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Unformatted text preview: 1 ASTRO 5  Richards The Sky and Planets Midterm Exam  Review 2 Babylonians : length of year, time, angular measurements Ancient Greeks : named the constellations Thales : Need to understand the universe Pythagoras : Earth is round circular motions Plato : circular motions Aristotle : physical laws govern universe geocentric view proof that Earth is spherical Eratosthenes : accurate size of Earth Aristarchus : heliocentric view (since Sun larger than Earth) Hipparchus : catalog of stellar positions discovered precession invented system to measure stellar brightness could not measure stellar parallax ( to prove heliocentric theory) (Parallax was first measured by Bessel in 1838) Ptolemy : used epicycles to explain motions of planets Early Astronomers 624 B.C.E.  200 C.E. 2 Copernicus : measured relative positions and motions of planets believed in heliocentric theory Brahe : accurate observations of planets Galileo : reasons to support heliocentric theory  phases of Venus  changing angular size of Venus measured acceleration due to gravity Modern Astronomers Kepler : Law 1: orbits of planets are ellipses Law 2: planetSun line sweeps out equal areas in equal times Law 3: P 2 = a 3 Newton : Law 1: inertia Law 2: acceleration, a = F net / m Law 3: action and reaction forces Universal Law of gravitation: F = GMm/d 2 Weight: W = mg surface gravity, g = GM/R 2 escape velocity, V esc = ! (2GM/R) conservation of angular momentum Nicolaus Copernicus adopted heliocentric view (Sun is largest body ! center)  calculated Sunplanet and planetplanet distances Measure " (greatest elongation) Sun  Mercury distance, d SM = sin " measured relative orbital speeds of planets inner planet revolves faster than outer planet d SM " Mercury Earth 3 Lighter ball h Heavier ball h He rolled metal balls down an inclined plane and found that g = 9.8 m/s 2 Galileo discovered that all objects fall at the same rate. This rate is called “ the acceleration due to gravity ” (g) Johannes Kepler adopted heliocentric view  devised 3 laws using Brahe’s observations First Law the orbits of all planets are ellipses with the Sun at one focus foci ellipse : a closed curve defined by a fixed total distance from 2 points (foci) major axis (2a) minor axis (2b) eccentricity, e: e 2 = 1  (b 2 /a 2 ) circle: e = 0 line: e = 1 4 Kepler’s Second Law the planetSun line sweeps out equal areas in equal times Sun perihelion fastest aphelion slowest Kepler’s Third Law P 2 = a 3 P  sidereal orbital period (years) a  semimajor axis...
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This note was uploaded on 01/11/2012 for the course ASTRO 005 taught by Professor Janecharlton during the Fall '09 term at Penn State.
 Fall '09
 JANECHARLTON

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