Select Text Level:

On 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.
aircraft
Noun

vehicle able to travel and operate above the ground.

Air Force
Noun

nation's military aviation forces.

associate
Verb

to connect.

civilian
Noun

person who is not in the military.

Noun

visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

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.

concern
Verb

to worry or take an interest in.

discover
Verb

to learn or understand something for the first time.

evening star
Noun

planet seen in the western sky soon after sunset, usually Venus.

evidence
Noun

data that can be measured, observed, examined, and analyzed to support a conclusion.

experimental
Adjective

having to do with a test or trial version.

extraterrestrial
Adjective

located or formed outside Earth's atmosphere.

intelligence
Noun

ability to learn and understand.

investigate
Verb

to study or examine in order to learn a series of facts.

military
Noun

armed forces.

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.

Noun

large, spherical celestial body that regularly rotates around a star.

prototype
Noun

early version or model.

puzzle
Verb

to confuse or baffle.

record
Verb

to preserve observations with notes, drawings, photographs, audio or video recordings.

rival
Noun

opponent.

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.

spacecraft
Noun

vehicle designed for travel outside Earth's atmosphere.

technology
Noun

the science of using tools and complex machines to make human life easier or more profitable.

UFO
Noun

(unidentified flying object) any unexplained moving object observed in the sky.

Noun

state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

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.