RE: Violet Satellite Appearance

From: Ted Molczan (
Date: Tue Aug 10 2010 - 11:55:03 UTC

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    Chris Zietkiewicz wrote:
    > Jim, thank you for confirming the ID.  Interesting that you note a 4.2
    > brightness but when I run HA this morning I get 3.2.
    Your comment prompted me to analyze Russell Eberst's 26 brightness observations of Spot 5, with the
    aid of the following plot of magnitude normalized to 1000 km versus phase angle:
    I estimate standard magnitude = 5.9 +/- 1.5 (1000 km, 90 deg phase angle). Coefficient of phase =
    0.02 mag/deg. The three brightest observations may have been specular reflections; removing them
    would not greatly affect the results, mainly reducing the uncertainty. The data set is somewhat
    small, but I believe the results are reasonable. Heavens-Above standard magnitude for this object is
    3.7, which is at variance with the above plot.
    My standard magnitude predicts mag 5.6 at the start of your exposure, increasing to 5.9 by the end,
    both +/- 1.5. Jim's estimate of 4.2 is at the brightest end of the range, perhaps indicating a
    specular reflection.
    I hope to some day produce a set of standard magnitudes for all objects for which there are
    sufficient observations, that would include coefficient of phase, the range of uncertainty, and the
    number of observations used in the analysis. I suspect that predictions of the majority of the
    previously analyzed objects would not change significantly, but knowing the uncertainty range would
    be valuable. In the meantime, observers should allow for at least 1 mag uncertainty in magnitude
    Ted Molczan
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