I've completely missed this thread...
Last winter I saw this phenomenon going home from work. It was one of those days I hadn't brought my camera with me, and the phone failed miserably in my attempts to capture it. As I got home the light was failing fast, so I ran in and grabbed the camera. It had the Carl Zeiss 50/1.7 mounted - a bit tight to get it all, but no time to change lenses.
I'm just happy I managed to get this picture
I haven't checked with anyone, but as it was cold and sunny that day I assume this is ice particles in the atmosphere acting as prisms splitting the sunlight.