The Egyptians through the Greeks

1. The Egyptians through the Greeks This logo denotes A102 appropriate

2. The Practical Sky • Probably before there was civilization there was a need to keep track of days • Migration of prey animals • Rutting season for domesticated animals • Agriculture: planting and harvesting (8000 years ago)‏ • The phases of the Moon, the rising position of the Sun, and prominent constellations provided clues for the time of year

3. Timeline • Dates in some cases are approximate; some civilizations achieved various milestones at later times. The dates cited are generally the earliest verifiable dates.

4. Prehistoric Civilizations • Clockwise from top: Varna 4400BC, Mesopotamia 3100 BC, Tell Hamoukar 4000BC, Tell Qaramel 9600 BC, Minos 2700 BC

5. Dangers in Interpreting Ancient Structures • We must take care not to superimpose our understanding of the sky onto ancient builders • One way to avoid this error is to look at many supposedly astronomically inspired structures • Why do you think the preferred orientation is slightly south of east? Orientation of Late Stone Age communal tombs on the Iberian peninsula. M. Hoskins

6. Egyptian Astronomers • Constructed by nomadic cattle herders • ~ 7000 years old • Covers an area of 2.9 km by 1.2 km • 10 slabs about 2.7 meters high, bovine burial mounds, and a calendar circle

7. Goseck Circle • Oldest Solar Observatory • Discovered in Germany 2002 • Bronze Age (7000 years ago) • Reconstructions on upper, middle right • Nebra disk (bottom) found nearby but not nearly so old

8. Sumerian Planosphere

9. Stonehenge

10. Solstice Sunrise at Stonehenge

11. Carhenge (not so ancient)

12. Babylon • Ziggurat (Ur, Iraq; 2000 BCE)‏ • Celestial Observatory and temple

13. Cuneiform citing lunar eclipse Centuries of recorded planetary observations

14. Thirteen Towers of Chankillo • Peru, 2300 years old • Oldest Solar Observatory in the Americas • Towers stand 6 to 13 feet, extending 1,00 feet away, marking positions of the Sun over a year • From central position the arc of the rising Sun is subtended • Ceremonial buildings in the rings Observers stood here

15. Mayan Observatories circa 900 AD El Caracol Chichen Itza

16. The Antikythera • An instrument, not an observatory • 1st Century BCE • Named for the Greek island near the shipwreck from which this was discovered, circa 1900 • A mechanical computer for celestial positions

17. Similar to Byzantine sundial calendar, 500 AD • But this is much simpler • Perhaps made by Archimedes of Syracuse, Sicily • Known for great inventions • Between 29 and 70 gears wheels for more complicated calculations • (some gears missing) • Tower of the Winds in Athens • Sebius water clock inside • Egyptian inventor • Antikythera mechanism • A computer for horoscopes • Perhaps every town had a tower, a water clock, and a mechanism

18. The Greeks: First Millennium BCE

19. Greek Reason • Thales ~700BCE • Lodestone • Amber • Anaximander ~ 650 BCE • Attempted to describe the mechanics of celestial bodies • Socrates ~400 BCE • “The Cave” • We see reality as shadows on the cave wall • Plato: student of Socrates

20. Plato’s Republic: The Myth of Er • Er was a character in Republic • Whorl (spindle) Of Necessity • Celestial Spheres

21. Eudoxus of Cnidus ( 408-355 BCE) • Colleague of Plato • Originator of scientific astronomy • No works survive • Envisioned a system of 20 concentric spheres • Spheres because of their symmetry and unity • Earth centermost • Rotational axis fixed to next largest sphere Introduction of epicycles

22. First Principles

23. Timeaus: • 2 Circles Split • Circle of the Same • Celestial Equator • Circle of the Different • Ecliptic

24. Quadrivium: Greek Learning • Arithmetic: number • Geometry: number in space • Music: number in time • Astronomy: number in motion

