Download Ancient Astronomy: From Geocentric to Heliocentric Model and more Study notes Astronomy in PDF only on Docsity! 1 Astro 120 Fall 2005: Lecture 8 page 1 Reading: Chapter 3, Sections 3.3 – 3.5 Chapter 5, Sections 5.1 – 5.3 A Brief Review of Last Time • planetary motions - eastward motion - retrograde loops - near ecliptic - Venus & Mercury near Sun • planetary alignments -conjunctions, oppositions, -synodic period - transits Astro 120 Fall 2005: Lecture 8 page 2 Today • Ancient Greek Astronomy - The geocentric model • Copernicus - The heliocentric model Reading: Chapter 3, Sections 3.3 – 3.5 Chapter 5, Sections 5.1 – 5.3 Astro 120 Fall 2005: Lecture 8 page 3 Spherical Earth Pythagoras of Samos (~500 BC) First person to suggest the Earth is a sphere. Astro 120 Fall 2005: Lecture 8 page 4 Spherical Earth •ships disappeared before they appeared as points 2 Astro 120 Fall 2005: Lecture 8 page 5 1540 textbook The shape of the Earth’s shadow during lunar eclipses Astro 120 Fall 2005: Lecture 8 page 6 Aristotle argued strongly for a spherical Earth. One of his arguments considered the visibility of stars at different places. N Aristotle (c. 350 BC) Astro 120 Fall 2005: Lecture 8 page 7 Aristotle (c. 350 BC) He developed a very influential philosophy/ model of the universe. -The four basic elements (Earth, water, air, fire) tend towards their “natural places”, -The Earth is a small spherical body at the center or “bottom” of a series of concentric spheres, -The lower levels are most subject to change, the highest ones are perfect and unchanging. Astro 120 Fall 2005: Lecture 8 page 8 Sun, Moon, planets, and stars located on concentric spheres with Earth at center 5 Astro 120 Fall 2005: Lecture 8 page 17 Hipparchus (c. 100 BC) • Produced earliest catalog of brightest stars • systematic observer • Discovered precession of the equinoxes • Developed quantitative geometrical models of the moon and Sun’s motion Astro 120 Fall 2005: Lecture 8 page 18 Ptolemy (c. 150 AD) The last great astronomer of antiquity. The Almagest Geometrical models & related tables by which the movements of the planets could be calculated. Astro 120 Fall 2005: Lecture 8 page 19 Ptolemy (c. 150 AD) • Continued to modify circular motion Center of epicycle moves at a variable speed so that it appears to be moving uniformly as seen from the equant. This bothered astronomers for the next 1500 years! Planet on “epicycle” Earth Equant slow fast Astro 120 Fall 2005: Lecture 8 page 20 Earth at center (sort of…) Epicycle 6 Astro 120 Fall 2005: Lecture 8 page 21 Epicycles for Venus & Mercury constrained along Earth-Sun line No good reason for this order Astro 120 Fall 2005: Lecture 8 page 22 Middle Ages “astronomers… would struggle to master the intricacies of the Almagest, against a background of philosophical disquiet at the devices Ptolemy had found it necessary to employ”. Eccentric circles, Epicycles & Equant points Astro 120 c. 1100 AD Astro 120 Fall 2005: Lecture 8 page 23 Nicolaus Copernicus (b. 1473 d. 1543) • Proposed a Sun-centered model of the Solar System • He did not have any new observations that refuted the Ptolemaic model Astro 120 Fall 2005: Lecture 8 page 24 Nicolaus Copernicus • studied at University of Cracow (1491) • studied canon law and medicine in Italy - developed interest in astronomy and Greek • church administrator in Poland (1503- 1543) - ideas develop, circulated amongst friends 1543 – De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Spheres) Contained both a philosophical discussion and lots of detailed calculations 7 Astro 120 Fall 2005: Lecture 8 page 25 De Revolutionibus Orbium Coelestium (1543) Astro 120 Fall 2005: Lecture 8 page 26 De Revolutionibus Orbium Coelestium (1543) Orbital Period Distance Mercury Venus Earth Mars Jupiter Saturn Mercury 0.38/0.387 Venus 0.72/0.723 Earth 1/1 Mars 1.52/1.52 Jupiter 5.22/5.20 Saturn 9.18/9.54 Astro 120 Fall 2005: Lecture 8 page 27 “But you are rather waiting to hear from me how it occurred to me to venture to conceive any motion of the earth, against the traditional opinion of astronomers and almost against common sense.” Astro 120 Fall 2005: Lecture 8 page 28 - A rotating Earth seemed more reasonable than a starry sphere that rotated every 24 hours - He considered his model more elegant and unified: - retrograde motion - order of planets - orbital period of planets - a return to uniform circular motion The answer…
