Black triangles are a class of unidentified flying objects, or UFOs, with certain common features which have reportedly been observed during the 20th and 21st centuries. Media reports of black triangles originally came from the United States and United Kingdom. The aircraft may be related to the rumored USAF Aurora aircraft developmental program.
Reports generally describe this class of UFOs as large, silent, black triangular objects hovering or slowly cruising at low altitudes over cities and highways. Sightings usually take place at night. These objects are often described as having pulsing colored lights that appear at each corner of the triangle.
Black triangle UFOs have been reported to be visible to radar, as was the case with the famous Belgian UFO wave. During these incidents, two Belgian F-16s attempted to intercept the objects (getting a successful missile lock at two occasions) only to be outmaneuvered; a key conclusion of the Project Condign report was that no attempt should be made on the part of civilian or RAF Air Defence aircraft to outmaneuver these objects except to place them astern to mitigate the risk of collision. This entire Belgian UFO wave, however, has been disputed by skeptics.
Declassified research (subject to a Freedom of Information request) from the UK Ministry of Defence report UAP in the UK Air Defence Region, code named Project Condign and released to the public in 2006, draws several conclusions as to the origin of "black triangle" UFO sightings. Their researchers conclude that most, if not all, "black triangle" UFOs are formations of electrical plasma, the interaction of which creates mysterious energy fields that both light and produce vivid hallucinations in witnesses that are in close proximity. Further it suggests that "the majority, if not all, of the hitherto unexplained reports may well be due to atmospheric gaseous electrically charged buoyant plasmas" which emit charged fields with the capability of inducing vivid hallucinations and psychological effects in witnesses and are "capable of being transported at enormous speeds under the influence and balance of electrical charges in the atmosphere." The researchers note that plasmas may be formed by more than one set of weather and electrically charged conditions, while "at least some" events are likely to be triggered by meteor re-entry in scenarios where meteors neither burn up completely nor impact, but rather break up in the atmosphere to form such a charged plasma. These plasma formations are also theorized to have the effect of refracting light between themselves, producing the appearance of a black polygonal shape with the lights at the corners caused by self-generated plasma coloration (similar to the Aurora Borealis).