History & Development of Astronomy

1. History & Development of Astronomy • Retrograde motion • The Greek Models • Geocentrism, Epicycles, & the Church • Copernicus • Tycho Brahe • Kepler • Galileo

2. What did ancient civilizations achieve in astronomy? • Daily timekeeping • Tracking the seasons and calendar • Monitoring lunar cycles • Monitoring planets and stars • Predicting eclipses • And more…

3. Days of the week were named for Sun, Moon, and the 5 visible planets.

4. Ancient people of central Africa (6500 B.C.) could predict seasons from the orientation of the crescent moon.

5. Egyptian obelisk: Shadows tell time of day.

6. England: Stonehenge (completed around 1550 B.C.)

7. Mexico: model of the Templo Mayor

8. New Mexico: Anasazi kiva aligned north–south

9. SW United States: “Sun Dagger” marks summer solstice

10. Scotland: 4,000-year-old stone circle; Moon rises as shown here every 18.6 years.

11. Peru: lines and patterns, some aligned with stars

12. Macchu Pichu, Peru: structures aligned with solstices

13. South Pacific: Polynesians were very skilled in the art of celestial navigation.

14. France: Cave paintings from 18,000 B.C. may suggest knowledge of lunar phases (29 dots).

15. "On the Jisi day, the 7th day of the month, a big new star appeared in the company of the Ho star." "On the Xinwei day the new star dwindled." Bone or tortoiseshell inscription from the 14th century B.C. China: earliest known records of supernova explosions (1400 B.C.)

16. Two Different Early Models… • GEOCENTRIC • Earth is the center of everything • Earth doesn’t spin or move

17. The Geocentric Model as art…

18. Two Different Early Models… • HELIOCENTRIC • The Sun is the center of the solar system • Earth spins (rotates) to create day/night • Earth orbits (revolves)to create the year

19. Geocentric Models made “sense” • GEOCENTRIC: Earth doesn’t move • If we did, we’d feel it! • If we did, we’d lose the moon! • If we did, the stars around us would shift! • THEREFORE: • Sky (& Stars!) rotated around us • Sun & Moon & Planets actually move among key constellations of the Zodiac by design/choice

20. Two Different Early Models… • HELIOCENTRIC: Earth moves about the Sun • So do all of the planets • The Moon goes around us, too • Earth spins to create night and day • THEREFORE: • Sky (& Stars!) just SEEM to rotate around us • Sun & Moon & Planets moved among key constellations of the Zodiac because of OUR motion

21. KEY IDEA: Retrograde motion of the planets • We make the observation that planets – and only the planets – “dance” in front of the stars. How is this observation explained in each model?

22. The Motion of the Planets in the sky over time

23. The Motion of Mars In 2009-2010

24. Retrograde Motion Explanations • Ancient (and geocentric) • The planets move on their own around us • God(s) control their motions • Heaven’s realm – doesn’t concern us! • It just is…

25. Retrograde Motion Explanations • Modern (and heliocentric) • Earth and other planets orbit the sun at different rates • Earth “laps” slower-moving outer planets – and they appear to loop

27. Retrograde Motion Explanations • Modern (and heliocentric) • Earth and other planets orbit the sun at different rates • Inner planets speed between us & sun one way, then seem to reverse along far side

28. Venus’ Different Views • Venus September 2013 – evening sky

29. Venus’ Different Views • Venus September 2013 – evening sky

30. Venus’ Different Views • Venus January 2013 – morning sky

31. Why does modern science trace its roots to the Greeks? • How did the Greeks explain planetary motion? • How did Islamic scientists preserve and extend Greek science? Artist’s reconstruction of the Library of Alexandria

32. Our mathematical and scientific heritage originated with the civilizations of the Middle East.

33. Why does modern science trace its roots to the Greeks? • Greeks were the first people known to make models of nature. • They tried to explain patterns in nature without resorting to myth or the supernatural. Greek geocentric model (c. 400 B.C.)

34. Eratosthenes measures the Earth (c. 240 B.C.) • Measurements: • Syene to Alexandria • distance ≈ 5,000 stadia • angle = 7°

35. Eratosthenes measures the Earth (c. 240 B.C.) Calculate circumference of Earth: 7/360  (circum. Earth) = 5,000 stadia  circum. Earth = 5,000  360/7 stadia ≈ 250,000 stadia Compare to modern value (≈ 40,100 km): Greek stadium ≈ 1/6 km  250,000 stadia ≈ 42,000 km

36. How did some Greeks explain planetary motion? Underpinnings of the Greek geocentric model: • Earth at the center of the universe • Heavens must be “perfect”—objects move on perfect spheres or in perfect circles. Plato Aristotle

37. But this made it difficult to explain the apparent retrograde motion of planets… Review: Over a period of 10 weeks, Mars appears to stop, back up, then go forward again.

38. How did other Greeks explain planetary motion? Sun-centered models had been considered • Philolaus: Sun – the central “fire” at the center of the universe • Aristarchus: Earth must be smaller • Archimedes: Stars must be MUCH farther away! Aristarchus Archimedes

39. The most sophisticated geocentric model was that of Ptolemy (A.D. 100–170) — the Ptolemaic model: • Sufficiently accurate to remain in use for 1,500 years • Arabic translation of Ptolemy’s work named Almagest (“the greatest compilation”) Ptolemy

40. So how does the Ptolemaic model explain retrograde motion?Planets really do go backward in this model.

41. Ptolemaic Retrograde Motion

42. Ptolemaic Retrograde Motion

43. What happened after Ptolemy’s model? • Theologically • Earth at the center of everything “fits” western religious growth in Christianity • Scientifically • Earth rotating and revolving mysteriously through “unseen” forces is hard to prove • Science was unnecessary…

44. The Roman Era

45. The Roman Era … Science should be “practical”

46. The Fall of Rome

47. The Looting of the Library of Alexandria

48. The Dark Ages…..

49. The Dark Ages….. In Europe…

50. The Dark Ages….. In Europe… Not in the Middle East, China, The Yucatan, Polynesia….