I was at the beach flying a training kite at 3:30pm, when I saw a equilateral triangular craft with three powerful white lights, one at each vertex. It was 30 degrees to the right of the sun. It was stationary, at an altitude higher than commercial jets. There was a clear blue sky. I saw it for around 12 seconds, then it vanished by apparently rising to a higher altitude. It vanished as if rising above clouds, but there were no clouds. In other words, it seemed to get higher into the stratosphere. An equilateral triangle with three bright lights at the vertices. I saw a grayish structure. I estimate the size to be around the length of 3 commercial Jets.I'm a civil engineer, aerospace and aeronautics enthusiast, astronomer and plane spotter. I've been flying remote controlled airplanes and helicopters for 25 years. I know what I saw. A 12 year old kid next to me also saw the object.