A mass sighting is an episode in which many people report unusual lights or objects over the same general area and period. The label can cover a concentrated event lasting minutes, a sequence of observations across several hours, or a regional wave extending for days or months. Multiple witnesses can provide independent directions, times, images, and descriptions, but a large witness count does not by itself show that everyone saw one object or that each report has the same cause.

The 1952 Washington UFO wave combined visual reports with radar returns around the capital on two July weekends and provoked an Air Force press conference. The Belgian UFO wave, beginning in 1989, accumulated civilian, police, and military reports over many months. During the 1997 Phoenix Lights, witnesses across Arizona described a broad formation of lights, while later stationary lights near Phoenix were widely associated with military illumination flares. These cases remain culturally linked even though their evidence, duration, and proposed explanations differ.

Mass sightings are valuable when accounts can be synchronized. Investigators can map sight lines, compare angular motion, check air traffic and astronomical conditions, recover original photographs, and determine whether reports were made before media coverage influenced later recollections. They are harder to interpret when times are rounded, positions are missing, witnesses confer, or several stimuli occur in succession. Apparent size and distance are especially uncertain at night, when isolated lights provide few depth cues. Radar or video adds information only if its calibration, location, and timing can be matched to the visual reports.

The category matters because it challenges the idea that all anomalous reports are private or purely psychological, yet it also shows how collective events acquire simplified legends. A wave can contain conventional aircraft, celestial objects, flares, hoaxes, and unresolved observations at once. Historical archives preserve thousands of such reports, but each episode still turns on the quality and independence of its records. “Mass sighting” describes the social and observational scale of an event; it is not a conclusion about the identity or origin of what people reported.