Sighting in Bois-Guillaume, August 12, 2012

During the night of 11 to 12 August 2012, at about 12:25 a.m., a witness who was looking at the sky noticed an object below the constellation Cassiopeia, moving at low altitude toward the west. As it came closer to the roof of the apartment building, it became easier to see. The witness described it as dark, with a pale, white luminous circle at each of the three points of a triangle. The centre of each circle was dark, almost as dark as the object itself, which barely stood out against the night sky. The object moved silently, then passed over the roof and the witness could no longer see it. Only one account was collected.

The investigation linked the white lights to Thai lanterns carried by the wind. The direction of travel matched the wind direction that night, and a weekend night in August is a likely time for festivities involving lantern releases. The dark centre of the circles also fits: seen from below, a lantern's burner forms a dark disc. GEIPAN considered this a classic case of false shape perception, in which the eye fills the space between isolated points of light with a familiar figure, here a triangle. The apparent thickness of its edges would come from the thickness of the lanterns, which are cylindrical. The case was classified B, Thai lanterns.