About half a dozen years ago, I was having an unauthorized smoke break at my 2nd job. About 11 pm, standing on a deck that looked out to the Missouri River. The sky was generally clear, some clouds in the distance.

About a mile out, half way across the river, and about 500 to 1000 feet vertical, I got to observe some "ring lightning".
Here's a pic off the internet that shows what is called "ring lightning"

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The ring lightning in that stock photo isn't quite what I saw.
In the stock photo, the "ring" was apparently created from two different lighting bolts. Difference in potential, path of least resistance, atmospheric conditions between the bolts, etc seemed to created dual bolts that formed a "ring" of sorts.
The edges of the "ring" are somewhat ragged in areas, somewhat smooth in others. Mini bolts can be seen coming off the ring.

The "ring lightning" I saw was different.
Visually it appeared to be a perfect circle.
No ground-to-earth bolts or cloud-to-cloud bolts. No apparent source for the ring.
The edge of the solid ring had a well defined, sawtooth effect, completely around the entire ring.
The ring appeared in its entirety, lasted approximately 10 seconds, then disappeared in its entirety.

I'm a firm believer in "What is, is and What ain't, ain't".
I mention that because I have no idea what it was that we saw. The appearance of ring lightning, to be sure.
But .... how ? And why such a perfect circle, with a well defined saw-toothed edge ?
Lightning has an extremely high temperature that rapidly heats up the atmosphere around it. Yet this ring held its shape for 10 seconds, with no distortion.
After 10 seconds, it didn't "dissipate", it just .... went out.