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Parallax and Perspective Explained

  1. Sep 22, 2011 #1
    I completely understand the effects of parallax as well as perspective...intuitively; but I can't seem to explain them to a particularly inquisitive child I'm tutoring.

    He wants to know, in conceptual terms, why objects in the distance like the moon seem to move in the same direction as you (the moon is following me!), while close objects seem to move in the opposite direction to one's movement.

    He also wants to know, again in conceptual terms, why things in the distance look smaller and why lines seem to converge. I told him it's because objects subtend a smaller angle the further away they are, but he wasn't satisfied with my admittedly under-thought answer.

    Any help in explaining and understanding this would be greatly appreciated. Thank you!
  2. jcsd
  3. Sep 22, 2011 #2


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    the best I can do is:

    your field of view expands as you look further into the distance, the more area your field of view covers the smaller objects seem as a result, as for the moon following him, the further things are the less they seem to move when you move, the moon is so far away that it's movement is unnoticable, however when compared to closer objects that move away from you this would make it appear that the moon is moving with you, (perhaps you could ask him next time he is in a train to compare the speeds of trees in the distance and trees that are closer to the train)

    that's the best I can do, I'm not sure if it will be helpful or not
  4. Sep 23, 2011 #3


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    I'd say the answers you gave him were pretty good. If he doesn't accept them then I think you should simply tell him that the way you explained it is the way science does and that while it might not make any sense, it is the correct answer. Many people have a hard time accepting things initially, but once they mull it over in their head or learn a little bit more it simply "clicks" and starts to make sense.
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