Re: Geosat Flare Question

From: Ed Cannon (ecannon@mail.utexas.edu)
Date: Fri Oct 17 2003 - 04:01:36 EDT

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    Jeff Umbarger wrote:
    
    >     Location: 33.0695N, 96.7681W
    >     Timezone: CST/CDT (GMT -5)
    > 
    >     ... 2 nights ago (Wednesday October 15 at 00:43 CDT) I 
    >noted a "star out of place" just north of the constellation 
    >Cetus. It made a near perfect equilateral triangle with 
    >theta and eta Cetus.  ...  Last night I saw, I believe the 
    >same ones at 00:31, 01:22 (a cluster of 3 or more), and 
    >01:50. 
    
    Working backwards from the cluster at 1:22 Oct 16 CDT being 
    three or four of these six:
    
    22930 93-078A DirecTV 1     
    23192 94-047A DirecTV 2     
    23553 95-019A AMSC 1 (always the faintest when seen from here)
    25937 99-056A DirecTV 1-R   
    25954 99-060A GE 4          
    26985 01-052A DirecTV 4S    
    
    it seems that the RA is roughly 1:12-14 (2000).  If so, then
    the one at 1:50 probably was Anik F1 (00-076A, 26624).  If 
    the position can be shifted a little, it looks like the one 
    at 0:31 was Telstar 402R (95-049A, 23670), although I wonder 
    if it might have been Galaxy 11 (99-071A, 26038), as it is 
    one of the often extra-bright ones.  At 0:31 it was at about
    RA 1:08.
    
    I want to say that the one at 0:43 CDT the previous night 
    was Galaxy 11, although with Highfly it's in eclipse by 
    then.  Brasilsat B4 (00-046A, 26469) seems to be in the 
    right place, but because it's spin-stabilized, I tend to 
    doubt it's the one.  Nimiq 1 (99-027A, 25740) is always 
    fainter than Galaxy 11 when seen from here, and it also was 
    in shadow at 0:43 according to Highfly.
    
    >1.) [Rainer Kresken] states that best time to see these 
    >flares is when the geosat is less than 25 degrees above the
    >horizon. Why? 
    
    I believe the theory on this is that the flaring effect 
    tends to be more pronounced when the observer, as seen from 
    the satellite, is closer to the Earth's limb, which makes 
    the geometry more favorable than when the observer is 
    farther from the limb.
    
    >2.) I've calculated the ring of geosats to be at -5.45
    >degrees declination for my latitude. So when the earth's 
    >shadow is south of the celestial equator (before autumnal 
    >equinox), the eclipsing should be optimal for me. But 
    >Rainer's table of optimum dates for latitudes shows the 
    >farther south before equinox and farther north after 
    >equinox. Could someone explain this better?
    
    I believe the theory here is that the geometry is most 
    favorable when the satellites are actually going through 
    the Earth's shadow, and the flaring happens just before and 
    after shadow entry.  You have to figure out the angles from 
    Sun to satellite and back to your position on the Earth.  
    
    Now, there's something else.  Each season in the last four
    years I've been able to see with 10x50 binoculars some of
    them in the "wrong" position, about three hours before 
    shadow entry.  Galaxy 11 and Anik F1 are two of those.  
    (XM-1 and XM-2 are the same model satellite as Galaxy 11 
    and Anik F1, along with one of the PAS's much farther 
    east.)  Also, I've seen GE 3 (97-050A, 24936) easily with 
    binoculars in the "wrong" place, even though it's a 
    different model of satellite.  I've been able to see three
    of these the last three nights even though the season 
    should be over for this latitude (30 north).
    
    You didn't mention how you were observing -- what equipment.
    
    Welcome to the flaring geosat observers club!
    
    Ed Cannon - ecannon@mail.utexas.edu - Austin, Texas, USA
    
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