I had the day off and was in the bathroom. I live right against the Hudson River and in the flight path for Military Stewart Air Force Base. I hear C5's all the time low and loud but this day I heard a plane that sounded like a VERY loud reverse thrust. It was so loud I looked out the window and saw a passenger Jet barely over the tree tops. My house being on a hill, I was looking straight into passenger windows and could tell you the color of people's shirts. About 15 minutes later my wife told me a plane hit the twin towers which I figured was a Cessna or something and no big deal. It was later I realized the plane I saw one of the planes that was flying using the Hudson River as a guide to the towers that day.