1. Marin B

    Marin B Active Member

    I saw the ISS last Thursday evening when it flew over the San Francisco area - it was a pretty impressive fly-over. Both my husband and I observed it make a couple of zig-zag movements - or at least that's how it appeared. I was wondering what would cause this and found this explanation:

    But in my case, both my husband and I saw the zig-zag motions at the same times, or so it seemed. Also, I've never noticed this before with other satellites. So is it just a coincidence - and both our eyes weren't tracking smoothly at the same times, or is there a better explanation?
  2. Mick West

    Mick West Administrator Staff Member

    Just guessing here, but perhaps you both shifted your positions at about the same time. If you are standing next to each other, and you are looking up-up-up as it goes overhead, you have to adjust at some point, and one person adjusting can trigger the other person to do so.

    I watched the same flyover from near Sacramento. I did not notice any zig-zag, and I never have.
  3. Marin B

    Marin B Active Member

    That makes sense. It was directly overhead and moving quickly, so it's likely that we were re-adjusting our gazes at the same times. I guess it's yet another example of appearances being deceiving.
  4. Dan Ly

    Dan Ly New Member

    Hi all! I know this thread is old but I found a video that I thought everyone would enjoy. Back in March, a couple of people on Youtube decided to watch the ISS transit across the Moon. They made their observations a little over 1 km apart and found a noticeable parallax. The video below shows the results from Astronomy Live's channel:

    Source: https://www.youtube.com/watch?v=80y2LP1bWH4

    Combining the baseline, parallax, and altitude he determines that the ISS must be ~408 km above the flat-Earth. A value of 414 km is found when including the Earth's curvature. Astronomy Live also determined that the ISS is about 109 m in width and has a velocity around 7 km/s. This is great independent confirmation of the space station's orbit!
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  5. Dan Ly

    Dan Ly New Member

    There is one potential confounding factor to this type of measurement. In astronomy most objects are so far away that we can treat them as positioned in an 'infinite background' from which we can measure the parallax of another object. So, in the video, it is assumed that the Moon is sufficiently far enough away for this to work. It might be interesting to run some numbers on this but I don't anticipate that the error would be large enough to have much of an effect. We do have good reason to believe that the Moon is quite far away contra the typical value of ~3000 miles given by flat Earthers.
  6. Neil Obstat

    Neil Obstat Member

    It's interesting to see an amateur actually doing the computations. I know a lot of them do this, but how many bother to make a video of what they did? It's revealing when no flat-earther has any way of showing their method of coming up with that "3,000 miles" altitude but at least they're honest enough to say that's just their opinion, or it's what they feel is a good number - it's all about feelings, you see.
  7. Dan Ly

    Dan Ly New Member

    Another example of calculating the altitude and speed of the ISS this time using a solar transit.
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  8. Astro

    Astro Active Member

    Red and I have tentative plans to run it again using the stars themselves as a background. Not as simple to do for obvious reasons, but it is possible with astrometry and a couple of computerized telescopes to point the optics at the same coordinates from two locations spaced by a kilometer or so apart. My thought is to look for transits of a readily identifiable open cluster like the Pleiades to make the task easier.
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  9. Dan Ly

    Dan Ly New Member

    Sounds good! I look forward to the results. Another interesting experiment would be to measure the Moon's parallax against the background stars. It would take more effort because you would need observers separated by several hundred miles at least but it would be cool to see how close you can get to the accepted lunar distance.