white light

I was out walking our dogs one night, when I saw what looked like an enormous star on the horizon.This was about three quarters of a mile away from where I was standing. The star seemed to be right at the top of a heavily wooded hill, just over the tops of the trees. I looked at it for a short time and took our dogs back into the house. I don't know why, but I went back outside to see it again. I realized it was'nt a star because it was moving very slowly down the hill ,without makeing any sound. It was a white circle of light, that glided just over the tops of the trees and did not illuminate anything. All I can think of to describe the light, is that it was "self contained"?The light seemed to have hard edges. The woods should have been lit up with light but it was'nt. Then I noticed a soft blue light on the left side of the light. It did'nt flare out, but was "contained" too. It seemed to be coming from the back of the light. It(the blue light) seemed to have kind of a marbleing effect to it.After a few seconds the "blue" was'nt there anymore.. It continued on down the hill towards me and I started to get a little "rattled". It came to a complete stop about 250 feet away from me and was absolutely motionless. There was a large tree just to the front of the light, but the light did'nt shine through the branches. Then I became confused because the light just was'nt there anymore.At that point the light was roughly 30 feet in diameter. I thought it was gone. Then I noticed some kind of movement and I ran to the opposite side of the back porch. I heard a low pitched ,deep humming sound like a generator. It was sporadic like an engine thats idleing. I could make out what looked like several amber colored squares of very soft light, butcould'nt see the shape of the object they were coming from. At that point it was about 150 feet away from me. I could have easily run along side of whatever it was,it was moveing so slowly. I did'nt have the courage....I watched it for a short time and then it was gone. It ! did'nt f ly off..it was just gone. I did report it to the Pennsylvania Mufon Director.
Date is approximate.  PD