My brother in law and I were coming home from work. The time was about 7:15 pm and had already become dark. He was driving and I was in the passenger side of his truck. We were about 30 miles south of Atlanta on State Hwy 85 headed south to Senoia,Ga. We had crossed the Fayette county line and was going up this hill, which is about a one mile incline. About half way up the hill an object passed over us. It was headed east to west at treetop height. I asked my brother in law if he just saw what I did. He had. I could not discern the structual features. It appeared to be something like a light bar with three green lights. The middle light was off centered to the left but on line with the other two. The lights appeared to be about the size of a stop sign and were not flashing or strobing. The tree line obstructed my view for a few seconds then I could see it again. It was in a valley still at treetop height and moving westward. It seemed to be just gliding along. The three lights were still visible but had changed color to white This was not an airplane. I have lived around the Atl airport most of my life and have seen many aircraft at night. I also was an air traffic controller for 12 years. Three of those years were in vfr tower. The rest were at radar facilities. I've never seen what I saw a few weeks ago.