Contour Illusion

A contour illusion is a well-documented perceptual effect in which the human brain, presented with several separate but closely spaced light sources moving together at night, automatically completes the gaps between them into a single continuous dark shape or solid body — effectively "connecting the dots" between individual lights the way the brain naturally fills in a dotted outline, even when no solid object is physically present between them. The effect explains why a tight formation of conventional aircraft flying together at night, each showing only its own navigation lights, can be honestly and sincerely reported by a truthful witness as one enormous, silent, solid craft appearing to "blot out the stars" as it passes overhead — a description that sounds implausible for aircraft but makes complete perceptual sense once the underlying illusion is understood. The 1997 Phoenix Lights case remains the illusion's most cited real-world example, since one component of that night's sightings — the earlier V-formation of lights many witnesses reported — is widely explained by investigators as several aircraft flying in tight formation, their lights perceptually merged by contour completion into the single vast triangular craft so many witnesses vividly and sincerely described seeing that night.