(David Pratt) 1. Introduction
Any light or object that is seen in the atmosphere and is not immediately identifiable is by definition an unidentified flying object, or UFO — which does not necessarily mean an extraterrestrial spacecraft. There have been hundreds of thousands of UFO sightings all over the world during the past 50 years. It is generally agreed that up to 90% of all sightings can be attributed to misidentification of familiar phenomena.













