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Early Astronomies Astronomy 1-1 Lecture 03-1 Ancient Astronomies Astronomies were often necessary for determining the agricultural seasons The flooding of the Nile, closely related to the rising of the star Sirius Stonehenge related to astronomical occurrences such as the summer and winter solstices Mayans had a calendar based on Venus North American Indians had an astronomical device based on the summer and winter solstices Astronomy 1-1 Lecture 03-2 Cast of Characters Thales (c624-547BC) Rational inquiry. Pythagoras (c570.-500BC) Round Earth. Philolaus (c500-400BC) Celestial Harmonies. Anaxagoras (c500-428BC) Moon reflects sunlight; Eclipses. Plato (c428-347BC) Reason not observation. Eudoxus (c408-356BC) Mathematical cosmology. Aristarchus (c310-230BC) Size of sun, moon; Heliocentric theory. Eratosthenes (c273-?BC) Size of earth. Apollonius (c265-19OBC) Epicycle. Hipparchus (c200-100BC) Epicyclic theory of sun and planets. Ptolemy (c1OO-200AD) Elaborate epicycle theory; Almagest. Aristotle (c384-322BC) Physical Laws; Round earth. Astronomy 1-1 Lecture 03-3 Early Astronomies Babylonia ~3000BC Divided sky into 12 parts Numbering system based on 60 Circle divided into 360 degrees Chaldeans could accurately predict Solar, lunar, and planetary motions Lunar and solar eclipses Greece >1600BC Dome of Heavens. Earth floating dish. Astronomy 1-1 Lecture 03-4 Early Astronomies Thales Rational inquiry leads to understanding of universe beyond simple description. Pythagoras First to suggest Earth was round and that all heavenly bodies moved in circles. Philolaus Planetary distances correspond to lengths of vibrating strings producing harmonious sounds. Anaxagoras Moon shines by reflected light. Lead him to deduce eclipses caused by passage of one between the other two. Views considered sacrilegious. Exiled Astronomy 1-1 Lecture 03-5 Early Astronomies Plato What we see of material world is only imperfect representation of ideal creation. Can learn more about universe by reason than by observation, since observations can only give incomplete picture. Idealized assumptions. Eudoxus Put Plato's ideas on mathematical footing. Concentric spheres on which Sun, Moon, and planets moved. Astronomy 1-1 Lecture 03-6 Early Astronomies Aristotle Adopted physical laws and showed in terms of these why the universe functioned the way it did. Circular motion - the only natural motion. Earth not spinning since no great wind - so Earth is stationary. All circular motions centered about the Earth. Four basic elements: earth, air, fire, and water. Showed Earth and universe spherical. Three ways to show Earth spherical: 1) Only on sphere do things fall inwards, everywhere. 2) View of stars change as go north to south. 3) Shadow of Earth on Moon during eclipse is curved. Broke with Plato, in that he used data. Astronomy 1-1 Lecture 03-7 Early Astronomies Astronomy now moved from Greece to Alexandria in Egypt. Aristarchus Showed Sun was many times further than Moon and that Moon was smaller than Earth and that Sun was larger than Earth. Developed first heliocentric (Sun centered) theory. Up until this, all theories had been geocentric (Earth centered). Suggested that Earth rotated about its own axis. Astronomy 1-1 Lecture 03-8 Stellar Parallax Evidence for heliocentric theory could only come from stellar parallax What do we mean by parallax? Astronomy 1-1 Lecture 03-9 Parallax Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight Nearby objects have a larger parallax that more distant objects when observed from different positions Our brain uses parallax for gain depth perception Astronomy 1-1 Lecture 03-10 Stellar Parallax Stellar parallax is very small, much too small for instruments of the day So heliocentric theory was forgotten Astronomy 1-1 Lecture 03-11 Early Astronomies Eratosthenes Determined size of the Earth 39,690 km, an error of less than 1% Astronomy 1-1 Lecture 03-12 Early Astronomies Appollonius Improved models of concentric spheres with introduction of epicycle and deferent With adjustment of sizes of both, better match to data, especially the retrograde motion of some of the planets Astronomy 1-1 Lecture 03-13 Early Astronomies Hipparchus Refined work on epicycles Used trigonometry Refined instruments for measuring Stellar magnitude system Precession of star positions, by comparing his data with that from 160 years previous His refined data lead to an offset for the position of the Earth with respect to the center of the deferent Astronomy 1-1 Lecture 03-14 Early Astronomies No further significant work until 2nd century AD Ptolemy Almagest - a thirteen volume set of books Based partly on the works of Hipparchus Detailed studies of the sun, star charts, and astronomical instruments Detailed model of planetary motions, accurate to be used for the next thousand years Extended the idea of deferents and epicycles. Assumed Earth not at the center of the deferent Unclear as to whether he viewed this system as a mathematical tool or reality His model however was taken to be the literal truth for the next fourteen centuries. Astronomy 1-1 Lecture 03-15 Early Astronomies Alexandria remained intellectual center until its fall in 640AD. when library buildings were burned Europe fell into The DARK AGES. Other cultures, mainly Arabic, contributed to mainstream astronomy as they also needed accurate calendars Refined the works of Ptolemy and passed it back to Europe through Spain By thirteenth century serious discrepancies existed between observations and predictions New epicycles had to be added to obtain agreement again MUCH DISPLEASURE with complexity of model Astronomy 1-1 Lecture 03-16 Complexity Astronomy 1-1 Lecture 03-17