Other forms: unidentified aerial phenomena
An unidentified aerial phenomenon is an object in the sky that can't be explained. That flashing light moving overhead might be a satellite or an alien spaceship — but it's definitely an unidentified aerial phenomenon to you.
Another name for these unexplained space objects is unidentified flying object or UFO. Recently, NASA officials began using the more scientific-sounding unidentified aerial phenomenon instead. Then they changed it to unidentified anomalous phenomenon to include all unidentified objects, including on land or sea. But if you spot anything strange and mysterious in the night sky, you can call it an unidentified aerial phenomenon. Aerial means "in the air" and phenomenon means "observable fact."