Introduction

Unidentified Flying Object (UFO), any object or light in the sky that cannot be immediately explained by the observer. Sightings of unusual aerial phenomena date back to ancient times, but UFOs (sometimes called flying saucers) became widely discussed only after the first widely publicized American sighting in 1947. Many thousands of such observations have since been reported worldwide.

At least 90 per cent of UFO sightings can be identified as conventional objects, although time-consuming investigations are often necessary for such identification. UFOs most often turn out to be bright planets or stars, aircraft, birds, balloons, kites, aerial flares, peculiar clouds, meteors, and satellites. The remaining sightings can probably be attributed to other mistaken sightings or to inaccurate reporting, hoaxes, or delusions, although to disprove all claims made about UFOs is impossible.

From 1947 to 1969 the United States Air Force (USAF) investigated UFOs as a possible threat to national security. A total of 12,618 reports were received, of which 701 reports, or 5.6 per cent, were listed as unexplained. The USAF concluded that “no UFO reported, investigated, and evaluated by the Air Force has ever given any indication of threat to our national security.” Likewise, in the United Kingdom an investigation into UFOs by the Ministry of Defence, completed in 2000 but not published until 2006, concluded that “no evidence exists to suggest that the phenomena seen are hostile or under any type of control, other than that of natural physical forces.”

Some people nevertheless believe that UFOs are extraterrestrial spacecraft, even though no scientifically valid evidence supports that belief. The possibility of extraterrestrial civilizations is not the stumbling block; most scientists grant that intelligent life may well exist elsewhere in the universe. A fully convincing UFO photograph of a craft-like object has yet to be taken, however, and the scientific method requires that highly speculative explanations should not be adopted unless all of the more ordinary explanations can be ruled out.

UFO enthusiasts persist, however, and some people even claim to have been abducted and taken aboard UFOs. (A close encounter of the third kind is UFO terminology for an alleged encounter between human beings and visitors from outer space.) No one has produced scientifically acceptable proof of these claims.

Condon, Edward U(hler) (1902-1974), American physicist, noted for his work in quantum theory, nuclear reactions, and the spectra of atoms and molecules. He was born in Alamagordo, New Mexico, and educated at the University of California at Berkeley. From 1928 to 1937 he taught physics at Princeton University. He was one of the early supporters of the atomic bomb programme. Between 1943 and 1945 he worked at the University of California on the electromagnetic separation of uranium-235. He became Professor of Physics and Fellow of the Joint Institute for Laboratory Astrophysics at the University of Colorado in 1963. Between 1966 and 1969 he was also a scientific director of the government-financed investigation into unidentified flying objects.