maybe a shadow of an invisible UFO. maybe there can disguise like the sky, but still there will be shadow for itits almost 4years, but i still can remember it, it happens when i having my recess time at class, and when i go out and look to the canteen's roof from the balcony, i saw a still big oval shadow on top of the roof, i turn up and see the sky, nothing was up there, it's a clear sky that day. i watch it for a moments and went back to class to ask my friend to see it, but when i'm back, no more shadows on the roof.i dont know whether it's an UFO or not, but that's my encounter. just wanna to share about it with someone((NUFORC Note: Date is approximate. We have assigned an arbitrary date in Jund 1999. PD))