two swept wing objects, in erratic formation, flying very, very fast at night, lit up very strangelyOn May 10th at around 2230 my wife and I together saw what we would describe as two UFOs. Neither of us has ever seen anything like this, and we both agreed on what we saw.We were at the Shoreline Amphitheater in Mountain View, CA. We were lying on the lawn, at a concert. There were various ordinary looking airplanes in the air, all lit up normally.Suddenly, we saw two small swept wing shapes quite high up, in formation, but the trailing object was in very loose, and erratic formation with the leader. This was unlike any kind of normal military jet formation I've ever seen. ( I am an ex airline pilot.) The two were on an westerly heading, flying very, very fast, faster than any military jets would fly, and they were lit up on their undersides in a kind of feathery light, but the entire underside was lit up. We could not see any detail, except that they were small, swept wing objects. They made no sound at all.As I have said, my wife and I both saw the objects, and we did not disagree on what we had seen. It was the first time in either of our lives that we realized we had seen something that did not look human-related. We would very much like to know what we were seeing.