We were on top of a parking garage facing due north trying to see if the northern lights would be visible on the horizon (They wernt). About 10 min after we got there (between 10 and 1030 pm) we (both my girlfriend and I, the only ones there) saw a flying object that made absolutely no noise and didn't have any lights on it whatsoever. We were about 1 mile from Pittsburgh International Airport, so there were a few planes in various places in the sky, and it was definitely not one of those. Compared to those planes, it was relatively low, as if it has just taken off (was moving away from the airport) so one would think if it were a standard plane, there would be noise from the engines or air rushing past it or whatever... But it was completely silent. Not only that, but it was completely dark too, there was not a single light on it. The only reason we saw it was because the sky had some light cloud cover, and it almost seemed to reflect some of the grounds light off of it, but it more so had a small cloud of light around it (very very very dim light, but enough to contrast against the night sky). I keep saying plane like because it kind of had that shape, but the most I could make out was a vague triangle. It moved very fast, with the entire sighting listing maybe 3-4 seconds. I first saw it about 40 degrees above the horizon, and a little more nnw than nw. It seemed to fly straight, while going away from us, disappearing into the darkness maybe 60 degrees above horizon at pretty much due NE. Being close to the airport, I doubt it was aliens or anything like that, but it was a flying object that we could not identify, which is a ufo right? There is a military base at the airport, but this was nothing like any kind of military plane I've ever seen.