astronomy chapter 4

  1. heliocentric universe
    a model of the universe with the sun at the centerm, such as the Copernican universe
  2. uniform circular motion
    the classical belief that the perfect heavens could only move by the combination of uniform motion along circular orbits
  3. geocentric universe
    a model universe with Earth at the center, such as the Ptolemaic universe
  4. parallax
    the apparent change in position of an object due to a change in the location of the observer
  5. retrograde motion
    the apparent backward (westward) motion of planets as seen against the background of stars
  6. epicycle
    the small circle followed by a planet in the Ptolemaic theory. The center of the epicycle follows a larger circle around the earth
  7. deferent
    in the Ptolemaic theory, the large circle around Earth along which the center of the epicycle was throught to move
  8. equant
    • in the Ptolmaic theory
    • the point off center in the deferent from which the center of the epicycle appears to move uniformily
  9. paradigm
    a commonly accepted set of scientific ideas and assumptions
  10. ellipse
    • a closed curve around two points called the foci
    • the total distance from on focus to the curve and back to the other focus remains constant
  11. mass
    • a measure of the amount of matter making up an object
    • weight is a measure of the gravitational force acting on an object
  12. circular velocity
    the velocity an object needs to stay in orbit around another object
  13. closed orbit
    • an orbit that returns to the same starting pint over and over
    • either a circular orbit or an elliptical orbit
  14. escape velocity
    the initial velocity an object needs to escape from the surface of a celestial body
  15. open orbit
    an orbit that carries an object away, never to return to its starting point
Card Set
astronomy chapter 4
key terms and concepts: the birth of astronomy