Black triangles are UFOs reported as having a triangular shape and dark color, typically observed at night, described as large, silent, hovering, moving slowly, and displaying pulsating, colored lights and can turn their lights off. British sightings and UK Ministry of Defence Report A declassified report from the UK Ministry of Defence, addressing Unidentified Aerial Phenomena (UAP) within the UK Air Defence Region and code named Project Condign, includes analyses of black triangle sightings. The report includes the statement that "the majority, if not all, of the hitherto unexplained reports may well be due to atmospheric gaseous electrically charged buoyant plasmas" that are "capable of being transported at enormous speeds under the influence and balance of electrical charges in the atmosphere." The report also notes that "at least some" of the black triangle observations likely arise from meteor entry into the atmosphere. Regarding the triangular shapes, the report also states: "Occasionally ... it seems that a field with, as yet, undetermined characteristics, can exist between certain charged buoyant objects in loose formation, such that, depending on the viewing aspect, the intervening space between them forms an area (viewed as a shape, often triangular) from which the reflection of light does not occur. This is a key finding in the attribution of what have frequently been reported as black 'craft,' often triangular and even up to hundreds of feet in length." A recommendation in the report is that no attempt be made on the part of aircraft to intercept or outmaneuver these objects, and instead to place them astern to mitigate the risk of collision. The report also speculates that the hypothesized plasma formations, through their "magnetic, electric or electromagnetic" fields, could have the potential to induce in observers vivid, but mainly incorrect, perceptions. The Project Condign report was not peer reviewed, and some authors have cast doubt on its scientific veracity. Other sightings 1980s Hudson Valley sightings During the early 1980s several hundred people claimed to have witnessed UFOs flying over, or near to, the Hudson River in New York state. These sightings involved hovering or slowly-flying, V-shaped objects rimmed with colorful lights. Several pilots claimed responsibility for these UFOs, reporting that the objects, some of which were tracked to a local airport and parking lot, were ultralight aircraft flown in formation. 1989–1992 Belgian wave The Belgian UFO wave began in November 1989. The events of 29 November were documented