Welcome to Astronomy 320

1. Welcome to Astronomy 320 Instructor : Clay Bratton Office: TBD Office Hours: TBD E-mail: cgbii@mac.com This is the best way to contact me.

2. Why should we be interested in Astronomy? • Personal curiosity about the world. • Predict the seasons. • Appreciate some of the “gee-whiz” technology we live with. • Understand our history better. Picture courtesy of Clive Ruggles

3. Ancient Peoples and the Stars • El Karnak • Example of Egyptian construction. • Oriented toward the sunrise of the winter solstice. • Why? Photo courtesy of Lyndsay Kyker

4. Chichen Itza • Astronomically oriented sites found all around the world • Cosmology of the Mayan’s was a living religious philosophy Picture courtesy of Clive Ruggles

5. Fajada Butte • Summer solstice. • Not all astronomical constructions were large. • These petroglyphs created by the Chacoans mark the motion of the Sun over the whole year. • They also mark the position of the Moon over an 18.6 year cycle. Courtesy of Bryan C. Bates

6. Big Medicine Wheel - Wyoming • Even nomadic or semi-nomadic peoples used astronomical sites. • Aligned with sun and several stars for rise on the summer solstice. Photo courtesy of Lyndsay Kyker

7. Stonehenge • Built in stages over several hundred years. • Possibly built to predict summer and winter solstices, eclipses and possibly more. Picture courtesy of Clive Ruggles

8. ARISTOTLE384 BC - 322 BC

9. Aristotle • Aristotle, more than any other thinker, determined the orientation and the content of Western intellectual history. He was the author of a philosophical and scientific system that through the centuries became the support and vehicle for both medieval Christian and Islamic scholastic thought: until the end of the 17th century, Western culture was Aristotelian. And, even after the intellectual revolutions of centuries to follow, Aristotelian concepts and ideas remained embedded in Western thinking. -The Catholic Encyclopedia.

10. Born on the Chalcidic pennisula of northern Greece. Student in Plato’s Academy in Athens. Established his own school the Lyceum. Endorsed and developed the idea of an axiomatic system for each science. On the Heavens Physics Aristotle

11. Aristotle • Aristotle put forward his notion of an ordered universe or cosmos. • Everything had its natural place, a privileged location for bodies with a particular makeup, and that the laws of nature were not the same in the heavenly and the earthly regions. • Earth was the center of the Cosmos. • Heavenly bodies were part of spherical shells of aether. • The cosmos encompassed all existence. • Aristarchus of Samos

12. PTOLEMY87 -150 AD

14. Ptolemy • Aristotle’s cosmology didn’t work! The heavenly bodies didn’t all seem to move in perfect circles. • Developed a new and improved model for motion of the heavens based upon eccentric, epicycle, and equant. • This was considered a minor refinement to Aristotle’s cosmology.

15. Sun, Moon, and stars all have simple movements in the sky • Planets: • Move with respect to fixed stars • Change in brightness • Change speed • Undergo retrograde motion

16. Epicycle

17. Eccentric

18. Equant

20. COPERNICUS1473-1543

21. Problems • Tables to determine timing of astronomical events not sufficiently accurate. • Sailing ships (Spanish & Portuguese) were sailing out of sight of land for weeks at a time and needed better astronomy to navigate. • Julian calendar was no longer accurate.

22. Copernicus • Placed the SUN at the center of the Universe. • Tried to downplay this as only a mathematical hypothesis. • De Revolutionibus Orbium Coelestium - published the year of his death. • Most sophisticated treatis since the Almagest • Placed on list of Forbidden Books!

25. Copernicus • Heliocentric view not accepted rapidly. • Required complete overturning of Aristotelian Physics! • Small parallax implied great distances.

27. Sun is at center of solar system. Only Moon orbits around Earth; planets orbit around Sun. This figure shows retrograde motion of Mars.

28. 2.4 The Birth of Modern Astronomy Phases of Venus cannot be explained by geocentric model

29. Announcements • First quiz will be given next Wednesday January 30th You should be reading Chapters 2 and 1. Chapter 2 will be covered on the first quiz.

30. TYCHO BRAHE1546-1601

31. Tycho Brahe • Born to Danish nobility. (Therefore, rich!) • Observatory - Uraniburg • Tycho designed and built new instruments, calibrated them, and instituted nightly observations. • Hired J. Kepler as an assistant to calculate planetary orbits.

33. Brahe • Developed a hybrid system where Moon and Sun went around the Earth but the planets revolved around the Sun. • First to correct for atmospheric refraction. • Showed the Heavens were not immutable. • New star 1572, comet 1577

36. KEPLER 1571-1630

38. Kepler’s First Law • All planets move about the sun in an elliptical orbit with the sun at one foci

39. 2.5 The Laws of Planetary Motion Planetary orbits are ellipses, Sun at one focus

40. More on Ellipses • All planets move in elliptical orbits. • The Eccentricity of and ellipse = (distance between foci)/(major axis of the ellipse) • The eccentricity for the orbits of all the planets is small (i.e. less than 0.1) except for Mercury and Pluto.

41. Kepler’s Second Law • The straight line joining the Sun and a planet sweeps out equal areas in equal intervals of time.

42. Kepler’s Third Law • The squares of the planets' orbital periods are proportional to the cubes of the semimajor axes of their orbits.

43. Kepler’s Third Law T2 = (4/GM)a3 Rearrange this a little and we get… T2 / a3 = 4/GM But 4 is a constant, as is G (Universal gravitational constant), and M (Mass of Sun).

45. GALILEO GALILIE Linceo 1564 - 1642

46. Galileo • Contemporary of Brahe and Kepler • Wanted to be a Camaldolese monk but his father insisted he train to be a physician at the University of Pisa. • Discovered he had a talent and interest in Mathematics. (G.E. Course?) • La Balancitta - 1586 • Lectured on dimensions of HELL - 1588

47. Galileo • Appointed to chair of mathematics at Pisa • Wrote (but did not publish) De Motu • Moved to University of Padua - 1592 • Argues against Aristotle! (Kepler’s star - 1604)

48. Galileo • Wrote in a personal letter to Kepler he believed in the Copernican cosmology. • By 1604 he had discovered correct descriptions of the motion of falling bodies and projectiles. • 1609 - received reports of a spyglass constructed by a Dutchman. Immediately built his own.

50. First sketch of a telescope