Roswell(01 of46)
Open Image ModalAmerica's most infamous UFO case centers in Roswell, N.M. Some people claimed an alien spacecraft crashed there in 1947; the military said it was a weather balloon. (credit:Eric Draper, AP)
Roswell dummies(02 of46)
Open Image ModalThe Air Force issued "The Roswell Report" in 1997. Countering claims that aliens were recovered at the New Mexico site, the report said military officials picked up 200-pound dummies, above, that were used in an experiment. (credit:Air Force / AP)
Sunken Ship in the Baltic Sea(03 of46)
Open Image ModalOn June 19th the Swedish-based diving company Ocean Explorer discovered something they've never quite seen before. They were exploring in the Baltic Sea between Sweden and Finland looking for sunken treasures when a very unusual image suddenly appeared on the sonar. A 197 feet diameter cylinder shaped object was discovered at the depth of approximately 275 feet which resembles the Millennium Falcon from the movie Star Wars. (credit:www.oceanexplorer.se / Everett Collection)
UFO Over Mojave Desert Sept. 9, 1985(04 of46)
Open Image ModalThis cigar-shaped UFO was photographed by general aviation pilot David Hastings as he piloted a Cessna Skymaster plane over the Mojave Desert on Sept. 9, 1985. There has never been an indication of hoax in this case, which remains unexplained to this day. (credit:Courtesy of David Hastings)
UFO Over Holloman Base(05 of46)
Open Image ModalAn unidentified flying object was photographed by a government employee over the Holloman Air Development Center in New Mexico in 1964. Conspiracy theorists have claimed the photo is proof that the U.S. government has been in contact with aliens. (credit:Bettmann / Corbis)
Strange objects over France(06 of46)
Open Image ModalWhile descending an Austrian mountain in 1954, photographer Erich Kaiser captured an image of what he called mysterious silvery-white flying objects. (credit:AP)
Mexican Air Force Pilots Video(07 of46)
Open Image ModalMexican Air Force pilots filmed strange, brightly lit objects that moved quickly in the skies on March 5, 2004. Some scientists said the phenomenon could have been caused by gases in the atmosphere. (credit:AP)
Alien in Brazil(08 of46)
Open Image ModalVideo grab close up. What looks like an alien creature with visible head, neck, arms and body standing in the Brazilian rainforest in Manaus, Brazil.In this Amaz-alien footage, a lone unidentified being appears to stand in the jungle of Brazil -- even arching its back -- just feet away from a bright flashing blue light. In what some allege as proof that Earth is being visited by aliens from another planet, the video was obtained by paranormal writer Mike Cohen who says the video was taken by two British tourists visiting the Manaus region of the Amazon jungle. (credit:Barcroft / Fame)
Crop Circle in Yogyakarta, Indonesia(09 of46)
Open Image ModalA large circle and geometric pattern local residents say were created by a UFO appeared in a rice field in Krasakan hamlet in Sleman, Yogyakarta, on the morning of Jan. 23, 2011. (credit:Tribun Jogja / The Jakarta Post)
Stan Romanek film(10 of46)
Open Image ModalStan Romanek claimed that this still image from a three-minute video he shot in 2003 shows an alien looking into his home in Nebraska. In the film, a strange face appears to be popping up and down outside Romanek's window. (credit:Courtesy Stan Romanek)
Sketch of UFO sighting (11 of46)
Open Image ModalThis eyewitness drawing of an alleged UFO sighting is in one of 19 once-secret files posted to the British National Archives website. The files cover sightings reported between 1986 and 1992. Although many of the reports were debunked, some remain unexplained. (credit:National Archives / PA / AP)
France field markings(12 of46)
Open Image ModalAn investigator in 1989 measures markings that some said were left behind by a UFO in Normandy, France. France began releasing its "X-Files" on UFO sightings in 2007. (credit:CNES / AP)
President Jimmy Carter(13 of46)
Open Image ModalPresident Jimmy Carter, shown here in 1971, reported that he saw a UFO above Leary, Ga., in 1969. He filed a report about the sighting to the International UFO Bureau in 1973. (credit:AP)
Astronaut Gordon Cooper(14 of46)
Open Image ModalAstronaut Gordon Cooper, who piloted Mercury and Gemini space missions in the 1960s, once said he saw a "typical saucer shape, double-cylindrical shape, metallic" UFO. He was also outspoken on the idea that some UFOs were interplanetary vehicles visiting Earth. (credit:AP)
Area 51 (15 of46)
