UFO is a misunderstanding of known phenomena or objects. The factors or objects mistaken for UFO phenomena include celestial bodies: planets, stars, meteors, comets, meteorites, etc; UFOs may be atmospheric phenomena: spherical lightning, Aurora, magic sun, magic moon, Elmo fire, mirage, earth light and floating clouds are mistaken for UFO creatures: birds, butterflies, etc; Biological factors mistaken for UFO: residual images in human eyes, eye defects, illusion of aircraft reflection in oceans and lakes, etc.
UFO may be optical factors: Photo artifacts caused by internal reflection and development defects of the camera, overlapping images caused by reflection of windows and glasses, etc; UFO may be a radar false target: radar sub wave, abnormal refraction, scattering, multiple refraction, such as reflection from electric dense layer or cloud layer or reflection from high temperature and high humidity area.
UFOs may be man-made devices: aircraft lights or reflected sunlight, man-made satellites re entering the atmosphere, rockets, balloons, military test aircraft working after ignition, searchlights reflected in clouds, flares, flares, beacon lights, parachutes, secret weapons, etc. UFOs may be the product of highly civilized extraterrestrial life: some people believe that some UFOs are aircraft made by highly civilized life (aliens) on other planets. UFO may be the aircraft of underground people: the aircraft of creatures living in the interior of the earth.