- Project Blue Book (Wikipedia)
Project Blue Book was the code name for the systematic study of unidentified flying objects by the United States Air Force from March 1952 to its termination on December 17, 1969. The project, headquartered at Wright-Patterson Air Force Base, Ohio, was initially directed by Captain Edward J. Ruppelt and followed projects of a similar nature such as Project Sign established in 1947, and Project Grudge in 1949. Project Blue Book had two goals, namely, to determine if UFOs were a threat to national security, and to scientifically analyze UFO-related data.
- Binary Star § Astrometric binaries (Wikipedia)
Astronomers have discovered some stars that seemingly orbit around an empty space. Astrometric binaries are relatively nearby stars which can be seen to wobble around a point in space, with no visible companion. The same mathematics used for ordinary binaries can be applied to infer the mass of the missing companion. The companion could be very dim, so that it is currently undetectable or masked by the glare of its primary, or it could be an object that emits little or no electromagnetic radiation, for example a neutron star.