The Great Wilmington Blue Light incident was reported to have occurred on July 13, 1860, during the evening hours directly over the city of Wilmington, Delaware, and was documented in the Wilmington Tribune on July 30 of the same year. The event was described as brief in duration, lasting approximately one minute, during which a luminous aerial object traversed the city at low altitude.

The object was described by witnesses as a large, structured form rather than an indistinct light, with an estimated length of approximately 200 feet and an elongated, serpentine or cigar-like shape. It emitted a pale blue light of sufficient intensity to illuminate the streets and buildings below as it passed, with the illumination described as engulfing the city during its transit. At the rear of the object, sparks or fire were observed, described in contemporary terms as resembling the discharge from a rocket.

Trailing the primary object, three red, glowing spheres were observed maintaining exact intervals of approximately 100 feet between each, forming a precise and consistent line behind the lead object. During the course of the sighting, a fourth red sphere was reported to shoot out from the rear of the primary object and then slow to join the formation, taking position alongside the others at the same measured interval.

The object was observed to travel on a level course at an estimated altitude of approximately 100 feet above the ground, an extremely low elevation, moving at a steady and deliberate pace sufficient to cross the city within the reported duration while remaining slow enough for observers to distinguish and count the trailing objects. Its path carried it across Wilmington, after which it turned toward the southeast, passed directly over the Delaware River, and continued eastward until it disappeared from view.

Contemporary reporting extended beyond local account, with the event recorded in the Wilmington Tribune and noted in scientific discussion of the period as more than rumor. Explanations proposed at the time included atmospheric electricity and meteor activity, though it was observed within these discussions that meteors do not maintain level flight at such low altitude nor produce smaller objects that separate and proceed in organized formation. The conditions of the sighting occurred during a period in which known aerial phenomena were limited to natural or primitive man-made sources, such as birds, clouds, and hot air balloons, which were not understood to exhibit the described characteristics. The incident remains recorded as an anomalous aerial observation.