Bright light zig-zagging through sky.While camping in Michigan's western upper peninsula, approximately 10:00 p.m., CST, I was watching for Perseid meteors. I suddenly noticed a very bright light which I estimated to be in the -2 to -4 magnitude range, traveling in a SSW to NE direction through the constellation Ophiuchus. It moved in a zig-zagging, back and forth manner, at very high speed. At least 2 to 3 times the speed of satellites I had observed, and about 1/2 the speed of a meteor. Within 3 to 5 seconds, the object disappeared behind the trees. Altitude: Very high. Earth orbit, or near earth orbit. Size: Apparently very large. Possible dark or hollow center. Couldn't tell for sure. Also on the same night, I saw at least three bright flashes of light in differant locations, at differant times. These were very brief, lasting only 1/2 to 1 second each time.