of fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the Earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface." • Archimedes

10. The Alexandrian School • Aristarchus of Samos 300 BC • Relative Distances of Moon and Sun

11. M EM ES = cos MES S E Earth Sun

12. Earth Sun M S E The Alexandrian School • Aristarchus of Samos 300 BC • Relative Distances of Moon and Sun • Requires measuring the angle MES • Suggested measuring time from first quarter to third quarter and time from third quarter to first quarter, then taking the ratio • Used 87o with no mention of origin • Found that the Sun is 20x further than the Moon • But in fact ….

13. Sun Earth The Alexandrian School • Aristarchus of Samos 300 BC • Relative Distances of Moon and Sun • Requires measuring the angle MES • Suggested measuring time from first quarter to third quarter and time from third quarter to first quarter, then taking the ratio • Used 87o with no mention of origin • Found that the Sun is 20x further than the Moon • Measurement of angle MES is impossible; Sun is 400x further than the Moon

14. The Alexandrian School • Aristarchus of Samos 300 BC • Relative Sizes of Moon and Sun

15. Earth 1 20 The Alexandrian School • Aristarchus of Samos 300 BC • Relative Sizes of Moon and Sun • Sun and Moon are same angle in the sky (0.5o) • Sun is 20x further away than the Moon • Sun must be 20x larger than the Moon

16. The Alexandrian School • Aristarchus of Samos 300 BC • Relative Sizes of Earth, Moon and Sun

17. 3 2 1 Time 1 0 hr Time 2 1 hr Time 3 3 hr Earth Earth’s Shadow is 3x Diameter of Moon

18. The Alexandrian School • Found that Sun is 6-7x larger than the Earth, compared to 109x • The Sun is larger than the Earth! • Led him to suggest a Sun-centered (“heliocentric”) universe • Aristarchus of Samos 300 BC • Relative Sizes of Earth, Moon and Sun Earth

19. The Alexandrian School • Found that Sun is 6-7x larger than the Earth, compared to 109x • The Sun is larger than the Earth! • Led him to suggest a Sun-centered (“heliocentric”) universe • "[Cleanthes, a contemporary of Aristarchus] thought it was the duty of the Greeks to indict • Aristarchus of Samos on the charge of impiety for putting in motion the Hearth of the • universe [i.e. the earth], . . . supposing the heaven to remain at rest and the earth to • revolve in an oblique circle, while it rotates, at the same time, about its own axis." • Plutarch • Aristarchus of Samos 300 BC • Relative Sizes of Earth, Moon and Sun

20. The Alexandrian School • Eratosthenes 200 BC • The Size of the Earth • Note that all of Aristarchus’ results are relative sizes

21. From Sun Light rays from very distant objects arrive at every point on Earth from the same direction! From Sun NY Earth HK From Sun

22. From Sun From Sun 7 o Alexandria 7 o Syene Distance around Earth = 360o/7o x Distance Syene to Alexandria = 50 x 5000 stades !

23. The Alexandrian School • The Size of the Universe, circa 200 BC • Earth’s Diameter 13,000 km 12,756 km • Moon’s Diameter 4,300 3476 • Sun’s Diameter 9 x 104 1.39 x 106 • Earth-Moon Distance 4 x 105 3.84 x 105 • Earth-Sun Distance 107 1.50 x 108