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?