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A ad POO ney ae é UNIDENTIFIED FLYING OBJECT, a moving aerial or celestial phenomenon, detected visually or by radar but whose nature is not immediately understood. Interest in unidentified flying objects (UFO’s) stems from speculation that some of them are the products of civilizations beyond the earth, and from the psychological insights into contemporary human problems that this inter- pretation provides. Observations. - Unidentified flying objects have been described variously as rapidly mov- ing or hovering; disc-shaped, Cigar-shaped, or ball-shaped; moving silently or noisily; with a fiery exhaust, or with no exhaust whatever; ac- companied by flashing lights, or uniformly glow- ing with a silvery cast. The diversity of the observations suggests that UFO’s have no com- mon origin and that the use of such terms as UFO’s or ‘‘flying saucers’’ serves only to con- fuse the issue by grouping generically a variety of unrelated phenomena. In the United States, popular interest inun- identified flying objects began on June 24, 1947, when a group f rapidly moving, glistening ob- jects was observed from the air in daytime, near Mount Rainier, Washington. The observer, a Seattle resident, dubbed them ‘‘flying sau- cers.’’ The si hting received extensive public- ity. Somewhat similar sightings have been reported ever Since. The differences among these observations, however, are as Striking as the observations themselves. Investigations.-Because of its national de- fense responsibility, the U.S. Air Force inves- tigates reports of unidentified flying objects over the United States. The number of sightings investigated by the Air Force inthe period 1947- 1965 varied greatly from year to year. UFO SIGHTINGS INVESTIGATED BY U.S. AIR FORCE 1947-1950 577 1956-1960 3,350 1951-1955 2,880 1961-1965 2,912 Source: Tacker, L.J., Flying Soucers and the U.S. Air Force (Princeton 1960) ond Library of Congress, Focts About Unidentified Flying Objects (Washington 1966). ; Evaluation of these reports is difficult. Ob- servations frequently are sketchy, and different reports of the same phenomenon are often dis- _ similar, or even irreconcilable. Observers tend to exaggerate. Deliberate hoaxes, some involving double-exposure photography, have been perpe- trated. Z y vir! Most UFO’s have been identified as belong- ing to one of the following categories: uncon- ventional aircraft; aircraft under uncommon weather conditions; aircraft with unusual exter- nal light patterns; meteorological and other high-altitude balloons; artificial earth Satellites; flocks of birds; reflections of searchlights or headlights off clouds; reflection of sunlight from shiny surfaces; luminescent organisms (includ- ing one caSe of a firefly lodged between two ad- jacent panes of glass in an airplane cockpit window); optical mirages and looming (a mirage in which images of objects below the horizon appear distorted); lenticular cloud formations; ball lightning; sun dogs; meteors, including green fireballs; planets, especially Venus; bright stars; and the aurora borealis. Radar detection of unidentified flying ob- jects has also occurred occasionally. Many of these sightings have been explained as radar reflections from temperature inversion layers in the atmosphere and other sources of radar ‘fangels.’’ Considering the difficulties involved in tracking down visual and radar sightings, it is remarkable that all but a few percent of the re- ported UFO’s have been identified as naturally occurring-if sometimes unusual-phenomena. It is of some interest that the UFO’s which are unidentified do not fall into uniform categories such aS motion, color, and lighting, but rather run through the same range of these variables as the identified UFO’s. In October 1957, Sput- nik I, the first earth-orbiting artificial satellite, was launched. Of 1,178 UFO sightings in that year, 701 occurred between October and Decem- ber. The clear implication is that Sputnik andits attendant publicity was responsible for many UFO sightings. Earlier, in July 1952, a set of visual and radar observations of unidentified flying objects over Washington, D.C., caused substantial pub- lic concern. Government concern was reflected in the creation in November of that year ofa Special panel to evaluate these reports. The panel was established by the Office of Scientific Intelligence of the Central Intelligence Agency, -and was headed by H.P. Robertson of the Cali- fornia Institute of Technology. The Robertson panel, after a thorough investigation of the UFO reports to that date, concluded that all were probably natural penomena, wrongly interpreted. The most reliable testimony is that of the professional astronomer. Jesse L. Greenstein of S3AIHOUY IWNOILYN 3HL 30 SONIC10H WOus GIINGONdSY