When I was researching heiligenschein recently, I also read about Sun dogs a.k.a. parhelia or false suns. I'd heard the term but had never seen the phenomenon, although it's apparently not rare.
OK, so if sundogs are fairly common, I should start seeing them once I started looking for them, right?
It looked much brighter in person. There are usually two, spaced evenly on either side, about 22º away and at the same altitude as the sun. I couldn't see the twin on the other side, even when I moved to a vantage point without trees. The clouds on that side looked different. Thicker.
When I first saw it, I thought it was a rainbow, or rather cloudbow. It looked like the lower arc in this picture, with the addition of a bright white spot just to the left. We were almost home from the grocery store, but by the time I rushed in to grab the camera, the long "bow" portion of the parhelic arc had vanished, and never returned. The sun dog got brighter and dimmer as the clouds shifted.
I was a happy camper.
Parhelia are formed by light passing through horizontal hexagonal plate ice crystals in the clouds. Certain types of clouds produce them more often, and they are most often seen when the sun is low. (See here.)
Another good site for atmospheric optics: