Here is my sky material. I've used the "N" (Normal) node to make the bottom half transparent. This is going to be important in getting the edge of the surf to show up using a little trick in how the refraction node works.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)