Monday, October 3, 2011

Transcription

1 We do not ask for what useful purpose the birds do sing, for song is their pleasure since they were created for singing. Similarly, we ought not ask why the human mind troubles to fathom the secrets of the heavens the diversity of the phenomena of Nature is so great, and the treasures hidden in the heavens so rich, precisely in order that the human mind shall never be lacking in fresh nourishment. ~ Johannes Kepler, Mysterium Cosmographicum, published in

2 Homework: due Monday, October 3 Chapter 4: Review Questions: 4, 7, 9, 10 Problems: 3, 5 (do 2 and 4 for practice; check answers in back of text) For practice with Kepler s Laws: kepler.html Next quiz: Wednesday, October 5 content: Chp 2,3,4 Review past quizes! 2

3 Chapter 4 The Origin of Modern Astronomy

4 Outline I. The Roots of Astronomy A. Archaeoastronomy B. The Astronomy of Greece C. Aristotle and the Nature of Earth D. The Ptolemaic Universe II. The Copernican Revolution A. Copernicus the Revolutionary B. De Revolutionibus C. Galileo the Defender D. The Trial of Galileo III. The Puzzle of Planetary Motion A. Tycho the Observer B. Tycho Brahe's Legacy C. Kepler the Analyst D. Kepler's Three Laws of Planetary Motion E. The Rudolphine Tables IV. Modern Astronomy

5 Stellar Parallax

6 Stellar Parallax We can judge distances to objects because we observe the world through two vantage points -- two eyes.

7 Stellar Parallax We can judge distances to objects because we observe the world through two vantage points -- two eyes. Greeks assumed the Earth was not moving because they did not observe parallaxes in the sky.

8 N. Copernicus ( ): G. Galilei ( ): As the giver of life, he believed Sun should be placed at the center of the Universe. Believed that the Ptolemaic model had become too clumsy and complicated. Conducted experiments on the nature of motion. Observed celestial objects with telescope, proving that the Sun is at the center of the solar system. 6

9 Galileo Galilei ( ) Invented the modern view of science: Transition from a faith-based science to an observation-based science

10 Galileo Galilei ( ) Invented the modern view of science: Transition from a faith-based science to an observation-based science Greatly improved on the newly invented telescope technology, (But Galileo did NOT invent the telescope!)

11 Galileo Galilei ( ) Invented the modern view of science: Transition from a faith-based science to an observation-based science Greatly improved on the newly invented telescope technology, (But Galileo did NOT invent the telescope!) Was the first to meticulously report telescope observations of the sky to support the Copernican Model of the Universe

12 Major Discoveries of Galileo Moons of Jupiter (4 Galilean moons)

13 Major Discoveries of Galileo Moons of Jupiter (4 Galilean moons)

14 Major Discoveries of Galileo Moons of Jupiter (4 Galilean moons)

15 Major Discoveries of Galileo Moons of Jupiter (4 Galilean moons) Rings of Saturn

16 Major Discoveries of Galileo Moons of Jupiter (4 Galilean moons) Rings of Saturn (What he really saw)

17 Major Discoveries of Galileo Moons of Jupiter (4 Galilean moons) Rings of Saturn (What he really saw)

18 Major Discoveries of Galileo 9

19 Major Discoveries of Galileo (2) Surface structures on the moon; first estimates of the height of mountains on the moon

20 Major Discoveries of Galileo (2) Surface structures on the moon; first estimates of the height of mountains on the moon

21 Major Discoveries of Galileo (2) Surface structures on the moon; first estimates of the height of mountains on the moon

22 Major Discoveries of Galileo (3) Sun spots (proving that the sun is not perfect!)

23 Major Discoveries of Galileo (4) Phases of Venus (including full Venus ), proving that Venus orbits the sun, not the Earth!

24 Major Discoveries of Galileo (4) Phases of Venus (including full Venus ), proving that Venus orbits the sun, not the Earth!

25 Major Discoveries of Galileo (4) Phases of Venus (including full Venus ), proving that Venus orbits the sun, not the Earth!

