The disked hovered for over an hour then moved slowly and rapidly accelerated.

I was 11 or so years of age when I observed this event.My mother worked for TWA, and we lived just a few miles from SFO. I visited the airport alot,flew alot and had real interest in aviation for a kid of that age. I was attending a school student crossing guard year end picnic at Washington Park when I observed a dime sized silver object hovering in the sky approx NW of my position. It hovered for over an hour at what appeared to be the same position, making no sound I could hear. I pointed this out to a friend who also observed this. I confess that we both had read books about UFO's. Then whatever it was, began to slowly move across the sky and then accelerated at what appeared to be an extreme high rate of speed leaving a contrail that did not disipate as quickly as the departing airliners at SFO. Defied aviation as knew it.
Date is approximate.  PD