Telescopic Observation of ISS/Color Variations

From: Cees Bassa (c.g.bassa@phys.uu.nl)
Date: Wed Dec 20 2000 - 12:28:05 PST

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    Hello List,
    
    Below is a report on a telescopic observation of the ISS I did today. The 
    station made a 78 pass,
    the first since the arrival of the P6 truss. You can read the entire report 
    with drawings at:
    http://www.astro.uu.nl/~bassa/astro/temp/iss.htm
    
    There are some things I noticed. First it struck me how easy it is to 
    observe the actual shape of
    the station. I was able to distinct the solar arrays as separate and of 
    course the orange color of it.
    
    Second, I didn't observe the solar arrays after culmination. I did observe 
    them before culmination, but I lost the satellite because my telescope ran 
    into the tripod leg while I was manually tracking
    the ISS. After I reaquired the satellite the orange color was gone and I 
    wasn't able to see the
    solar arrays anymore, just the grey/white modules of the station.
    
    It does seem plausible to me that because of a change in the angle 
    observer-station-sun caused
    the solar arrays to disappear. It is seen in several pictures taken from 
    STS97 that the newly solar
    arrays appear orange in one picture and black in another, depending on the 
    orientation of the station, observer and sun.
    
    What does amaze me is that I haven't heard from any reports mentioning a 
    change in color of the
    station during a pass, while it seems so logical. To me it also seems 
    pretty easy to model and
    predict how the color and brightness depend on time and place for any 
    observer on Earth as long
    as one knows the reflection characteristics of these solar arrays. They 
    shouldn't be to hard to
    deduce if enough observations are being made.
    
    Regards,
    	Cees Bassa
    
    P.S. I would advice any person owning a telescope to take a telescopic look 
    at the ISS. It really is
    very awesome to see something with a shape flying along the stars. It's not 
    hard to track the
    station manually, though some practice is handy.
    
    REPORT:
    
    The first time I observed the station after the arrival of the new solar 
    arrays was on December 18 when the Netherlands were favoured again with 
    passes of the satellite. It struck me the station was that orange. I had 
    read reports of other observers on it, but I hadn't expected it to be so 
    easy to distinct. I observed it again on December 19.
    
    For December 20 a pass of 78 high was predicted. For an overhead pass of 
    90 the stations distance will be it's altitude of approximately 370 km. 
    For a culmination altitude of 78 the distance will be some 380 km minimum.
    I had observed both the ISS and Mir through a telescope before, but I was 
    never able to see any details except an elongated streak of light. So I 
    expected nothing this time.
    I was pretty busy that evening so I didn't have much time to setup my 
    telescope, which made it a bit difficult to obtain the station through the 
    the telescope when I came over, but when I got it in the 40x magnifaction 
    field I immediately saw the T-shapedness of the object.
    
    Looking more carefully while manually following and finding best focus I 
    could spot the two orange solar arrays seperately with the station as a 
    greyish-white streak extending from the within the arrays. They were 
    elongated stripes as in the left drawing at the top of this document.
    
    It was difficult to keep up the stations motion when it got at high 
    elevations above the horizon and I lost it when my focusing tube hit one of 
    the tripods legs. I had to swing the telescope to the other side of the 
    RA-axis and reaquire the station again.
    
    I found the station pretty fast, at an elevation of some 65-70. As seen 
    throught the telescope it had decreased in brightness and the two orange 
    solar panels were not visible any more. Probably because of the angle 
    between the sun, the station and me now it has passed my local culmination 
    point. One thing that noticed was that the stations color was more grey 
    instead of the white color it had before culmination.
    
    I was able to follow the station until it entered the shadow where it 
    disappeared, slowly decreasing in brightness, as expected.
    
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