Huge Triangular Craft

In August of 1987 I was walking my dogs down a service road that runs parallel highway 59 near Collinsville Alabama. The service road runs along the base of a ridgeline that extends west of Lookout Mtn.   The Triangular craft appeared from the east coming over the ridgeline. It blocked out the entire night sky (clear night) above my head and I would guess was flying at somewhere between 700-1000 ft. It had 3 lights, one at each corner in Green, Red and White.  It made no sound, basically hovering above the ridge for at least 3-5 minutes. It then banked slightly, turned due west and slowly made its way towards Hunstville. I watched it for at 10 minutes.
I didn't know what to think, it was too weird to deal with locally so I kept it to myself.
I did note that the direction it went off in houses the Military's Redstone Arsenal.