Misidentification
Skeptics, debunkers, and people who are familiar with unusual natural phenomenon may propose that most (if not all) sightings of UFOs are simply misidentification.
Potential reasons for misidentification:
St Elmo's Fire
Sundogs
Ball, Bead, or Ribbon Lightning
Red Sprites, Blue Jets, or Elves
Birds or other animals
Swamp Gas
Other Aircraft
Camera and glare or lens effects
Reflections
Planets, the moon, and stars (including twinkling stars and planets)
Satellites, rockets, and the International Space Station
Lighthouses
Lamps and other man-made lights
Clouds
Temperature/Weather Inversion
Weather
Unmanned drones and aerial vehicles
Foxfire bioluminescent fungus
Fires
Fire tornados
Balloon (NASA's, helium, weather, birthday)
Meteorites
Mirages
Optical illusions
Misidentified structures (like construction cranes)
Ribbon or bead lightning
Chinese lanterns or kites
Insects
Lasers
Visual cortex issues
Flares or Iridium Flares
Steam
Heat waves
Mirages
Falling space debris or satellites
Smears or dust
Seizures
Bats
Skeptic and Debunker sites:
See also: Human/Future Human Hypothesis and Hoaxes