Saturday, May 3, 2008
The most generic definition of an Unidentified Flying Object, or UFO, is any flying object or phenomenon that cannot be identified by the observer. Various studies show that after investigation, the majority of UFOs are usually identified, and are relabeled IFOs or Identified Flying Objects. Therefore, some stricter definitions reserve the label "UFO" for only those instances where the objects remain unexplained after a proper investigation. The percentages of IFOs vs. UFOs varies with the researchers, study, and case sample, ranging from only 5% to 10% being UFOs, according to The J. Allen Hynek Center for UFO Studies,  to 20% to 30% being UFOs according to earlier U.S. Air Force statistics or the later Condon Committee.
UFOs have been spotted in many different places around the world. Reports of unusual aerial phenomena date back to ancient times, but modern reports and first official investigations began during World War II with sightings of so-called foo fighters by Allied airplane crews and in 1946 with widespread sightings of European "ghost rockets." UFO reports became even more common after the first widely publicized United States UFO sighting, by private pilot Kenneth Arnold in the summer of 1947. Many tens of thousands of UFO reports have since been made worldwide. 
Unusual aerial phenomena have been reported throughout history. Some of these phenomena were undoubtedly astronomical in nature: comets, bright meteors, one or more of the five planets which can be seen with the naked eye, planetary conjunctions, or atmospheric optical phenomena such as parhelia and lenticular clouds. An example is the Comet Halley, which was recorded first by Chinese astronomers in 240 B.C. and possibly as early as 467 B.C.
Other historical reports seem to defy prosaic explanation, but assessing such accounts is difficult, because the information in a historical document may be insufficient, inaccurate, or embellished enough to make an informed evaluation difficult.
For example, in the Old Testament of the Bible, Ezekiel apparently had a first-hand encounter with something that might now be described as an Unidentified Flying Object, but which the Bible describes as a fiery chariot.
Whatever their actual cause, such sightings throughout history were often treated as supernatural portents, angels, or other religious omens. Art historian Daniela Giordano cites many Medieval-era paintings,
frescoes, tapestries and other items that depict unusual aerial objects; she acknowledges many of these paintings are difficult to interpret, but cites some that depict airborne saucers and domed-saucer shapes that are often strikingly similar to UFO reports from later centuries. (See List of UFO sightings)
Shen Kuo (1031–1095), a Song Chinese government scholar-official and prolific polymathic inventor and scholar, wrote a vivid passage in his Dream Pool Essays (1088) about an unidentified flying object. He recorded the testimony of eyewitnesses in 11th century Anhui and Jiangsu (especially in the city of Yangzhou), who stated that a flying object with opening doors would emit a blinding light from its interior (from an object shaped like a pearl) that would cast shadows from trees for ten miles in radius, and was able to take off at tremendous speeds.
Kenneth Arnold's sighting and the 1947 U.S. UFO wave
The post World War II UFO phase in the United States began with a reported sighting by American businessman Kenneth Arnold on June 24, 1947 while flying his private plane near Mount Rainier, Washington. He reported seeing nine brilliantly bright objects flying across the face of Rainier towards nearby Mount Adams at “an incredible speed”, which he "calculated" as at least 1200 miles per hour by timing their travel between Rainier and Adams.
His sighting subsequently received significant media and public attention. Arnold would later say they “flew like a saucer would if you skipped it across the water” (it would ricochet) and also said they were “flat like a pie pan”, “shaped like saucers,” and “half-moon shaped, oval in front and convex in the rear. ...they looked like a big flat disk.” (One, however, he would describe later as being almost crescent-shaped.) Arnold’s reported descriptions caught the media’s and the public’s fancy and gave rise to the terms flying saucer and flying disk. Arnold’s sighting was followed in the next few weeks by hundreds of other reported sightings, mostly in the U.S., but in other countries as well.
Another case was a United Airlines crew sighting of nine more disc-like objects over Idaho on the evening of July 4. At the time, this sighting was even more widely reported than Arnold’s and lent considerable credence to Arnold’s report. In fact, American UFO researcher Ted Bloecher, in his comprehensive review of newspaper reports, found a sudden surge upwards in sightings on July 4, peaking on July 6-8. Bloecher noted that for the next few days most American newspapers were filled with front-page stories of the new “flying saucers” or “flying discs.” Starting with official debunkery that began the night of July 8 with the Roswell UFO incident, reports rapidly tapered off, ending the first big U.S. UFO wave.
Over several years in the 1960s, Bloecher (aided by physicist James E. McDonald) discovered 853 flying disc sightings that year from 140 newspapers from Canada, Washington D.C, and every U.S. state save Montana.