I've seen zillions of these. I get emailed dozens of these shots a week. Some think they've imaged a ghost, others a UFO, or in your case Saturn. Saturn is hundreds of times fainter and smaller than your flare. It would just be a dim point of light low (about 12 degrees up) in the southeastern sky at midnight (mid latitudes northern hemisphere). If taken through a window the flare may be created by reflections between the window and the lens, not just in the lens. In any case it is due to the street light.
A street light flares because it isn't a star! The street light is many thousands of times brighter than any star. In the time exposure needed for dim stars, bright lights bounce around in a lens with many surfaces like camera lenses. Hard to take a shot of stars with a street light in it without creating a lens flare. In fact it is nearly impossible. Easy to test. Go back frame the picture the same and it will return. Since you can't duplicate things exactly it will move.
Also note there are several flares from the street light below the bright one as well. Too bad you didn't take a second shot. That would have shown it clearly to be a flare. Also you didn't see it when looking at the sky, only in the camera yet it is far brighter than the stars you did see.
Originally Posted by Flukephotog
Best answer I've gotten so far... But are you sure? Why would it affect only one star in the sky, and how would it give it rings?