
The first event the "V", which appeared over northern Arizona and gradually traveled south over nearly the entire length of the state, eventually passing south of Tucson was the apparently "wedge-shaped" object reported by then-Governor Symington and many others. This event started at about 20:15 MST over the Prescott area, and was seen south of Tucson by about 20:45 MST.
Proponents of two separate events propose that the first event still has no provable explanation, but that some evidence exists that the lights were in fact airplanes. According to an article by reporter Janet Gonzales that appeared in the Phoenix New Times, videotape of the v shape shows the lights moving as separate entities, not as a single object; a phenomenon known as illusory contours can cause the human eye to see unconnected lines or dots as forming a single shape.
More:
http://en.wikipedia.org/wiki/Phoenix_Lights#First_event
Below: At least one photo of a reported triangle (in the Belgian Wave) was a hoax.

The mystery of the iconic Petit-Rechain black triangle UFO photo has finally been solved. The photographer, a man named only as Patrick, has admitted making the UFO out of polystyrene in an interview with mainstream Belgian TV channel RTL-TVI.
The photograph was taken 21 years ago in 1990 at the height of the Belgian UFO flap and was an instant hit around the world, with many publications using the photo as a kind of banner for the UFO phenomenon.
It was known as the Petit-Rechain photo after the Belgian town where it was photographed, but Patrick revealed he and some friends made the model in a short space of time before photographing it some hours later that evening.
More:
http://www.realityuncovered.net/blog/2011/07/famous-black-triangle-ufo-a-fake/
I think UFO sightings believed by observers to be alien craft are either hoaxes, misidentifications of known objects, or of unusual weather phenomena, such as this plasma event:
