The days are shortening and winter is coming soon. What a better way to get pumped for the upcoming diamond dust season than reading Walt Tape's 119 page treatment on spatial halos. New effects like superparhelic circle await for their discoverers. About half of the contents is the old stuff that you may have read already, but Walt has made some changes, so it is not bad idea to go through those parts as well.
Click on the image to go Walt's page to download it.