Fast, bright and low flying UFO seen over Hayward, CA.I was looking in the clear dark sky when I suddenly and accidentely saw an object which I can not explain.The object was shining bright in a white color and it moved westbound towards the Bay of San Francisco. The object was flying very fast. Much faster than any plane at this altitude and it didn't make any sound at all. I guess the object was about 500 hundred feet above ground level. Although I saw it just for about 2 sec. I can tell for sure that I have never seen such a thing before in my life. I am absolutely sure that it was not a airplane, altough there is much air traffic in this area. The object had a similar shape like a comet when entering the atmosphere, but it flew too low and it was too big to be considered as a comet.