White light moving across sky expels plume.

White circular light moving in what seemed to be a fog on a clear night. It moved across the sky staying as a white circle for a few minutes. It appeared to stop, change shapes, get brighter, then a plume expelled from it. Before the plume happened you could see a perfect circle in the center, inside another circle. There is a moment before the plume that the white light reforms as a triangle inside the circle. Then it started to head away from us and became dimmer.