Open Image ModalAt sunset military aircraft contrails in the skies above Area 51 and the U.S.Air Force air weapons range near the town of Rachel and the UFO Highway (hwy. 375) . (CP PHOTO/Larry MacDougal)
Monkey Alien(16 of46)
Open Image ModalA preserved monkey is shown on display in the lobby of the Georgia Bureau of Investigation Crime Lab Thursday July 24, 2008. in Decatur, Ga. The shaved monkey was part of a 1953 UFO hoax in rural Cobb County. (AP Photo/John Bazemore)
Alien(17 of46)
Open Image ModalAlien created for the Showtime movie "Roswell, " and is purported to be a likeness of the alien allegedly found in a crashed 'spaceship' in Roswell, New Mexico in the 1950's. (Photo credit: PA)
UFO(18 of46)
Open Image ModalUnidentified Flying Object sighted over New Zealand's South Island on Jan. 3, 1979. New Zealand television crew cameraman Frank Kazukaitis said of the sighting, "It looked like an illuminated ping pong ball with a tinge of red in the middle." (AP Photo/Dominion)
ET Vistor Center(19 of46)
Open Image ModalWorld reception center for official visitors from outer space was proposed by an American specialist on unidentified flying objects (UFOs). Hungarian-born Colman von Keviczky, a former United Nations official, right, for the effective solution of the global problem. (Photo credit: PA)
UFO(20 of46)
Open Image ModalThis photograph was taken by a tourist and shows an Unidentified Flying Object, flying over Romanian territory near Cluj town Sept. 24. 1968. (AP Photo)
UFO(21 of46)
Open Image ModalEngineer Reg Willard (left) chips away with a chisel as he dissects the bleep mechansim of the mystery object found at Clevedon, Somerset, by a schoolboy. Helping him is Aubrey Willcocks, who was called in by the local police. Looking on is Sergeant John Durston. The object was one of five strange objects, all resembling flying saucers and emitting noises, found in different parts of the country. Inside the object Mr Willard found two Exide batteries, a British made transmitter and a loudspeaker. (Photo credit: PA)
UFO(22 of46)
Open Image ModalEngineer Michael J Willcocks applies the taste test to the liquid found in the mystery object found at Clevedon, Somerset, by a schoolboy. The liquid was later identified as pig swill. The object was one of five strange objects, all resembling flying saucers and emitting noises, found in different parts of the country. (Photo credit: PA)
UFO(23 of46)
Open Image ModalThis is one of three photos of a supposed UFO taken by Rex Heflin, Mar. 28, 1967, Santa Ana, Calif. Heflin is an Orange County highway department investigator. (AP Photo)
Pancake-like objects(24 of46)
Open Image ModalJoseph Simonton, 60 of Eagle River display one of three pancake-like objects, he says were given to him on Saturday by the operator of a 'flying saucer'
UFO(25 of46)
Open Image ModalPickaway County Deputy Sheriff John Wolford supervises the loading of a part from an Air Force balloon that descended from the sky in south central Ohio farmland, April 19, 1966. The balloons, devices and a 4,500-pound payload apparatus, launched at Holoman Air Force Base, N.M., came down in two sections about 15 miles apart. (AP Photo)
(26 of46)
Open Image ModalNorthwestern University Astrophysicist, J. Allen Hynek, shown at a press conference, March 25, 1966, Detroit, Mi. A newsman handed this photo to Hynek and asked him if it was a flying saucer. Hynek described it as a chicken feeder and said that numerous sightings of recent unidentified flying objects in Michigan were probably the result of swamp gasses and not visitors from outer space. Hynek has studied and investigated UFOs for the past 15 years. (AP Photo/ Alvin Quinn)
UFO(27 of46)
Open Image ModalMichael Savage, 15-year-old son of prominent San Bernardino physician and surgeon, was practicing picture-taking with his new camera, when he saw motion out of the corner of his eye Thursday, July 24, 1956, San Bernardino, Calif. He quickly shot this picture, tried to shoot another and in his haste over-cranked the camera, drawing a blank with his second shot. The object disappeared in 30 seconds, he said, not over the horizon but quickly out of sight in the sky. (AP Photo/Michael Savage)
White UFOs(28 of46)
Open Image ModalThis photograph, reproduced from the quarterly UFO periodical Flying Saucers International in Los Angeles, shows silvery white flying objects as seen by photographer Erich Kaiser while descending from Reichenstein mountain in Austria on Aug. 3, 1954. (AP Photo)
UFO Crash(29 of46)
