Black Silent Hovering Triangle UFO

My boyfriend and I walked down to the lake near midnight in mid summer in 1990. We were enjoying the view in the dark when we looked up to see a giant black triangular UFO hovering above us, it looked like it was just above the height of the trees. It made no noise. We speculated about what we were seeing. It seemed to have greenish light on the edges. We marveled at how it could stay up there and made no noise. Suddenly it seemed to go forward and disappear at the same time, it seemed like it was surrounded by a cloud, or went into the cloud. We have never forgotten it, and we felt very uneasy afterward for a long time. I see now many people have reported similar sightings world wide for decades.