2 neighbors, myself and my younger brother were aware that Skylab (an orbiting space-station whose orbit was decaying) was going to burn up in our atmosphere on July 11, 1979 and since we knew the day and approximate time, we decided to climb up on the roof of my parents house in Northglenn, CO and see what we could see. I would've just turned 15 in April of that year by the way. The 4 of us hadn't been up there for more than 5 minutes in an Eastern direction when one of my neighbors said "Look!" I looked behind us and saw an illuminated, silent disc about the size of a small plate, gliding over several of our neighbors homes and within 100 feet of passing over us. I've always felt, even after 36 years that the disc "sensed" that we were looking at it and when we did, it suddenly changed direction. It didn't turn or bank. It just went in the opposite direction away from us. Like a person might raise their arm up...and then down. That gentle. The disc never made a sound and glided away in a nice and slow manner just like it did as it came towards us. It was lightly illuminated so we could see its outline. No sound, no rotors, no engines. Nothing. One of my neighbors mentioned out loud "I wonder if that was Skylab?" Kind of amusing as I think about it now. I can say that it changed my life forever and I've had other incidents since then.