Models of the Planets

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Models of the Planets

• Lorin Walls
• Physics 001

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Plato

• Plato gave his students an assignment
• Make a model of the planets to explain the
  motions we see in the sky.
• The guidelines were as follows
• It had to be a combination of perfect circles
• Must use simple ideas
• Must concur with observations
• And it must be a model
• If Plato had excluded the guideline stating the
  model must be a combination of perfect circles,
  the correct model would have been found a lot
  sooner.

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Eudoxus Platos student (4th Century B.C.)

• Geocentric
• Crystalline spheres
• 26 spheres to account for all the motions of the
  sun, moon, stars, and planets

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Hipparchus Platos student (4th Century B.C.)

• Geocentric
• Deferents and epicycles explained the retrograde
  motion
• Deferent main sphere of the planets, centered
  on the Earth
• Epicycle minor sphere of planets that is
  attached to the deferent
• This explains retrograde motion
• Explains varying brightness of the planets

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Aristarchus (270 B.C.)

• Sun is at the center! (heliocentric)
• Planets and moon all orbit Earth
• This was ruled out for 3 reasons.
• The Earth rotating could not be accepted because
  you cant necessarily feel the motion.
• Lack of parallax nearby stars would appear to
  shift with relation to other stars
• Earth at the center is much more appealing.

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Claudius Ptolemeus (150 A.D.)

• Earth is slightly off center (eccentric)
• Explains varying brightness of the planets and
  seasons
• Uses deferents and epicycles
• Unchallenged for 2,000 years

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Nicolaus Copernicus (1500s)

• Challenged Church doctrine and reintroduced the
  heliocentric theory
• Used plethora of epicycles and deferents
• Very complex model

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Tycho Brahe (1580s)

• Measured positions of planets and sun with
  accuracy, disproving detectable parallax

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Kepler (1600s) Student of Tycho

• Used ellipses instead of circles for orbits, NOT
  epicycles
• Eliminates use of epicycles and deferents

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Galileo (1620s)

• Destroyed the idea of a perfect universe with the
  following findings
• Spots on the Sun
• Mountains and seas on the Moon (maria)
• The Milky way is made of many stars.
• Venus has Phases
• Jupiter has moons

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New Insight

• Knowing the process astronomers went through to
  figure out our solar system and how wrong they
  were makes me think about the things we are
  researching know. Are we far from the true
  answers but think were close just like the
  astronomers?

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• This is what our solar system looks like on
  December 7, 2007 at 2200.

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Sources

• http//zebu.uoregon.edu/js/ast221/lectures/lec06.
  html
• http//www.fourmilab.ch/cgi-bin/Solar
• http//home.nycap.rr.com/mismedia/CR/Image23.gif
• http//images.google.com/imgres?imgurlhttp//www.
  candleinthedark.com/geocentric.gifimgrefurlhttp
  //www.candleinthedark.com/copernicus.htmlh199w
  231sz23hlenstart10um1tbnidjFM-8J2IdS1ZBM
  tbnh93tbnw108prev/images3Fq3Dcopernicus2
  Bmodel2Bof2Bthe2Buniverse26svnum3D1026um3D1
  26hl3Den26sa3DN
• http//www.shef.ac.uk/physics/people/vdhillon/teac
  hing/phy105/ptolemy.gif
• http//www.math.nus.edu.sg/aslaksen/projects/heilb
  ron/images/Hippar45.jpg
• http//www-astronomy.mps.ohio-state.edu/pogge/Ast
  161/Unit3/Images/eudoxus.gif