Extremely huge, very slow moving object seen in the sky by 7 witnesses.

I was babtsitting for neighbors and as they were coming in the house, the mother called out, from outside, for us to come outside to look. 
We all went outside. In the sky was a completly black bicycle horn shaped UFO.  It had a large round shape in the back with a cylinder in the middle and cone shape in front of that.  Out of the cone shaped front was shining a huge light.  
The UFO appeared to be about the size of a football field, or maybe a little bigger even.  It was moving extremely slowly and was hanging very low in the sky, much lower then normal aircraft.  We all stood there with our mouths open for easily 15 minutes watching in silence as it moved in slow increments across a very short distance. 
Suddenly the "front" light went out and maybe two or three seconds later the now completely dark shape disintegrated like ashes.  Particules just seemed to hang in the air for a few more seconds and then there was nothing.  After maybe a few seconds we all erupted with sound, confirming that we had all seen it.  What we had seen, etc.  
The father went in and called the police who, after several phone calls told him that they had some report that some air force base was conducting test flights of some craft they had.  The only air force base at the time was many many miles away and to this day I do not believe that we have the capacity to hold an object that huge in the air nor have it move that slowly with out it crashing, much less the fact that it completely disintegrated into nothing.
Witness indicates that date of incident is approximate.  PD