Bright flash directly overhead in night sky, lasting two or three seconds.I was lying on my back in my sleeping bag in my tent looking at a very bright star almost directly overhead (Vega). As I was watching, a little to the left (I was facing south), near the constellation Hercules, it appeared that a star was growing brighter. Within about three seconds, this object became the brightest object in the sky, easily as bright as an aircraft landing light and many times brighter than any stars in view above, but with a bluish quality to it similar to the strobe lights used on communications towers. Then the light simply winked out. I made a note of the time, then watched the sky until about 22:45 before falling asleep. I also watched the sky in the area for satellites and aircraft but saw none. During the short period that the object flashed it appeared to be stationary. I tried to see if it might be a strobe from a passing aircraft, but I saw and heard none. It was also much brighter than any aircraft strobe I had seen previously. The object was astoundingly bright, even as I looked directly at it (I know how objects can appear brighter at night when caught out of the corner of your eye). The following evening, I attempted to see if it would occur again and have submitted a report for what I saw on the evening of July 31.