Ptolomy, copernicus, and kepler's laws

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Ptolomy, copernicus, and kepler's laws

  1. 1. Models of the Solar System
  2. 2. Some early mythology described the Earth as flat. <ul><li>If you sailed to the end you would fall off! </li></ul>
  3. 3. Ptolomy <ul><li>*Ptolomy (90–168) lived in the time of the ancient greeks. </li></ul><ul><ul><li>*Described a geocentric solar system </li></ul></ul><ul><ul><li>*Supported by Aristotle </li></ul></ul><ul><li>*Two common observations supported the idea that the Earth is in the center of the Universe </li></ul><ul><ul><li>*the stars, sun, and planets appear to revolve around the Earth each day, with the stars circling around the pole and those stars nearer the equator rising and setting each day and circling back to their rising point </li></ul></ul><ul><ul><li>*Earth is solid and stable it is not moving—but is at rest </li></ul></ul>
  4. 4. Ptolomy <ul><li>Astronomers observed that the planets moved a little differently than stars </li></ul><ul><li>Occasionally a planet, particularly Mars, would reverse direction for a while and then resume motion in it’s original direction. We call this back and forth motion “retrograde” motion. </li></ul><ul><li>Mars in retrograde </li></ul>
  5. 5. Ptolomy <ul><li>How can this be explained?!? Epicycles </li></ul>
  6. 6. Ptolomy <ul><li>The Ptolemaic order of spheres from Earth outward is: </li></ul><ul><li>Moon </li></ul><ul><li>Mercury </li></ul><ul><li>Venus </li></ul><ul><li>Sun </li></ul><ul><li>Mars </li></ul><ul><li>Jupiter </li></ul><ul><li>Saturn </li></ul>
  7. 7. Copernicus <ul><li>Nicolaus Copernicus (1473 –1543) was the first astronomer to formulate a comprehensive heliocentric cosmology </li></ul><ul><li>Heliocentric means sun-centered </li></ul><ul><li>Carl Sagan on Ptolomy and Copernicus </li></ul>
  8. 8. ’ S LAWS
  9. 9. Tycho Brahe <ul><li>His observations of planetary motion, particularly that of Mars, provided the crucial data for astronomers like Kepler (1571-1630 ) to construct our present model of the solar system. </li></ul>
  10. 10. KEPLER’S 1 st LAW <ul><li>All planets orbit the sun in elliptical paths with the sun at one focus. </li></ul>
  11. 11. What is an ellipse?
  12. 12. Ellipses can have different shapes
  13. 13. Eccentricity <ul><li>The more “flattened” an ellipse is, the larger its eccentricity. </li></ul>
  14. 14. KEPLER’S 2 nd LAW <ul><li>A planet sweeps out an equal area of </li></ul><ul><li>space in an equal amount of time. </li></ul>
  15. 15. Faster at perihelion or aphelion? Perihelion: Faster Aphelion: Slower
  16. 16. KEPLER’S 3 rd LAW <ul><li>P 2 = # of solar masses </li></ul><ul><li>a 3 </li></ul><ul><li>For our sun p 2 /a 3 = 1 </li></ul><ul><li>Where P stands for the period, or time to go around once, </li></ul><ul><li>and a stands for the semi-major axis </li></ul><ul><li>P must be in years, while a must be in AUs </li></ul><ul><li>Carl Sagan on Ptolomy and Kepler </li></ul><ul><li>Tycho Brahe , Johannes Kepler and Planetary Motion (1 of 2) </li></ul>

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