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    Re: Refraction
    From: Frank Reed CT
    Date: 2005 Aug 16, 14:17 EDT

    Marcel you wrote:
    "Probably one should  calculate refractive index for the dominant wavelength
    depending on the  object's zenith distance?"
    Depends on your goal. If you're trying to  portray the appearance of stars at
    very low altitudes in the atmosphere, then  you should calculate refraction
    for each color of the spectrum (split up as you  choose). When you see stars
    very low in the sky, they do, in fact, look like  little "French flags" because
    the red light is refracted more than the blue  light. For navigational
    purposes, this is irrelevant, but for the project you  briefly described earlier it
    might be interesting to include. But be sure to  include extinction. NO stars
    are visible to the unaided eye right at the horizon  since the extinction is on
    the order of twelve magnitudes. Fortunately, if you  do a proper numerical
    integration for refraction, you get the extinction "for  free".
    42.0N 87.7W, or 41.4N  72.1W.

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