I witnessed a disk-shaped craft, with colored lights, move very slowly towards the northwest, in Clark County, Kentucky.

This event transpired about 30 years ago and I am unsure of the exact date.  It was probably early spring or late autumn of 1976, but I could be off by a year either way.  The temperature was in the low 50's and the leaves were off the trees, which is why I believe the season was early spring or late fall.
 My sister had been out at a bowling alley with a friend of hers, and her friend's mother.  In the early evening, but well after sunset, she returned home, and burst in through the front door in a state of excitement.  She announced that they had been followed by a UFO while driving to our home (which at that time was a couple of miles out in the country).  I said, "gee, I wish I'd seen it", to which she replied, "well, you probably still can.  Go look out my window!"  I ran to her bedroom, and looked out the window, which faced the northwest...and I could clearly see the disk.  It was about 65 to 70 feet in diameter, and perhaps 5 to 6 feet thick.  It hovered about 150 feet up.  It was moving very slowly, perhaps only 4 mph, roughly toward the northwest.  The disk had lights on its edge; I saw red, green, blue, and white.  They lit up in sequence, moving from right to left along the edge of the craft.  Because of the timing of the lights, I gained the impression that the lights would have been present all around the disk, but I only saw the edge that was facing me.  Each light would blink on for about a 1/2 second, then off, and its neighbor to the left would blink on, etc.  The night was clear and my view of the craft was quite sharp, but I did not perceive any other features of the craft besides the lights. At no time did I hear any sound from the craft.
 The disk continued to recede away from me, toward the northwest.  I watched it for perhaps 5 minutes, and then I left the room.
 I have had an acute interest in military aircraft since early childhood, and I know enough about aircraft to realize that this was not an airplane or a jet, and it certainly wasn't a weather balloon.  It was travelling at a rate far below the stall speed of any normal aircraft, hardly greater than the normal walking pace of a human.
Witness indicates that the date of the incident is approximate.  PD