Unique view of ISS passing through branches

From: Tom Wagner (sciteach@mchsi.com)
Date: Sat Jan 06 2007 - 20:29:58 EST

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    Eager to take a break from my studies, I ran outside to observe a low, 
    twilight pass of the ISS. Through 7 x 35 Pentax binoculars it looked like a 
    pale copper-colored glistening dot. Due to its low altitude it soon passed 
    behind a tree that was about 100 feet away. When it emerged from behind a 
    large branch it appeared as two distinct dots rather than one!! For several 
    seconds it drifted behind small branches and continued to look like two 
    distinct dots. I quickly realized that, as I see happening when I stereofuse 
    two images to see them in 3D, when things up front look like one fused image 
    things farther away appear as doubles, or vice versa. This doubling effect 
    is something that people that are familiar with looking at stereo images 
    should relate to.
    I found that the tree was far enough away that the depth of field was 
    sufficient to see both the tree and the ISS in almost the same focus. While 
    the ISS was passing through the branches I found that I could hardly force 
    both my eyes to align on it to see it as one dot. When I did, because of the 
    complex nature and the low contrast of the small branches, I didn't notice 
    that they were then paired. Finding it hard to fuse the ISS into one was 
    peculiar to me because when viewing stereo images I can easily manipulate 
    the angle of convergence of my eyes. Soon I realized that seeing two was 
    desirable because they appeared like the beautiful ISS/Shuttle pair many of 
    us saw recently. Quite a show, albeit a false one.
    Clear skies,
    Tom  Iowa  USA
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