Re: Brightness of GRACE Satellites

From: Gerhard HOLTKAMP (grd.holtkamp@t-online.de)
Date: Sun Oct 29 2006 - 17:04:56 EST

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    Bram Dorreman wrote:
    
    >Most transits of GRACE Satellites result in steady appearing satellites.
    >Sometimes the conditions are suitable to let the two spacecraft show
    >one flare. I did not analyse those special cases. But I presume that
    >there might be a connection: GRACE's azimuth equals Sun's azimuth. I
    >did not prove this yet.
    >When one speaks about variable satellites, what does one mean?
    
    >Therefore my question: how many brightness variations were actually seen?
    
    Looking at the pictures they sent me it looks like there were two peaks in 
    brightness (with different strength) of the leading satellite in the first 
    picture and the trailing satellite shows up strongly on the first picture and 
    much weaker at the second picture but at different positions than the leading 
    one. The visual report mentioned the trailing satellite as being distinctly 
    brighter than the first one which disappeared much sooner. So on that 
    particular pass (19:02 UTC, 16-OCT-06) there seems to have been a difference 
    in attitude between the pair.
    
    Today I observed a pass of the GRACE pair from my place (49.88N, 8.66E) when 
    they appeared low in the western sky at 18:47/ 18:48 UTC (29-OCT-06). Almost 
    due West they appeared bright at about mag 2 at identical positions  before 
    slowly fading. As the ideal flare surface would have been oriented less than 
    5 deg away from the nadir this was probably caused by the flat underside 
    (which I think they have). So they definitely looked absolutely regular and 
    perfectly controlled tonight.
    
    Gerhard HOLTKAMP
    Darmstadt, Germany
    
    
    
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