Star-like light flashes different colors, hovers, and moves horizontally over 20 minute period.

My mother was going to bed when something drew her attention to the window. She looked out and across from our house, above the treeline she noticed something strange so she called out to me to have a look.
I had a friend over and we both looked out the window as she pointed out a stationary light above the trees on the mountain across from our house.  To me it just looked like a star, perhaps just a little bigger or brighter than an average star, but just a star.
She told us that the light had been moving and it had flashed different colors. I think she said it had changed to red and blue.  But it was just a normal white star color and stationary when my friend and I saw it.
We went out onto our porch to get a better look, but it still just looked like a normal star and it wasn't moving.  Further, there was no sound. Well, that's not true.  There was the normal sound of a clear, windless summer night in south-eastern Kentucky: a million frogs and insects, but that was a prime indicator of normalcy. If there actually was silence, it was time to get scared.
Just as we we about to go back to whatever we were doing previously, the "star" started slowly moving to the left and my mom gave me that "told you so" look.
I can't tell you how far it moved, since I don't really know how far away it was, but as a guess, if the object was directly over the trees across from us, at least 100 feet.  Then it just stopped again.
When it moved, it moved slowly, silently and perfectly horizontally without any vertical motion.  There was no inertia to its motion when it started moving or when it stopped.
At this point I distinctly got the feeling we were being watched and I suggested we go back inside (a fact my mom brought up every time she recounted the story over following decades).
From inside the house, we watched the light for a few more minutes and then it slowly descended out of sight (or flew directly away from our house which I think would have looked the same).
I never saw any other colors of light than white, but I believe my mom did. I don't think that the object I saw would have ever caught her attention otherwise as she always had sheer curtains over her windows.
Witness indicates that the date of the sighting is approximate.  PD