RE: accuracy of ISS / Venus transit track

From: Matson, Robert (
Date: Thu Jun 03 2004 - 20:41:16 EDT

  • Next message: Denis: "Re: accuracy of ISS / Venus transit track"

    Hi Tom,
    Have been following your updates on the ISS/Venus transit for
    next week, and thought I'd point out one factor that should
    simplify your analysis.  In one of your recent posts, you wrote:
    "Atmospheric ray-bending would have the effect of moving the shadow
    in the direction of the ISS; effectively equivalent to increasing
    the observer's elevation above sea-level by 75 meters, in this case
    (which, given a range of 839 miles, would not be very significant)."
    There is no need to complicate your analysis by computing refraction.
    For a ground-based observer, refraction will bend the light rays
    from the Sun, Venus and ISS by equal amounts.  Thus, the apparent
    position of ISS relative to the Sun/Venus would be identical, even
    if the earth had no atmosphere.
    By far the greatest source of uncertainty in the ISS transit calculation
    is the accuracy of the TLE itself.  For example, one big solar outburst
    in the next day or two would change all your predictions.
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