Audience versions of this page: FamilyOn December 17, 1969, the United States Air Force closed Project Blue Book, its last program to investigate reports of unidentified flying objects (UFOs).Since its founding in 1947, Project Blue Book recorded more than 12,000 UFO sightings. Military leaders were concerned that some UFO sightings may have been experimental technology developed by the Soviet Union, the U.S.’s rival in the Cold War. Many civilians, on the other hand, associated UFOs with outer space and extraterrestrial intelligence.In the end, Project Blue Book found no evidence of technology “beyond the range of modern scientific knowledge” or threats to national security. Almost all UFO sightings investigated by the program were explained by weather phenomena, existing technology, or experimental technology developed by the U.S. itself. In fact, some of the unusually shaped UFOs spotted over Air Force bases were top-secret prototypes of U.S. aircraft such as the U-2 and A-12 spy planes.
Term Part of Speech Definition Encyclopedic Entry aircraft Noun
vehicle able to travel and operate above the ground.
Air Force Noun
nation's military aviation forces.
person who is not in the military.
visible mass of tiny water droplets or ice crystals in Earth's atmosphere.
Encyclopedic Entry: cloud Cold War Noun
(1947-1991) conflict between the Soviet Union (and its allies) and the United States (and its allies). The two sides never confronted each other directly.
to worry or take an interest in.
to learn or understand something for the first time.
evening star Noun
planet seen in the western sky soon after sunset, usually Venus.
data that can be measured, observed, examined, and analyzed to support a conclusion.
having to do with a test or trial version.
located or formed outside Earth's atmosphere.
ability to learn and understand.
to study or examine in order to learn a series of facts.
national security Noun
programs to protect a nation through economic, social, and political policy.
outer space Noun
space beyond Earth's atmosphere.
phenomena Plural Noun
(singular: phenomenon) any observable occurrence or feature.
large, spherical celestial body that regularly rotates around a star.
Encyclopedic Entry: planet prototype Noun
early version or model.
to confuse or baffle.
to preserve observations with notes, drawings, photographs, audio or video recordings.
Soviet Union Noun
(1922-1991) large northern Eurasian nation that had a communist government. Also called the Union of Soviet Socialist Republics, or the USSR.
vehicle designed for travel outside Earth's atmosphere.
the science of using tools and complex machines to make human life easier or more profitable.
(unidentified flying object) any unexplained moving object observed in the sky.
state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.
Encyclopedic Entry: weather weather balloon Noun
hydrogen-filled balloon equipped with tools to measure temperature, humidity, pressure, and other aspects of the atmosphere.
weather pattern Noun
repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures.