large aircraft blinking red and green lights alternately

A red blob in the night sky that did not move as I watched for a couple of minutes, I left and in a short time went to another window and this time saw it was coming closer, seemed quite low, and I could hear a low rumble of sound that got louder. It was large, turned from coming my way to my right (north), and it looked nothing like an airplane or anything I had seen before. It did not move fast but when turned sideways to me it was blinking alternately all over red and green lights. The lights seemed to be all over the aircraft so it was obviously huge.