Open Image ModalA wrecked wind turbine on farm land in the village of Conisholme, Lincolnshire. The mysterious severance of the wind turbine blade may have been caused by a mechanical failure, an expert said today. Local residents reported seeing a bright light on the morning it happened, prompting speculation that a UFO had caused the damage. But Fraser McLachlan, chief executive of GCube, which insures more than 25,000 wind turbines worldwide, said that although it is unusual, this type of incident happens about five or six times a year. (Photo credit: Chris Radburn/PA Wire)
UFO Advert(30 of46)
Open Image ModalAn Advertisment for the Irish UFO Society which appears in the 2007 Association of Garda Sergeants and Inspectors Diary. (Photo credit: Niall Carson/PA)
Dead Cattle(31 of46)
Open Image ModalRachel, Nevada, Near Las Vegas on the UFO Highway (hwy 375) at the town of Rachel, dead livestock (cattle) beside the highway. Rachel is near Area 51 which is contained within the U.S.Air Force weapons range. (CP PHOTO/Larry MacDougal)
Space Man(32 of46)
Open Image ModalPolice Officer Jeff Greenhaw took these pictures of a strange looking creature he said he found standing in the middle of a major highway which runs thru his town, Wednesday, Oct. 18, 1973, Huntsville, Al. (AP Photo/Jeff Greenhaw)
Cigar(33 of46)
Open Image ModalTexas farmer Carrell Wayne Watts told a polygraph operator this Polaroid snap shows an alien spacecraft 80 to 100 feet long, Sunday, Feb. 25, 1968, Amarillo, Tx. The Houston Post will release results of 29-year-old Watts lie test late Sunday night. (AP Photo/Carrell Wayne Watts)
Strange noises(34 of46)
Open Image ModalOne of the strange objects, all resembling flying saucers and emitting noises, found in different parts of Britain. This one was found at Chippenham, Wiltshire. (Photo credit: PA)
Civilian or Military Aircraft(35 of46)
Open Image ModalCivilian or military aircraft: Planes can look mysterious at night or in certain light conditions, thus confusing an observer. (credit:Sean Cole, US Navy / Getty Images )
Meteors(36 of46)
Open Image ModalMeteors: Space debris can create a spectacular light show when it burns through the Earth's atmosphere, and sometimes reported as UFOs. (credit:Ethan Miller, Getty Images )
Manufactured UFO -- 2011(37 of46)
Open Image ModalPictured is a quad copter -- a deliberately manufactured UFO created by special effects wizard Marc Dantonio for a National Geographic special, "The Truth Behind: UFOs," which aired in December 2011. On the left is what the small device looks like resting on the ground, measuring 4 feet in circumference. At right, is how it appeared behind a tree in the night sky. (credit:Marc Dantonio / FX Models / YouTube )
Antarctic UFO Closeup -- Aug. 10, 2012(38 of46)
Open Image ModalThis is a closeup of the UFO from the previous slide. No official explanation has been offered about the object. (credit:myunhauzen74 / YouTube )
Antarctic UFO -- Aug. 10, 2012(39 of46)
Open Image ModalA circular UFO hovers above the Neumayer-Station III research facility in Antarctica on Aug. 10, 2012. Theories ranging from a simple weather balloon to a more elaborate ship from another planet have run the Internet gamut. The next slide shows a closeup of the object. (credit:myunhauzen74 / YouTube)
Lanterns(40 of46)
Open Image ModalThese candle-lit Chinese lanterns can rise high into the sky and were mistaken for UFOs in England. (credit:China Photos / Getty Images )
Baltic Sea UFO 3(41 of46)
Open Image ModalOne of several odd stone circle formations, sitting on top of the unidentified object at the bottom of the Baltic Sea. (credit:Expressen.se / YouTube)
Baltic Sea UFO 2(42 of46)
Open Image ModalClose-up of rock bed that forms the Baltic Sea UFO, which still mystifies researchers. (credit:Expressen.se / YouTube)
Baltic Sea UFO 1(43 of46)
Open Image ModalAn image released on June 15, 2012, shows a close-up view of the unidentified object sitting on the bottom of the Baltic Sea. (credit:Expressen.se / YouTube)
Blimps or Advertising Balloons(44 of46)
Open Image ModalBlimps or advertising balloons: These can look like flying saucers from some angles, especially at night. (credit:Lars Baron, Bongarts / Getty Images)
Clouds(45 of46)
Open Image ModalClouds: Saucer-shaped or "lenticular" clouds that form at high altitudes have been confused with UFOs. (credit:Getty Images)
Weather Phenomenon(46 of46)
Open Image ModalSome UFO sightings may be due to a natural phenomenon known as sprites, like this one shown from 2006. "Lightning from [a] thunderstorm excites the electric field above, producing a flash of light called a sprite," said geophysicist Colin Price. (credit:ILAN Science Team / Space.com)