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Homework Help: Parallax angles

  1. Jun 26, 2011 #1
    1. The problem statement, all variables and given/known data
    Can someone please explain to me how parallax works?
    I don't understand how the angle of parallax is measured

    Question to help: Astronomers measuring the parallax angle to Planet X found that the angle measured after 6 months was 1.52 arcsec different from the initial measurement

    Angle theta is angle (Earth-Jan)-Star-(Earth-July)

    They then said that angle theta is 1.52 BUT I don't see how, can someone please provide a diagram
    2. Relevant equations
    I can complete question knowing the angle theta is 1.52. I just don't understand why it is 1.52

    3. The attempt at a solution
    as above
  2. jcsd
  3. Jun 26, 2011 #2


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    Hold your thumb out at arm's length with a distant wall in the background. Close one eye and then the other. See how your thumb seems to move back and forth depending on which eye you are looking through? That's the basic idea of parallax. By measuring how much you thumb moves back and forth, and knowing the distance between your eyes, you can calculate the length of your arm ( I know, big deal!)
  4. Jun 26, 2011 #3
    can you draw the diagram for the Question about planet X
  5. Jun 26, 2011 #4


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  6. Jun 26, 2011 #5
    the thing I don't get is "1.52 arcsec different"
    I can't visualise this in my head
  7. Jun 26, 2011 #6
  8. Jun 27, 2011 #7


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    They (the astronomers) measured the angle to be 1.52". To measure an angle this small takes a tremendous amount of skill and care.

    For the right triangle they draw, 1.52" corresponds to 2θ .
  9. Jun 28, 2011 #8
    I don't have a problem with the angle they measured BUT the difference between angle in Jan and angle in Jun is 1.52, so surely the paralax angle is 1.52 + original angle
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