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B Where on Earth someone is

  1. Jun 1, 2018 #1
    I saw the following question in Yahoo Answers,

    Is it even possible to know this?
     
  2. jcsd
  3. Jun 1, 2018 #2

    russ_watters

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    If you have the time in UTC, sure.
     
  4. Jun 1, 2018 #3

    DrClaude

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    But with what error bars?

    If you have no orientation information (which way is North?), then there is quite a wide band of longitude+latitude solutions, mirrored on each hemisphere.
     
  5. Jun 1, 2018 #4

    russ_watters

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    Accurate enough to navigate a ship in the 19th century...
    Good point; you would have to know the hemisphere, which maybe you could see from context in the photo.
     
  6. Jun 1, 2018 #5

    DrClaude

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    Not without a compass :smile:

    My point is that at any given time, the same stick length will give the same shadow length at many points on the globe. If you have no information on the orientation of the shadow, there is not much you can say.
     
  7. Jun 1, 2018 #6

    russ_watters

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    Oh, you don't just mean the hemisphere. Yes, I see you're right; to get the longitude from the azimuth of the sun, you need the actual angle from north.

    and...now that I think about it, without longitude (and with it local time) first, the altitude doesn't tell you latitude either.
     
  8. Jun 1, 2018 #7

    jbriggs444

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    The azimuth just positions you somewhere on a circle that is centered on a point where the sun is directly overhead. A compass heading could position you on that circle.

    Edit: if the ground is not level, your navigation could be way off.
     
  9. Jun 1, 2018 #8

    sophiecentaur

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    The one with the penguins in, perhaps.
     
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