The best of the UFO 'evidence'

Strange objects filmed in Denver have again sparked debate about whether apparent UFO sightings are aliens visiting Earth or something far more mundane.

An aviation expert said the mystery objects in Denver were not an airplane, helicopter or birds.

But he said they may have been caused by debris swept into the sky.

From glowing cigar-shaped objects to tiny specks of light, we've collected some of the best evidence enthusiasts have found in recent years for extraterrestrial visitors.