While on a Delta Airlines flight from NY to Fort Lauderdale flying over the Norther Atlantic Ocean, flying at approximately 29,000 feet, Jan 2, 2017 several passengers and I observed a silver oval UFO hovering over the clouds. The UFO changed from solid to translucent. I took several photographs of the UFO with my I-phone. The UFO was at an altitude of approximately 40,000 feet. The UFO was last observed moving in an unknown direction into clouds. No other aircraft were observed at the time of the sighting. At first sight I thought the UFO Sighting was a plane and then a weather balloon, but then the UFO was observed to appear to almost disappear/invisible or become translucent in quick intervals. mufon cms# 83056