A disk shape hovering over my apartment building in broad daylight in a busy city.

This happened when I was 15 years old. My mother had taken me, my brother,my friend, and her roommate to get Kentucky Fried Chicken in her van. When we got back to the entrance of our apartment building (The Village of the Pines on 700 E. Peckham Ln.) my mother yelled, "look at that" and pulled off on the street (not entering the driveway) and we all got out and looked at this weird round thing hovering over the apartments. It seemed to me that the top 1/3 of the craft had windows and I remember trying to see if I could make out the shadows of the people(?) moving around inside. The bottom of the craft was lit up but did not seem to be bright (it was still daylight). There was a slight humming sound the whole time, then it went off over the back part of the apartment complex. It did not "zip" off, but seemed to be at a fairly regular plane speed. The strange thing is that the roommate and my brother immediately afterward claimed they didn't see a thing, even though I remember them wondering aloud as to what it might be. I have always personally thought that it might have been some kind of top secret aircraft of the US government. This apartment building is directly acrtoss a K-Mart, and is close to the airport. It was daylight on a busy street, and a few cars did stop, but I don't remember anyone else getting out.  I have never reported this sighting as it always seemed to weird. This incident did get me interested in the subject of UFO's but I have never seen a description like mine. This is the main reason why I think it may have been some kind of test craft.