Circular object, slow moving, disappeared, silvery contrail appeared as if the object wanted to be seen

While at a drive in theater, north of Sacramrnto, CA and within 2 miles of McClellan AFB, 3 members of my family and myself saw a very large disc shaped object flying from north to south over the large, outdoor, screen just as the film started, about dusk.  
The size of the object was approximately 80 to 90 feet in diameter.  It was silvery in appearance, without any markings and did not display any join lines or riveting, as do conventional aircraft skins.  It appeared to have a fluted exhaust at the rear, with a long silvery contrail egressing from it. What appeared to be windows around the upper edge of the disc were all lighted.  
It was moving far slower than any aircraft should have been and was not "spinning." It also was not making any noise at all.  The attitude of the craft was such that it appeared that it wanted to be seen, and seen it was because every car in that drive in was emptied and the occupants were standing, staring at the sight of it.  
As suddenly as it had appeared, the contrail blinked completely out and all the windows darkened. It was visible for only seconds after that and quicker than the mind can imagine, it was gone. It didn't appear to speed away, it just vanished.