Doc has the info on my close encounter – it was a Minuteman III missile launch from Vandenberg airbase. The bowl-shaped scattering patterns came from the first and second stage separations, I suppose. Greetings from the heart of the military-industrial-entertainment complex!
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We just saw the weirdest thing in the dusk sky above San Jose. Initially, it looked like a very brightly lit jet, with a thick vapour trail behind it. It seemed pretty high, but was far brighter than it should be that altitude. I thought perhaps the setting sun was catching a plane-wing at an angle. Then as we watched, a bowl-shaped vapour plume formed around the dot and behind it (a bit like the vapour blanket you can see forming around the plane halfway down this page, but I guess larger given the apparent distance). The dot carried on for a bit longer, then formed another bowl-shaped cloud. That bowl then appeared to contract in on itself, there was what looked like a scattering of debris from the dot, and the dot disappeared. The whole thing was over in less than a minute.
It was a pretty big deal – the vapour trailed crossed a sixth of the sky or more, about 40° from the western horizon. I’m sure we weren’t the only people to see it. I always wonder where to look for discussions of these geographically constrained phenomena online. Guess I’ll keep an eye on the local papers for a while.