For centuries, mankind has reported seeing UFOs in various parts of the world. The alleged sightings have captivated the public imagination and raised questions about life beyond our planet.
Early cave drawings, ancient texts and centuries-old paintings appear to depict or describe human contact with extraterrestrial beings and UFOS, or unidentified flying objects. For instance, the 1710 painting by Dutch artist Aert De Gelder appears to show a UFO illuminating the baptism of Jesus Christ.
In modern times, purported sightings of UFOs have captured headlines and newscasts worldwide. Most recently, media attention turned to an audio recording released by the Federal Aviation Administration in which two pilots flying on different aircraft above Arizona in late February report having close encounters with a mysterious object.
According to the FBI, a "rash of sightings" of UFOs swept the United States in 1947, after World War II amid a heightened interest in aerospace flight and technology. The FBI says it helped investigate the claims between 1947 and 1954.
"Although the newly formed U.S. Air Force was the primary investigator of these sightings, the FBI received many reports and worked for a time with the Air Force to investigate these matters," the agency says on its website, where records of some of the reports are published.
Perhaps the most famous incident took place northwest of Roswell, New Mexico, in the summer of 1947, when a foreman of a ranch came across mysterious debris, including metal rods and paper-thin, metallic-looking scraps. The man, William Brazel, reported the strange wreckage to the local sheriff, who contacted the nearby Roswell Army Air Field.
Maj. Jesse Marcel and other intelligence officers were sent to recover the materials, according to the Roswell Daily Record.
A public information officer for the Roswell Army Air Field then released a statement saying officers had retrieved a "flying disc," which had crashed on the ranch near Roswell.
Military officials later retracted the statement after investigating the debris, saying it was actually remnants of a downed weather balloon.
"I am sure what I found was not any weather observation balloon," Brazel told the newspaper in an interview in July 1947.
Since the incident near Roswell, a number of non-governmental organizations were set up to investigate alleged UFO sightings. The Mutual UFO Network (MUFON), founded in 1969, is said to be the oldest and largest in the United States. The Ohio-based nonprofit catalogs and probes cases of purported sightings from around the world.
MUFON recorded 7,651 worldwide reports of UFO sightings in 2017, according to its database. It has more than 800 reports so far this year.
The National UFO Reporting Center (NUFORC) has been recording and investigating alleged sightings and contacts with extraterrestrials since 1974. People who have submitted reports to the Washington state-based group claim to have seen an unexplainable object, often making no audible sounds as it moves in the sky, emits beams of light or changes color.
One woman reported seeing "small, metallic spheres in the sky" while looking out her kitchen window in Nooksack, Washington, in the afternoon of March 19. She thought they were birds at first until they began to weave through dark clouds and they reflected the sun, the woman said in her report to NUFORC.
"As I watched the objects, I observed them moving up and down in and out of the clouds, as well as side to side," she wrote. "Then they were gone. They disappeared into the clouds and I haven't seen them since."
Speaking to ABC News late last year, retired U.S. Navy Cmdr. David Fravor described seeing a 40-foot-long wingless object during a routine training mission off California's coast on Nov. 14, 2004. The former pilot recalled how the object flew at incredible speeds in an erratic pattern, though he said it had no exhaust trail in infrared scanning.
"I can tell you, I think it was not from this world," Fravor told ABC News in an interview in December 2017. "I'm not crazy, haven't been drinking. It was —- after 18 years of flying, I've seen pretty much about everything that I can see in that realm, and this was nothing close."
Fravor's retelling of this bizarre encounter came after the U.S. Department of Defense confirmed to ABC News that it ran a program for investigating reports of UFOs for years. The once-secret program was funded from 2007 to 2012. According to The New York Times, the Department of Defense spent $22 million on the endeavor.
"The Advanced Aviation Threat Identification Program ended in the 2012 time frame," the Pentagon told ABC News in a statement on Dec. 16, 2017. "It was determined that there were other, higher priority issues that merited funding and it was in the best interest of the DoD to make a change. The DoD takes seriously all threats and potential threats to our people, our assets and our mission and takes action whenever credible information is developed."
More recently, the Federal Aviation Administration released the audio recording of a conversation between air traffic control and two pilots on different aircraft who both reported having close encounters with a mysterious object flying high above southern Arizona within minutes of each other on Feb. 24.
"Something just passed over us," one of the pilots says to the Albuquerque Air Route Traffic Control Center. "I don't know what it was."
A spokesperson for the FAA told ABC News that the controller was unable to verify that any other aircraft was in the area at the time of the reported sightings.