Scintillation

Scintillation is the atmospheric twinkling effect that makes stars appear to flicker, and low, bright stars in particular appear to shift rapidly through red, green, and blue hues, caused by turbulent pockets of air at different temperatures and densities bending starlight unevenly as it passes down through the atmosphere before reaching an observer's eye. The effect is dramatically stronger for stars low on the horizon, where light must travel through a much longer and more turbulent path of atmosphere than light from a star directly overhead, which is exactly why bright, low-altitude stars like Sirius and Capella generate a disproportionate share of "color-changing UFO" reports and videos, particularly ones filmed on smartphone cameras whose sensors exaggerate the color shifts even further than the naked eye perceives them. Investigators reviewing this report category typically check three things: whether the reported object's position matches a known bright star or planet's actual sky position and time, whether the "movement" described is consistent with autokinesis rather than genuine travel across the sky, and whether the footage shows the light holding a fixed compass bearing over hours — the signature of a genuine celestial object rather than a craft. Scintillation and autokinesis together explain a substantial share of long-duration, apparently erratic UFO video submissions.