an excerpt of interest from Wikipedia's Unidentified flying object article...
Typical reported characteristics of UFOs
- Saucer, toy-top, or disk-shaped "craft" without visible or audible propulsion. (day and night)
- Rapidly-moving lights or lights with apparent ability to rapidly change direction — the earliest mention of their motion was given as "saucers skipping on water." Disc-shaped craft are sometimes reported to move in an irregular or "wobbly"manner at low speeds.
- Large triangular "craft" or triangular light pattern
- Cigar-shaped "craft" with lighted windows (Meteor fireballs are sometimes reported this way).
The number of different shapes, sizes, and configurations of claimed UFOs has been large, with descriptions of chevrons, equilateral triangles, spheres, domes, diamonds, shapeless black masses, eggs, and cylinders. Skeptics argue this diversity of shapes, size and configurations points to a socio-psychological explanation. Other researchers argue that the large diversity of UFO shapes points to a possible paraphysical origin. Still others argue that there is a large diversity in the shapes and sizes of human flying craft, reflecting different origins, propulsion systems, and purposes, so such diversity in UFOs is not necessarily unexpected or inexplicable.
Another argument is that the true underlying shape may, in some cases, be concealed or distorted by the ionization of air around the objects, believed by some researcher advocates, such as NASA engineers Paul Hill and James McCampbell, to be a characteristic of the propulsion system. Air ionization could also partly explain the diversity of colors reported, as different air molecules are excited at different energy levels, as well as the electric, neon-like glow around the objects often reported, similar to what happens with polar auroras. Another view is that the shape may be concealed or distorted by space-time distortions arising from an anti-gravity propulsion system. However, some feel that such speculation is overly premature because the very actuality of UFOs as alien craft is itself problematic.
Other advocates, arguing for the non-conventional interpretation, reply that the volume of impressive sightings reported by witnesses, from commercial airline pilots to United States presidents, and occasionally captured on film and radar, possesses strong consistency and cannot be explained away simply as mundane phenomena (weather balloons, aircraft, Venus, etc.).
One writer contends that UFO mass sightings--sometimes called "flaps"--are "a hard core of genuinely unusual sightings ... surrounded by a great deal more misidentification, wishful thinking and general flakiness." 
Other researchers, such as Jacques Vallee, argue that if UFO sightings are motivated by some mechanism through which the public can release hidden fears and satisfy a psychological need for fantasies, why did "UFO waves" not coincide with such science-fiction feats such as Orson Welles' radio adaptation of The War of the Worlds in 1938, or the motion-picture versions of Flash Gordon (1936-37)? Vallee points out that the theory regarding how the general public generates and propagates UFO reports as a way of releasing psychological tensions, is denied by the absence of correlation between notable periods of interest in science fiction and major peaks of UFO activity. It should also be noted that no single, comprehensive "psychological" theory to explain the generation of all UFO reports has yet been proposed. A notable attempt on the basis of his theory of archetypes was made by the Swiss psychiatrist Carl Jung in his book Flying Saucers (1959). Jung, however, also felt that at least some UFOs were "nuts and bolts" craft, based on physical evidence such as simultaneous radar contact.