1. Ancient medicine wheel
Early history
Ancient medicine wheel

2. What Is A Cosmology? View of the universe and our place in it
Always has:
Layout of the universe
Often has:
Associated creation story
Fundamental human question: is there a meaning to our existence?
Method to explain celestial motion (movement of the planets and stars)

3. Earliest Cosmologies (3000+ BC)
Earth is flat
Universe centered on individual
Size of universe limited to local environment
Sun and moon important?
Cave paintings feature disk with rays (sun?) and “spots and crescents” (phases of the moon?)
Hunter-gatherer: value in understanding motions of stars and planets (useful in predicting winter)?
No evidence of concept of “celestial sphere”
Creation myths virtually unknown

4. Stonehenge (2800 BC – 1100 BC)
Horizon astronomy (position of sun during solstices and equinoxes)
Star/planet position not important
Calendar
Associated cosmology?
Probably not: utilitarian tool

5. Caracol (Maya culture, ~A.D. 1000)
Oriented to face sunsey at the summer solstice.
Furthest point North on ecliptic

6. Paint Rock, Texas
Petroglyphs

7. Archeoastronomy
Knowledge of motions of sun and moon allows prediction of seasons.
Important for agriculture
Agriculture important for rise of civilization.

8. Archeoastronomy
Astronomical knowledge important to religious/elite classes.
Perceived power: ability to “control” the objects in the heavens.

9. Mesopotamian Earliest - 6000years ago
Calendar derived – Had 12 & 13 months
First zodiacal signs
Originated idea of 360 ̊ circle, divided into 60 minutes and seconds
The degree symbol is based on the sun

10. Babylonian Astronomy (500BC)
Advanced calendar
Ability to predict planetary motion
Subtle shift in cosmology:
World is flat, but much larger than local environment.
Sky is a “vault” containing the stars.
Sun and moon moves through the sky. Fundamentally different from planets/stars.

11. Babylonian Astronomy
Precise understanding of solar/lunar motion necessary for lunar calendar.
Great interest in understanding planetary motion – associated with predictions of fate first with large things- war, floods then individuals (astrology).

12. Babylon and Mathematical Astronomy
Early records are observationally based.
Records found from 1500 BC and before.
Highly accurate mathematics developed to predict future motion.
Math ultimately supplants observation.
No 3d model – highly abstract.
No system for the solar system as a whole, just objects.

13. Egyptian Astronomy
Little interest in mathematical astronomy, or the sky:
Only five named constellations (records from 1100 BC).
Partial reason: Ancient Egypt lacks the mathematical sophistication of Babylon.
No real records of how they did it.

14. Egyptian Astronomy Limited to the practical:
36 decans (“star groups”) used to tell time at night.
First appearance of Sirius heralds annual flood of Nile.
Orientation of major monuments based on sun worship and significant constellations (like Orion – Osiris in Egyptian myth)

15. Greek Astronomy
“Classical Revolution” begins c.700 BC and runs until 200AD.
Assume Egyptian influence but not well documented
Astronomy used for timekeeping. Techniques imported from Babylon and Egypt.
Example from Hesiod – Pleiades star cluster used to track time for use in agriculture (Pleiades = harvest time for grapes).

16. Successful prediction of solar eclipse
Thales B.C.
Successful prediction of solar eclipse
Anaximander – B.C.
Wheel model of solar system , earth is central cylinder (round)
Anaximenes B.C.
Vault with jewels – Gave beginnings to celestial sphere (shows curvature)

17. Greek Astronomy Pythagoras (c.500 BC):
Earth is a sphere, as are all celestial bodies (perfection)
Morning star and evening star (associated with Venus) are the same object
Celestial harmony. Listen to the beautiful music!!!!

18. Greek Astronomy Plato (c. 360 B.C.)
Plato (c. 360 B.C.)
Established a philosophy based on the teachings of Pythagoras that favored mental reasoning power over observational science
Taught that what is seen in the natural world is an imperfect representation of ideal creation
Teachings dominated much of Western philosophy and science for about 2,000 years

19. Greek Astronomy
Models based on the philosophy of Plato were generally wrong because they were based on wrong “first principles”, believed to be “obvious” and not questioned:
Geocentric Universe: Earth at the Center of the Universe and stationary. “we don’t sense motion”
“Perfect Heavens”: Motions of all celestial bodies described by motions involving objects of “perfect” shape, i.e., spheres or circles.

