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    Re: How far is polaris?
    From: Fred Hebard
    Date: 2007 Nov 22, 12:10 -0500

    If you could expand on the speed of light business, that would be great.
    On Nov 22, 2007, at 5:49 AM, frankreed@HistoricalAtlas.net wrote:
    > 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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