Notes_A%20BP

Notes_A%20BP - A1 History Development of celestial...

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Development of celestial mechanics naturally divides into two distinct parts I. Formal Astronomy II. Dynamical Astronomy Formal aspects of the universe Physical aspects of natural phenomena Phenomena apart from causes: Fundamental properties Æ Mention a few contributors to each A1 History
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1. Ancient Astronomers Noted natural divisions of time (day, month, year) Careful observations Time relationships known to considerable accuracy early in Chaldean (Babylonian) and Egyptian history Poor records Ideas pursued by Greeks I. Formal Astronomy (phenomena apart from its causes) Noted by primitive peoples First to think “ geometrically” A2
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2. Thales (640 -546 BC ) of Miletus in Asia Went to Egypt for instruction Taught sphericity of Earth, obliquity of ecliptic Determined length of year Predicted solar eclipse of 585 BC 3. Pythagoras (~ 569-475 BC ) Samos (off coast of Turkey) Traveled in Egypt and Chaldea Primarily a philosopher – no mathematical writings Founded School of Astronomy and Philosophy in Sicily Taught: Earth rotates; comets/planets in circular orbits Theano – wife of Pythagoras After his death, she took over the Pythagorean School with her two daughters She wrote on mathematics, physics, and medicine Her most important work: principle of the “Golden Mean” 4. Meton (~ 465-385 BC ) Greek mathematician, astronomer, geometer, and engineer; lived in Athens Accurate astronomical observations Noted in 432 BC: the 19-year Metonic cycle Phases of the Moon recur same days of year, same time of day Period of 19 tropical years is almost exactly equal to 235 synodic months, and rounded to full days counts 6940 days. Difference between two periods (of 19 tropical years and 235 synodic months) is only 2 hours Cycle's most significant contemporary use is to help in flight planning (trajectory calculations and launch window analysis) A3
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5. Aristotle (384 BC - 322 BC) Universe spherical and finite, but eternal (no beginning and no end) Earth spherical; much smaller than stars Aristole believed in three kinds of motion: rectilinear, circular and mixed; each planet followed own specific path Hierarchical model of the universe greatly influenced later medieval scholars Contribution to astronomy: ability to ask certain questions about the universe and stimulate others who came for answers A4
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A5
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6. Aristarchus ( 310-250 BC ) “Magnitudes and Distances” Heliocentric Theory 6 planets move in simple circles at uniform rates; rates differ for each planet; rates and distances determined from observations (strikingly similar to modern view) Attempted to calculate Sun-Earth distance (method actually pretty good) Two issues contribute to discredit him: #1 Other astronomers tried to use his model to predict the future position of Mars (We know now that orbits only slightly different from circles produce large angle prediction errors.) Besides, Greeks obsessed with circles #2 Arrival of Hipparchus 7. Hipparchus (190 BC -120 BC) B orn in Nicaea (now Iznik, Turkey) Observer; greatest astronomer of antiquity Developed science of spherical trigonometry Located position on
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Notes_A%20BP - A1 History Development of celestial...

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