20. Greek Astronomy Eudoxus (c.360 BC)
Complex motions of planets through the sky can be explained through simple circular motion.
Planets located on giant “crystal” spheres with Earth at the center. (notice Sphere usage)
Model of 27 nested spheres

21. Greek Astronomy
Greeks are first to devise a “model” that tries to explain (not just document and predict) these motions!
Circles / Spheres important in Greek philosophy (“the most perfect shapes”) – so model is based on spheres.

22. Aristotle (384 – 322 BC)
Eudoxus’ ideas refined by Aristotle (c.350 BC):
Earth is spherical at center of universe. Supported by shadow on moon.
“Edge” of universe is a literal celestial sphere holding the fixed stars. Sphere rotates around earth.
Spherical shape based on “gravity” all things fall straight down to center.

23. Aristotle’s Universe
Would dominate astronomical thought for the next 2,000 years!

24. Aristarchus (310 BC – 230 BC)
Measured relative distances/sizes of sun and moon:
Moon is about 1/3rd the size of Earth.
Sun 20 times farther than moon and 7 times larger than Earth.
Since sun is larger, he reasons it must be at the center of universe.
First known heliocentric cosmology.

25. Some Incredible Insights
Aristarchus Develops Heliocentric Idea:
Moon shines because it reflects light from the sun.
Stars show no parallax:
Must be extremely far away
If viewed close up, must be as large and bright as the sun
Must be “distant suns”
Universe must therefore be MUCH bigger than indicated by Aristotle’s geocentric model.
Knowledge was limited by mathematical discoveries
Never did the math, just stated it “could” be done!
Hipparcos later did the math.

26. Aristotle Hijacks Science
Aristarchus’ hypothesis fails in the face of Aristotle’s philosophy. Common sense?
Why no perception of motion:
Earth rotates? Why don’t dropped objects fly off to the west?
Earth circles the sun? Why don’t we fly off its surface?
Ironically: Why no parallax?
Geocentric model wins the day!

27. Calculation of the Earth’s radius
Eratosthenes , Director of library of Alexandria(~ 200 B.C.)
Angular distance between Syene and Alexandria: ~ 7°
Linear distance between Syene and Alexandria: ~ 5,000 stadia
 Earth Radius ~ 40,000 stadia (probably ~ 14 % too large) – better than any previous radius estimate.
The noon angle represents difference in latitude

28. Hipparchus (c. 180 B.C.) Lived on a remote island.
Lived on a remote island.
Used naked-eye sighting instruments to aid observations
Introduced the use of celestial coordinates, made star maps (850 stars)
Invented the magnitude scale

29. Hipparchus
Estimated and compared stellar brightness to earlier data collected
Used trigonometry in astronomy
Discovered the precession of the Earth's axis. 1 cycle takes 28000yrs. Creates a new “north star”
Maintained the idea of the Earth-centered (geocentric) universe, because he could not detect any hint of stellar parallax.

30. Parallax Hipparchus could not measure stellar parallax.
Hipparchus could not measure stellar parallax.
He concluded the earth must not be moving.
The reality is, distances to stars are too great to measure parallax.

31. Ptolemy (c A.D.)
Summarized all previous Greek astronomy in his book the Almagest.
Further refined the deferent/epicycle concept using the equant.
The point of uniform motion of the planet is off-center.

32. Introduced to explain retrograde (westward) motion of planets
Epicycles
Introduced to explain retrograde (westward) motion of planets

33. Later refinements (2nd century B.C.)
Hipparchus: Placing the Earth away from the centers of the “perfect spheres”
Ptolemy: Further refinements, including epicycles

34. Ptolemy’s Geocentric Model Of The Cosmos
His model was the most accurate predictor of planetary positions in the ancient world and was used as the model of the Cosmos up to the time of the Renaissance.