Two large, 30' diameter spheres of light appx. 30' apart, appx 20-30' overhead, seen by 60? people, passing slowly overhead silently, no vehicle shape.

My sister, her kids and I were riding in her convertible sometime in the summer of 64-66 ? on a back road (Old Federal Hill Road) when we saw two large spheres of light coming towards us.  As we approached the main road, we saw dozens of cars pulled off the main road (Rte 165 - 3 miles north of Jarrettsville) and people scrambling up the embankments to watch what we were also witnessing.  The lights looked like the headlights of a very large jetliner, but as it came closer we realized that they were too low to the ground and too big to be jetliner lights. And as it came closer and went overhead (apxy 20-30 feet above us), it had NO sound, NO shape of any craft joining the lights together.  They travelled in unison, going maybe 10-20 mph.  As they drifted silently above us, several of us reached up like we were trying to touch it, it felt that close.  The really strange thing was that after it went over, the lights were still visible (as headlights would not be going in the opposite direction).  Everyone stood quietly mesmerized until it disappeared over the Eastern horizon. When it finally disappeared everyone just sort of looked at one another and let out a nervous whispered giggle and said "What the hell was THAT!?!"  No one knew. When we got to our parents house, my mom called the local airport and also BWI -- and no one had an explanation.  She called the Air Force and they gave several "viable" explanations -- "weather balloon", "ball lightning" (yeah, right... going 10 mph over a period of half an hour!) and "swamp gas".  At this point we gave up.  I was probably 12 at the time, but it is still as vivid to me as it was 30+ years ago.