Re: A bright double

From: Gerhard HOLTKAMP (grd.holtkamp@t-online.de)
Date: Tue Nov 02 2010 - 21:00:56 UTC

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    On Tuesday 02 November 2010 02:42, Bram Dorreman wrote:
    > Here is the easily readable version:
    > I saw this brilliant pair TerraSarX (2007-026A) and TandemX (2010-030)
    > on the same pass as  Gerhard Holtkamp. From my location they were at
    > brightest at about 17h 28m 23s at RA 17h 04m dec +40 deg, Az 266 deg,
    > alt 58 deg. There magnitudes were +0.1 and +0.3.
    >
    
    Thank you for repeating your observation in an easily readable version (I 
    actually had noticed your original report but only accidentally!). Brad Young 
    also seems to have observed the double.
    
    > Then I started calculating and found that after 11 days the orbit and
    > satellites have the same position with respect to the observer.
    > I expect to see this "golden pair" again (if weather permits) on November
    > 5th.
    >
    
    That is correct. Checking the information on TerraSarX on the DLR website I 
    found a remark that the orbit is an exact 11 day repeat cycle. So every 11 
    days the two satellites will pass across the sky in the same way. But there 
    are two things to consider with regards to flares:
    The sun will have shifted slightly between the two days so the geometry of 
    illumination will be a little different (I observed something like that with 
    MetOp-A flares between the end of August and the beginning of October this 
    year. MetOp-A is in a 5 day sub-repeat cycle and I could see flares every 5 
    days but each time the position had shifted a little and the magnitude also 
    varied between the different flares.) 
    Also I'm not sure whether TerraSarX and Tandem X always keep their attitude or 
    whether they change the attitude to make the radar antenna point differently 
    to look at some other target. So we will have to keep observing as many 
    passes as possible to find out. 
    
    Gerhard HOLTKAMP
    Darmstadt, Germany
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