Re: ISS observation / question

From: Tom Wagner (
Date: Sun Jan 28 2007 - 14:06:53 EST

  • Next message: Wally Anglesea: "RE: ISS observation / question"

    Paul Floyd asked:
    Is it possible using binoculars to seeing the station as an very slightly 
    elongated shape? The binoculars are labeled 'Gerber Sport', 10 by 50 with 
    288 ft at 1000 yds.
    Hi Paul,
    One of the "satellite lessons" that I developed recently touches on this 
    exact question. The lesson has the kids place an image of the ISS at a 
    distance that puts it into a true perspective so that they can look at it 
    through binoculars and through a telescope to see what they can expect to 
    see under "perfect" circumstances.
    Now I hope my math is correct here. :~) The angular size of the ISS at a 
    particular distance should be a simple matter of working with ratios. E.g., 
    if you have an image of the ISS to look at that is 100 times smaller than 
    real life, to view it the way it would be seen in a real life situation, 
    place it 100 times closer than what it was at the time you saw it. This 
    assumes (1) that you know the distance that the was at the time of 
    observation and (2) you have a picture that matches its orientation. I use a 
    good image of it and use its average distance above sea level as a start.
    What I have the students do is this: Print a picture of the ISS, like this 
    I made then measure the mms across one of the main 70 m solar arrays. From 
    this they determine the scale of the image and multiply that times the 
    distance to the station. I use the average distance, which, as I recall is 
    342 km. That gives the distance in km to place that printed picture to see 
    it in the proper perspective. I convert the km viewing distance to meters 
    then measure it out. Place the ISS picture on a stick or wall and move away 
    the distance calculated then take a look with your binoculars.
    You will find that the ISS picture better be on the order of 3 cm across or 
    less. Otherwise you will be measuring a very long distance!
    And yes, using this technique and a 7X binoculars [on a tripod] one can just 
    make out the shape of the ISS. I suppose that glints would be even easier to 
    make out than the B&W paper image is. This is a hypothetical situation and 
    may lead to some misconceptions. But it's a good start.
    Tom  Iowa  USA
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