I was reading an article in the Pennsylvania Turfgrass Council magazine on Fairy Ring. This is a soil fungal disease that can be treated, but it takes several applications and it can be a slow recovery. Fairy ring is fairly common and can be worse in lawns where roots and stumps were buried. There are 3 types of fairy ring; in some cases it leaves a dark green circle, others it can kill grass and the final type grows a ring of mushrooms.
I once saw and interview on television where an individual thought they were caused by the exhaust of an alien spaceship. Unfortunately, that's not the case although I wish it was. At HCC, we are fortunate to rarely deal with fairy rings, although we have seen it in the past on #10 approach.