STEVE INSKEEP, HOST:
Good morning. I'm Steve Inskeep with an explanation for UFO sightings in the 1950s. The CIA released a document this year which it calls its most-read document of 2014. It reports on flights by U-2 spy planes. The document says those secret planes flying higher than anyone thought possible were mistaken for alien spaceships. Normally, a conspiracy theory would say the CIA is behind some mysterious activity. In this case, the CIA really was. It's MORNING EDITION. Transcript provided by NPR, Copyright NPR.