Ancient Astronomy

1. Ancient Astronomy Astronomy – the most ancient of the sciences Astronomical records back to prehistoric times

2. Scientific Methods —Common Steps Recognize a question, a puzzle, or an unexplained fact. Make a hypothesis (educated guess) to resolve the puzzle. Predict consequences of the hypothesis. Perform experiments or make calculations to test the predictions. Formulate the simplest general rule that organizes the three main steps.

3. The Scientific Attitude The scientific attitude is one of inquiry. experimentation. willingness to admit error.

4. The Scientific Attitude Fact is a close agreement by competent observers who make a series of observations about the same phenomenon. A scientific hypothesis is an educated guess that is only presumed to be factual until supported by experiment.

5. Which of these is a scientific hypothesis? The Moon is made of green cheese. Atomic nuclei are the smallest particles in nature. A magnet will pick up a copper penny. Cosmic rays cannot penetrate the thickness of your textbook. The Scientific Attitude CHECK YOUR NEIGHBOR

6. Which of these is a scientific hypothesis? The Moon is made of green cheese. Atomic nuclei are the smallest particles in nature. A magnet will pick up a copper penny. Cosmic rays cannot penetrate the thickness of your textbook. The Scientific Attitude CHECK YOUR NEIGHBOR Explanation: All are scientific hypotheses! All have tests for proving wrongness, so they pass the test of being a scientific hypothesis.

7. Oldest star chart- 32,000 years ago (Orion?)

8. Stonehenge – 3100 – 2100 BC

10. Great Pyramid at Khufu (Cheops) – 2600 B.C. Aligned within 1/20 degree of true north Possible correlations with astronomical objects?

11. Chichen Itza – Mayan observatory

12. Medicine Wheel – Northern Wyoming

13. Chaco Canyon – supernova of 1054?

14. Chaco canyon – Anasazi sun dagger – A.D. 400-1300, marks summer solstice

15. Constellations Apparent groupings of stars – relatively fixed positions

16. Constellations – the 88 semi-rectangular regions that make up the sky

17. Star trails

19. Star trails around South Celestial Pole (Gemini Observatory, Chile)

20. Most of modern astronomy and cosmology comes from the Greeks

21. Celestial Sphere

22. The Geocentric View Aristotle’s View: The Most Perfect Form is the Circle The Crystalline Spheres

23. The Motion of the Earth Correct Method - Wrong Conclusion • Parallax: The apparent motion of an object due to the motion of the observer. • The Greeks could not detect any parallax for the stars (or planets). • Conclusion: • The Earth is not moving. OR • The Stars are too far away to measure parallax with crude instruments / eye. • The Greeks chose not moving.

24. Aristarchus310 - 230 BC Heliocentric model Determined relative distances between Sun and Moon

25. α The Distance to the Sun Aristarchus of Samos ~ 310 - 230 BCE • Aristarchus measured  to be 87 degrees • Sun Distance = 19 Moon Distance • (today: Sun is about 400 times further away than moon) First Quarter Moon Third Quarter Moon

26. Ptolemy (85 – 165 A.D) Lived in Egypt, probably Alexandria Summarized Greek astronomy in the Almagest Geocentric model of solar system

28. Epicycles and Equants Everything circles something else…

29. Very complicated – but it worked! (sort of) http://astro.unl.edu/naap/ssm/animations/ptolemaic.swf http://astro.unl.edu/animationsLinks.html#ca_renaissance

30. Major assumptions of the Ptolemaic model • All motion in the heavens is uniform circular motion. • The objects in the heavens are made from perfect material, and cannot change their intrinsic properties. • The Earth is at the center of the Universe.

31. After the Greeks: • Alexandria burns in 272 A.D., Roman empire collapses, and Europe enters Dark Ages • Roman Catholic Church combines Ptolemaic with Aristotelian thought into official church doctrine – Earth as immovable center of cosmos • Much of astronomy is carried forth by Persian and Islamic astronomers who preserved Greek thought and refined it – named many stars we know today

32. Breaking through the old model…

33. Major problems with the Ptolemaic System:It failed to…. Accurately predict eclipses (off by hours, days, etc…) * Predict position of planets accurate enough *Couldn’t explain meteors, comets, supernovae

34. Nicolas Copernicus (1473-1543) – proposed heliocentric hypothesis, mostly on philosophical grounds

35. Copernicus’ model: • Gave similar predictions to Ptolemaic model, also used epicycles, etc… • Proposed earth rotates on axis to cause night and day • Proposed earth and other planets travel around sun • Radical idea for time –this sounded crazy to most people!!!

36. De Revolutionibus Orbium Coelestium, 1543 (On the Revolutions of the Heavenly Spheres)

37. Copernicus’ explanation of retrograde motion

38. Galileo 1564 - 1642 • All bodies fall at same rate!! - Tower of Pisa

39. Galileo’s Telescope • Galileo’s telescopic observations led him to firmly reject the geocentric model.

40. The Milky Way was composed of millions of stars.He realized that wherever he looked, he saw more and more stars……

41. SaturnGalileo noticed….“Saturn has ears”

42. SunspotsA. The surface of the Sun was imperfect. B. apparent motion of the spots across the Sun's disk implied rotation.

43. Detailed moon drawings – the moon is not a smooth sphere!

44. The Galilean Satellites • They Orbit Jupiter! • So Why Cannot the Planets Orbit The Sun

45. The Phases of VenusGalileo noticed that when Venus wanes (becomes crescent), it becomes larger.

46. The Phases of Venus