Page "Unidentified flying object" Paragraph 5

Studies have established that the majority of UFO observations are misidentified conventional objects or natural phenomena — most commonly aircraft, balloons, noctilucent clouds, nacreous clouds, or astronomical objects such as meteors or bright planets with a small percentage even being hoaxes.

After excluding incorrect reports, however, most investigators have acknowledged that between 5 % and 20 % of reported sightings remain unexplained, and therefore can be classified as unidentified in the strictest sense.

Many reports have been made by such trained observers as pilots, police, and the military ; some have involved simultaneous radar tracking and visual accounts.

Proponents of the extraterrestrial hypothesis suggest that these unexplained reports are of alien spacecraft, though various other hypotheses have been proposed.