Walking down the street I noticed what looked like a faint star moving through the constelation of Orion. It looked very high up and I thought it was maybe a jet flying from west to east. Then I thought it looked more like a satalite because at that altitude jets appear to fly slower, they don't cover as much space, this was moving pretty fast, and I was thinking how rare it is to see a satalite through the light polution of the city (San Francisco). I watched the object for aboutg 5 or 6 seconds then all of the sudden it changed directions at 90 degrees, and was going to the north. After about 2 seconds it disappeared. This turn was sudden, unlike anything flying that I am familiar with. The only other explanation is that I had some object moving across the cornea of my eye, but I doubt this as it doesn't behave like "floaters" we can sometimes see in our eye. I was a bit shaken by the experience. The object was as faint as a faint star, looked more like white light than blue. There were no other colors and it was constant, not blinking or oscillating in intensity.