I went to the window to smoke and observe a light in the sky; I was facing East.First I thought it was the moon because it was a clear night and the light was a circle on the sky.I open the window, light a cigarette and take a smoke. When I wanted to get the smoke out I put my head oustide the window an realize that the moon was on my right side; on South side. It was fullmoon that night.I looked again in front of me, and the other light was still there on the same position, not moving.I observe this phenomenon for about a few minutes, aproximately 5 minutes. The light was just there, very intense because it seems to be very far away, probably more than 5 miles. It was discribing a perfect circle on the nigth sky, not moving, on the top of the mountains.I sweetch looking at the strange light and the moon a few times, just to be sure of what I was looking.Then, in a blinking of an eye, it just desapear.