AST005 Exam 2 review

AST005 Exam 2 review - ASTRO 5 Richards The Sky and Planets...

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1 ASTRO 5 - Richards The Sky and Planets Mid-term 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.

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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: planet-Sun 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 Sun-planet and planet-planet distances Measure " (greatest elongation) Sun - Mercury distance, d S-M = sin " - measured relative orbital speeds of planets inner planet revolves faster than outer planet d S-M " 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

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4 Kepler’s Second Law the planet-Sun 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 - semi-major axis (AU) - 3 laws
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