25. Five Perfect Solids (Things to come)

27. Aristotle 384-322 BCE • Student at Plato’s Academy / Teacher for Alexander • Each terrestrial element (earth, water, air, fire) has a natural place or state; some amount of each element is present in every body • Gravity/Levity • If a body (animate or inanimate) is removed from the natural place or state of its predominant element (violent change), it will naturally strive to return where it belongs (natural change) • physis

28. Metaphysics • For Aristotle, his “First Philosophy”, coming after physis • For us, the study and doctrine of internal, active principles in things • Intrinsic properties or qualities • Examples • The intrinsic nature of rock is ‘heavy’, and it seeks the center of the Earth • NOT that Earth’s mass pulls it down • The intrinsic nature of fire is ‘not heavy’ and it reaches upward • NOT that convection currents steer the flames • Not until the 17th century will these ideas be challenged

29. Influence felt for almost 2000 years • Adopts (and adapts) Eudoxus’ spherical model • Geocentrism • Earth at the center because it’s heavy • And spherical (!) contrary to myths of a flat world • Not a mathematician • Simplifies model • Calls the outermost sphere the “Prime Mover” • Remember, each axis fixed to the next outer sphere • Adopted later by the Roman Church as God • Earth where man lives • The Underworld of fire and brimstone

30. The Hellenistic Era • The time right after the death of Alexander • 323 - 31 BCE, when Rome emerges • Commerce flourishes • Greek culture had been spread over a wide area • Museum at Alexandria: 400,000 scrolls • Center of learning for hundreds of years • Burned by zealots in 415 AD • Librarian and Philosopher Hypatia killed for heresy

31. The Hellenistic World

32. Aristarchos 310-230 BCE • Had a different cosmological view than Aristotle: Heliocentrism • Found the ratio of the Earth to Moon diameter

33. Erastosthenes 276 - 194 BCE • Determined the size of the Earth, the distance to the Moon, and the size of the Moon, all very accurately.

34. Apollonius of Perga 190 – 120 BCE • Mathematician • Conic sections • Math 80 • Introduced eccentric orbits

35. Hipparchus of Rhodes 190-120 BCE • Precession of the equinoxes • Devised the Magnitude Scale for his catalog • Clumsy but still in use (modified heavily) today • Then, brightest star (Sirius) = 1, dimmest = 6 • Now Vega is labeled zero, brighter objects are negative, very dim objects are 20-30 • Took centuries of Babylonian observations and tried to reconcile the data with a combination of epicycles and eccentric orbits • In sexigesimal! • He made it work for the moon…

37. Retrograde Motion • Apparent backwards motion of planētēs in the sky • Wanderers; not the Sun or Moon • Difficult to reconcile with Aristotle - geocentrism

39. *Ptolemy (Claudius) 90-168AD • Mathematician, Astronomer, and Astrologer • Star catalog of 1000 stars in 48 constellations • Maybe Hipparchus’ catalog • Tetrabiblios: Astrology text • Scornful of previous 3 centuries of astronomy/astrology *Ptolemy I was one of Alexander’s generals. He was given governorship of Egypt by Alexander and the Ptolemys ruled the country for centuries. Note the cross-staff

40. The Mathematike Syntaxis • “The Mathematical Compilation” • …that the heavens are spherical and move spherically; • …that the earth, in figure, is sensibly spherical also when taken as a whole • …[that the earth] in position, lies right in the middle of the heavens, like a geometrical center; • …[that the earth] in magnitude and distance, has the ratio of a point with respect to the sphere of the fixed stars, having itself no local motion at all. • Incorporates Hipparchus’ equinox precession for accurate for predicting planetary positions for many centuries

41. Epicycles, Eccentrics, and now the Equant Equant point deferent

43. Planetary Hypothesis • Ptolemy reasoned that longer period planets are closer to the stars, furthest from Earth • Saturn, Jupiter, Mars far, Moon closest • Sun, Mercury, Venus a problem • Since Mercury and Venus are solar companions, he put the Sun nearer than Mars, then Venus and Mercury with little evidence • Distances: • Moon: 64 Rearth • ~256,000 miles;  • Stars: 19,865 Rearth • ~ 75 million miles 