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    An interesting question
    From: Lu Abel
    Date: 2013 Oct 10, 11:19 -0700

    from a student in my celestial navigation class:
    If one were on the Great Plains (of the US, for our non-US members)
    could one take a sextant shot and get a LOP with reasonable accuracy?
    The Great Plains are a vast area of what appears to be totally flat land.
    My first instinct was (and still is) to say "no."   I don't believe the
    human eye could distinguish a one degree slope in the ground, and so the
    Great Plains easily could undulate.
    But I also wondered if I were lost in my covered wagon with nothing but
    a sextant and a Nautical Almanac, could I get a reasonable LOP?
    I've driven from St Louis to Denver.  You cross vast areas of what
    appears to be totally flat ground ("on a clear day you would be able to
    see Pike's Peak except for the curvature of the earth" was a saying when
    I was a student at the University of Illinois).
    Let's assume it's truly flat ground.   Back of the envelope, the
    distance is 1000 miles and the elevation gain is one mile.   That's a
    right triangle with a hypotenuse of 1000 and an opposite side of 1.
    Sine of a small angle is approximately equal to the angle itself
    expressed in radians.   So the angle is 1/1000 radians or 3.5 minutes of
    Assuming no undulation in the ground, getting a LOP that's off by 3.5
    miles ain't bad.

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