Earth Shadow at Geosync Orbit

From: Jeff Umbarger (
Date: Tue Feb 27 2007 - 17:16:23 EST

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    Hey All,
         Could someone provide to me the Earth's two
    shadow edge points at the Clarke Orbit for Feb 27 at
    4:00UT, 6:40UT, and 8:00 UT in RA and Dec? This is for
    +33.069N and -96.768W. And if I could be so pushy,
    could I also have those 12 numbers for tonight, Feb 28
    at those same times?
         I'm seeing a very interesting geosat flare
    phenomena. With the earth's shadow chord length so
    short on across the Clarke Orbit (Geosat flare season
    began at 16:28UT Feb 26 by my calculations) there is
    an opportunity for geosats to be directly below or
    above the anti-solar point and *not be eclipsed* by
    the earth's shadow - only when the anti-solar RA has
    moved an hour beyond (or before) local midnite.
         I watched at 8UT Feb 27 (1hour and 20min after my
    local midnite) the XM constellation light up just as
    the anti-solar RA passed through them. I belive the
    earth's shadow was much farther to the right (west)
    then I had expected. This was spectacular! I've gotten
    a picture of two of these satellites flaring before,
    but I looked up and saw 4 or 5 of them within 15 arc
    minutes - all visible without binocs! Thanks for any
    help with these 12 (or 24!) numbers.
              Jeff Umbarger
              Plano, TX USA
              CST (GMT-6)
    P.S.: I will be following up shortly with my seasonal
    geosat flare graphical calculator (if I can bug Kevin
    to host this again! Sorry Kevin!)
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