Sky's the limit, Part II

I get a lot of sympathy pats because people assume it must really SUCK to live in a brand new neighborhood that does not yet have mature trees. 

While I'd prefer the trees, the prairie scene has its benefits.  First, the breeze is almost always blowing across the fetch, making it feel significantly cooler and suppressing mosquitos, thus making midsummer evening walks downright pleasant (say THAT about a 30-year-old subdivision).  Second, I've never in my life spent so much time looking at the sky, because now I CAN - there's an actual full dome above us with a distant horizon - and I see things that are lost to people who are wooded in. 

Case in point tonight, this radiating pattern from the southeastern horizon 180 degrees from where the sun was setting - in other words, exactly at the point where sun will rise tomorrow morning.  This happened during an otherwise-unremarkable sunset, and neither of us can figure out why (one aerospace engineer and one scientist with some astronomy background thusly strike out).  Even if the sunlight were refracting around the atmosphere, I still don't see why it would appear to converge like that at the horizon.  The streaks appeared to extend across exactly half of the dome - that probably has something to do with the explanation.

I'll leave some thinking space here in case someone writes me and says, "Oh yeah, that's caused by _______________________________________________________________"