Formation of Green Lights (high up) over Livonia, MI. USA

Another person & myself were watching the night sky, looking straight up.  We both saw what looked like a cluster of greenish lights, at a high altitude - they were in a slow, steady moving formation like a "V" - as if it were a formation of birds each carrying a green light.  The formation seemed to contain 8-10 lights, & was not in a fixed & perfect "V" shape.  We observed them moving in a southwest direction, then turned slightly, then disappeared.  Our observation lasted maybe 10 seconds, which was long enough to determine this was something unlike anything we could explain.  There was no sound - just little light green lights.  It was no airplane.  The sky was clear, & we had an unobstructed view.
Witness indicates that the date of the incident is approximate.  PD