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    Re: How far is polaris?
    From: Frank Reed
    Date: 2007 Nov 22, 05:49 -0500

    Mike (Isonomia) wrote:
    "In other words, A2 accounts for the finite distance of the star! That is to
    say, the star wobbles with respect to the background galaxies (can't say
    stars because they are too near!!!)
    
    It is absolutely mind boggling to think that a handheld instrument like a
    sextant could possibly be affected by the distance to the stars.
    
    It completely turns history on its head. ..."
    
    Aw, sheesh, Mike. Don't go turning history on its head before you've
    understood the basics. :-)  No, A2 is not connected with the distance to
    Polaris --more than one post has tried to explain this to you further. Let's
    work the numbers... The nearest stars are on the order of ten lightyears
    away (of the bright navigational stars, there are two closer). How does ten
    lightyears compare with the distance to the Sun? Well, that's easy enough if
    you remember that the distance to the Sun is very close to eight
    lightminutes. Compare eight minutes with ten years... Now, the parallax of
    the Sun is a minor, though not necessarily negligible, correction in
    celestial navigation amounting to only 9 seconds of arc. The parallax of the
    stars, even the nearest, is less important by the ratio of eight minutes to
    ten years. I'll let you work the math. Clearly, it's a completely trivial
    factor for celestial navigation with a handheld sextant.
    
    But there is an extraordinary effect that you can detect with a handheld
    sextant, if you're a careful observer, that might surprise you. It's the
    speed of light. Aberration of star light --directly due to the finite speed
    of light-- can be detected by observing, very, very carefully, the angular
    distances between stars over the course of a year. Your Ebbco isn't up to
    the task, but a well-adjusted metal sextant is. And isn't that a bit
    amazing: you can measure the speed of light (to one significant digit) using
    a handheld instrument.
    
     -FER
    
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