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PHYS 183 (51)
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Chapter 3

Chapter 3

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PHYS 183
Tracy Webb

3: The Science of Astronomy 3.2 Ancient Greek Science  civilization established in Egypt & Mesopotamia by 3000 B.C.  crossroads for travelers, merchants, armies from Europe, Asia & Africa (mixing of cultures  creativity & new ideas) o ancient Egyptians built Pyramids o Babylonians developed arithmetic  science came from ancient Greece  rose as power in Middle East 500 B.C.; developed 3 innovations: o developed tradition of understanding nature without relying on supernatural explanations and working communally to debate/challenge each other’s ideas o used math to give precision to ideas o power of reasoning from observations  synthesized all 3 innovations into ideal of creating scientific models  Greek models wanted to explain properties of matter & motions of stars, moon & planets  Greeks developed geocentric model of cosmos (earth-centered)  trace origin of Greek science to Thales  legendary prediction of solar eclipse’ first to address question what is the universe made of? o suggested universe consists of water & earth is a flat disk floating on infinite ocean o Anaximander suggested earth floats in empty space surrounded by stars & 2 rings which sun/moon travel  credited with inventing ideas of celestial sphere o Pythagoras  earth = sphere floating at center of celestial sphere o Aristotle  observations of earth’s curved shadow on moon during lunar eclipses = evidence of spherical earth o Plato  all heavenly objects move in perfect circles at constant speeds (must reside on huge spheres encircling earth)  Greeks found planets don’t move at constant speeds around Earth o Eudoxus  created model in which sun, moon & planets had own spheres within other spheres o Aristotle  all sphere responsible for celestial motion transparent & interconnected; egocentricity explain by gravity  Ptolemaic model o geocentric model o each planet moves around earth on small circle that turns upon larger circle  planet following this traces a loop, explaining apparent retrograde motion of planets o great accomplishment  adapt & synthesize earlier ideas into single system that agreed with astronomical observations at the time  Greeks had influence since they were good at politics, war & philosophy already o Alexander the Great expanded Greek Empire & encouraged pursuit of knowledge o founded Alexandria where a large library was built  preeminent research center for 700 years o books about the library were destroyed with the library o Egypt built a New Library of Alexandria (2003)  Muslims sought knowledge of mat & astronomy in hopes of better understanding wisdom of Allah o A.D. 800, House of Wisdom established  similar to Library of Alexandria o employed Jews, Christians & Muslims o most of the officials names of constellations & stars come from Arabic due to this work 3.3 The Copernican Revolution  what we now think of as science rose during European Renaissance  Copernican revolution: Copernicus changed the way we perceive our place in the universe  spurred development of virtually all modern science & technology th  Nicholas Copernicus  Torun, Poland, February 19 , 1473 - 1543 o began studying astronomy in late teens o discovered simple geometric relationships  could calculate each planet’s orbital period around sun & its relative distance from sun (convinced him of sun-centred idea) o hesitant to publish work, other scholars urged him to  De Revolutionibus Orbium Coelestium o scholars drawn to ideas but didn’t work well  had added many complexities to system by keeping idea heavenly motion occurs in perfect circles  Tycho Brahe  Denmark, 1546-1601 o interested in astronomy as young boy but parents discouraged interest  kept passion secret o 1563 observed alignment of Jupiter & Saturn  happened 2 days after date Copernicus said o used observations  famous for observed nova (new stars) in 1572  proved it was much further away from Moon o made similar observations of a comet in 1577 o compiled naked eye observations of 30 years o was convinced planets must orbit sun but inability to detect stellar parallax made him conclude earth stationary  Johannes Kepler  Germany, 1571 – 1630 o hired by Tycho to explain motions of planets o begged by Tycho on death bed to make sense of his work o worked hard to find a model for the orbit of Mars o discrepancies between his work and Tycho’s work made him abandon idea of circular
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