I don't know what forum this belongs in. Move it at will. I have already posted this on the APOD discussion site. Today on the way home from work, I saw a pair of sun dogs. At first I could only see the left one which was in a location where there were some wispy clouds. On the right, I could not see anything except a brightness that was more wishful thinking than sun dog. However, there were no clouds where that sun dog would be. Within 5 minutes, some wispy clouds appeared there and so did the sun dog. I assume therefore that you can't see the sun dog without the background cloud. Is this correct?