Triangle shaped UFO observing thunderstormsAir temp 85 degrees, wind out of east about 10 mph. I was laying on the ground looking directly upward, and saw a triangle shaped object enter my field of view from the southeast headed toward the northwest. This object consisted of a black triangle shape, six white lights (3 along each arm of the triangle) with the "point" angle about 50 degrees. The object was much larger than a normal aircraft, and totally silent. It appeared to be at about 10,000 feet (I live near a major airport therefore know approximate heights). The lights were exactly the same size and intensity as the stars that were out that night. The object moved about halfway across my field of view in about three seconds. In one second, the object appeared to make a 90 degree vertical turn, that is, move from horizontal flight to direct vertical flight. The change from horizontal to vertical happened in about one second, and in a space of about the length of the object, i.e. much faster and more smoothly than a normal aircraft, and without sound. I remarked to my friend, who was nearby: "Hey, it's a triangle shaped UFO" and by the time he looked up, the object had vanished. However, while he was looking at the same spot a moment later, he reported a "shooting star". Notes: At the time of the sighting, a line of hellacious thunderstorms were forming directly to the northwest, the approximate direction of travel. These storms contained heavy lighning, and 70-80 mph winds. Also: We were part of a bicycle riding event, and there were several thousand campers in the area, so there may have been more sightings.