One night years ago, my brother and I saw large twin discs moving westward in tandem low and parallel to the ground. As they continued west, twice the discs traded places with each other in a smooth mechanical manner.
We may have observed technology, certainly the formation and movement strongly suggests this.
However, a natural phenomenon can’t be ruled out either. It could be some form of ball lightning. Science is also investigating aerial phenomena created by the dynamics of geology. Google the light shows that have been recorded during earthquakes.
But I am certain that I can rule out swamp gas, weather balloons, Venus, traditional aircraft, swimming pools, etc.