26 Tycho Brahe ( ) and Johannes Kepler ( ) Brahe was a meticulous observer. His greatest contribution to astronomy was a catalog of planetary positions. Like his predecessors, he tried to measure stellar parallax. Kepler had the ingenuity necessary to interpret Brahe s observations. Came up with three empirical laws describing planetary motion. 13

27 July 19,

28 July 19,

29 July 19,

30 July 19,

31 July 19,

32 July 19,

33 July 19,

34

35 1609

36 Johannes Kepler ( )

37 Johannes Kepler ( ) Used the precise observational tables of Tycho Brahe to study planetary motion mathematically.

38 Johannes Kepler ( ) Used the precise observational tables of Tycho Brahe to study planetary motion mathematically. Found a consistent description by abandoning both

39 Johannes Kepler ( ) Used the precise observational tables of Tycho Brahe to study planetary motion mathematically. Found a consistent description by abandoning both 1. Circular motion and

40 Johannes Kepler ( ) Used the precise observational tables of Tycho Brahe to study planetary motion mathematically. Found a consistent description by abandoning both 1. Circular motion and 2. Uniform motion

41 Johannes Kepler ( ) Used the precise observational tables of Tycho Brahe to study planetary motion mathematically. Found a consistent description by abandoning both 1. Circular motion and 2. Uniform motion Planets move around the sun on elliptical paths, with non-uniform velocities.

42 Kepler s Laws of Planetary Motion

43 Kepler s Laws of Planetary Motion 1. The orbits of the planets are ellipses with the sun at one focus.

44 Kepler s Laws of Planetary Motion 1. The orbits of the planets are ellipses with the sun at one focus. c

45 Kepler s Laws of Planetary Motion 1. The orbits of the planets are ellipses with the sun at one focus. c a=semi-major axis c=distance between focus and center of ellipse. Eccentricity e = c/a

46 Eccentricities of Ellipses 1) 2) 3) e = 0.02 e = 0.1 e = 0.2 4) 5) e = 0.4 e = 0.6

47 Eccentricities of Planetary Orbits Orbits of planets are virtually indistinguishable from circles:

48 Eccentricities of Planetary Orbits Orbits of planets are virtually indistinguishable from circles: Earth: e =

49 Eccentricities of Planetary Orbits Orbits of planets are virtually indistinguishable from circles: Earth: e = Most extreme example: Pluto: e = 0.248

50 Planetary Orbits (2)

51 Planetary Orbits (2) 2. A line from a planet to the sun sweeps over equal areas in equal intervals of time.

52 Planetary Orbits (2) 2. A line from a planet to the sun sweeps over equal areas in equal intervals of time.

53 Planetary Orbits (3) 3. A planet s orbital period (P) squared is proportional to its average distance from the sun (a) cubed:

54 Planetary Orbits (3) 3. A planet s orbital period (P) squared is proportional to its average distance from the sun (a) cubed: P y 2 = a AU 3

55 Planetary Orbits (3) 3. A planet s orbital period (P) squared is proportional to its average distance from the sun (a) cubed: P y 2 = a AU 3 (P y = period in years; a AU = distance in AU)

56 Planetary Orbits (3) 3. A planet s orbital period (P) squared is proportional to its average distance from the sun (a) cubed: P y 2 = a AU 3 (P y = period in years; a AU = distance in AU)

57 Planetary Orbits (3) The semi-major axis of Mars is 1.5 AU. How long does it take Mars to orbit the Sun once? 23

58 Planetary Orbits (3) The semi-major axis of Mars is 1.5 AU. How long does it take Mars to orbit the Sun once? 23

59 Planetary Orbits (3) Jupiter orbits the Sun about once every 12 years. Scientists discover a planet orbiting another star exactly like the Sun. This planet is two times closer to its parent star than Jupiter is from the Sun. How long does it take this planet to orbit its star? a) 5.2 years b) 18 years c) 1.9 years d) 4.2 years e) 95 years f) 7.6 years 24

60 Planetary Orbits (3) Kepler s third law (that the period squared is proportional to the semi-major axis cubed) does NOT apply to the motion of: a) a satellite around the Earth b) a comet around the Sun c) one star about another binary star d) one galaxy about another e) it applies to all of the above 25

61 Historical Overview