RE: Iridium flare elevation

From: Matson, Robert (
Date: Thu Aug 09 2001 - 16:21:10 PDT

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    Hi Steve and List,
    > What is the highest elevation for a major iridium flare of -6 or better
    > the sun at between 0 and -5 on the horizon? My latitude is +39 . I have
    > seen a couple of daytime flares, but a -8 with dark skies is incredible.
    At 39 degrees north, your highest elevation flare exceeding
    magnitude -6 can theoretically exceed 70 degrees elevation.
    However, these can only occur just before sunrise or just
    after sunset.  You're better off with higher contrast -- i.e.
    darker skies at the expense of a few degrees of elevation.
    The inverse square law won't hurt the brightness much, if
    at all, since it can be compensated by the cosine projected
    area factor for the MMA.
    If you relax the elevation angle constraint to 50 degrees,
    there are a number of -6 or brighter flares that occur
    under much darker skies.  These will always be descending
    node passes in the predawn hours for passes in late-June
    to early August (left MMA), and ascending passes in predawn
    hours for late November to mid-January (right MMA).
    -6 or brighter evening flares, when the flare elevation exceeds
    50 degrees, occur from the very end of March to mid-April, and
    the first half of September (though early morning -6 flares are
    also possible in mid-September).  These evening bright flares
    above 50-degree elevation are always descending node passes.
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    This archive was generated by hypermail 2b29 : Thu Aug 09 2001 - 16:23:49 PDT