My friend and I were on our way to my summer place in Canada and had pulled off I-81 for a rest stop. We were looking at how beautiful the stars were and as we both gazed upward, a large cigar shaped "sillouette" floated past us very slowly. It almost appeared to be a craft silently cruising without it's lights on. It was a black shaped that moved across the horizon. It lasted approx. 30-45 seconds, then it was out of view in the dark.I estimate by it's proximety to the ground, and to us, as well as it's scale against the various buildings around that it was aprrox. 300-400 feet long and approx three times the "height" of a large airliner.