Hovering object. Summer night. Red/green blinking light. No wind. No sound from object. Slowly began to move and slowly fly away.

Hello. I just wanted to share my story with you.  This happened a long time ago.  I think it was 1985.  I was probably 17 at the time.  I am from a small town in North Dakota called Belfield.  It is in Stark County.  
One weekend night I was in a car with a friend.  His brother and my sister were in a car behind us, and there was another car with two people from our town behind them.  So, there were six people that saw this.  
We were driving out in the country somewhere south of Belfield, probably about 10pm, and we were looking for a person’s farm, who was having a party.  Outdoor parties were common for us back then.  
We were in the lead car and I saw a red and green or red and blue light blinking in the sky.  It just seemed out of place, and the lights were separate not together.  I pointed it out to my friend driving, and he saw it.  
We decided we needed to pull over and talk to the others behind us because we did not know how to find this party.  We pulled over and stopped.  Now, we were not on a highway, but on a dirt country road.  We got out and we were almost right underneath these blinking lights.  It was not very high, maybe a hundred feet, but just high enough that we could not see the shape clearly, but it seemed to be 50 ft. wide, judging by the blinking light on each side.  I could be wrong about the size.  There was no radio tower or tall pole with lights on it nearby. 
The weird thing is that it was a still summer night, no wind, and this thing was blinking above us, and we did not hear a sound.  No engine.  No propeller, etc., yet it was hovering.  
I started waving at it, and I grabbed a flashlight out of the car, and started to flash the light at it.  
After about a minute, or so, it began to slowly move kind of around us, and then continued to fly off across country to the south west at a slow rate of speed.  
I will never forget that experience and have no idea what it could have been.
Witness indicates that the date of the sighting is approximate.  PD