Possible UFO sighting in Corona, CA. Silvery reflective object flying at altitude suddenly stops and hovers.I stepped outside my home in Corona CA to have a cigarette and I looked up into the sky. It was clear with no clouds. A silver grey object was moving across the sky reflecting the suns as it traveled. It appeared small so I assumed it was either a jet or helicopter, and appeared to be at a high altitude. We get a fair amount of commercial and military air traffic so at first I didn't think much of it. The thing that kept my interest was its odd shape, which was somewhat boomerang shaped and the total lack of sound. Then it slowed down smoothly and rapidly and stopped in one place and hovered. I observed it for a few minutes trying to determine what the heck it was. I pointed it out to my sister who was also outside. I knew right away this was out of the ordinary. I ran inside my house to get my camera, and by the time I returned, it was gone. I was gone for at best 20 seconds.I scanned the sky and there wasn't a sign of it. If it had been a helicopter or jet, it would still have been in visual range. This is the damnedest thing I have ever witnessed. I know aircraft, and what is and is not possible, and I have no explanation for what could do this.