The great tragedy of science the slaying of a beautiful hypothesis by an ugly fact. -Thomas Huxley. Monday, October 3, 2011

Transcription

1 The great tragedy of science the slaying of a beautiful hypothesis by an ugly fact. -Thomas Huxley 1

2 Chapter 4 The Origin of Modern Astronomy

3 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

4 Ancient Greek Astronomers Earth s shadow is round as seen during an 4 eclipse

5 Eratosthenes (~ 200 B.C.): Calculation of the Earth s radius 7 7 5

6 Eratosthenes (~ 200 B.C.): Calculation of the Earth s radius 7 7 5

7 Scale of the Solar System Size of the Earth + Lunar Eclipse Observations Size of Moon!!! 6

8 Scale of the Solar System Size of the Moon + Angular Size in Sky Distance to Moon!!! 7

9 Scale of the Solar System Distance to the Moon + Sun/Moon Angle Distance to Sun!!! 8

10 Scale of the Solar System Distance to the Sun + Angular Size in Sky Distance to Sun!!! 9

11 Structure of the Solar System 10

12 Geocentric Models 11

13 Geocentric Models Eudoxus ( B.C.): Model of 27 nested spheres 11

14 Geocentric Models Eudoxus ( B.C.): Model of 27 nested spheres 11

15 Geocentric Models Eudoxus ( B.C.): Model of 27 nested spheres Aristotle ( B.C.), major authority of philosophy until the late middle ages: Universe can be divided in 2 parts: 11

16 Geocentric Models Eudoxus ( B.C.): Model of 27 nested spheres Aristotle ( B.C.), major authority of philosophy until the late middle ages: Universe can be divided in 2 parts: 1. Imperfect, changeable Earth, 11

17 Geocentric Models Eudoxus ( B.C.): Model of 27 nested spheres Aristotle ( B.C.), major authority of philosophy until the late middle ages: Universe can be divided in 2 parts: 1. Imperfect, changeable Earth, 2. Perfect Heavens (described by spheres) 11

18 The Wanderers Planet: from Greek πλανήτης αστήρ planētēs astēr "wandering star" 12

19 The Wanderers Planet: from Greek πλανήτης αστήρ planētēs astēr "wandering star" Motion of the planets across the sky is markedly different than the motion of the stars. Retrograde (westward) motion of a planet occurs when the Earth passes the planet. 12

20 Refinements to Geocentric Models Ptolemy s epicycles (150 AD) Publication: Syntaxis (the greatest) Model survived until Copernican Revolution of 1500 s. 13

21 Middle Ages Islamic Period: AD High regard for the science Religious motives for accurate timekeeping and astronomical observations Translated Greek texts into arabic Ptolemy s Syntaxis (arabic: Almagest) Contained a catalogue of > 1,000 stars All were given arabic names Measured 23.5 tilt of Earth s rotational axis with great precision. 14

22 Stellar Parallax

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

24 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.

25 Stellar Parallax Parallax angle of the nearest star is less than 1/3600 of one degree. Ancient astronomers tried to measure parallax via careful nakedeye observations but failed. Finally detected in 1830 by F. Bessel using telescope. 16

26 We want to put a telescope on one of the planets to measure the parallaxes of stars in our galaxy. Would it be better to put the telescope on Mercury or Mars? Why? 17