ASTR1 - MotionsofthePlanets 26/08/200912:20:00...

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Motions of the Planets 26/08/2009 12:20:00 Geocentric Model Aristotle build a geocentric model used for centuries Ptolemy built a mathematical model of the solar system Problem was it couldn’t explain retrograde or pattern of mars movement o Prograde  is normal direction of movement,  retrograde  is when  something moves backyard o Mars does retrograde often, sometimes looks like zig-zag or loop  depending on year o Retrograde takes several weeks to complete o Jupiter is currently in retrograde In order to correct the model for retrograde epicycles were created o Even though complicated, it predicted excellently Copernicus Believed that the geocentric model shown motions that were to complicated  to be reality Geocentric model doesn’t explain retrograde motion Built the first mathematical heliocentric system Inferior planets o If planet is between earth and sun it is at inferior conjunction (new) o If planet is farthest from earth it is at superior conjunction (full) o (if above horizon, farther west of sun   great western elongation) o an never see an inferior planet at midnight (view within a couple of  hours of when sun is rising or setting)
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o Superior planets o Orbit lies outside earth’s orbit o Opposition is when planet is outside of earth (full, at midnight) o Conjunction is when planet is closer to sun than earth (new, noon) o Closer to the sun, the shorter the distance traveled and the faster the planet  moves
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o Therefore, Earth moves faster than Mars, and Mars appears to move  backwards, and then it seems to start moving forward again   purely  perception o When Mars starts retrograde it must be close to opposition o Retrogrades always start around opposition Heliocentric model Copernicus insisted that the heavens were perfect, therefore the planets  moved in perfect circular orbits about the Sun Shown simple explanation for retrograde Failed to explain why planets move faster across the sky at particular  locations along their orbits Ended up adding epicycles as correction Galileo Galilei First to build astronomical telescope Observed mountains and craters on the Moon Observed spots on the Sun o Sun spots o Noticed that sun spots rotate Discovered the four largest satellites of Jupiter o Called Galilean Moons Observed the phases of Venus Phases of Venus Support Heliocentric Model Full at superior conjunction. New at inferior conjunction Venus has largest angular diameter at new phase because its closer to Earth
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Tycho Brahe Firm believer of geocentric model Best naked-eye observer known
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This note was uploaded on 09/13/2011 for the course ASTR 1002 taught by Professor Campell during the Spring '11 term at LSU.

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ASTR1 - MotionsofthePlanets 26/08/200912:20:00...

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