An account in Var, France

On May 27, 2016 at 4:26 p.m., a witness lying on the beach at Les Salins is intrigued by a particular phenomenon in the sky crossed by an airplane condensation trail. The witness describes a straight shape, black or very dark gray in color, resembling a "kind of smoke curtain" visible from the ground to the sky. The phenomenon is motionless. The witness hears no particular noise. He films the phenomenon. Only one testimony will be collected. Analysis of the testimonial elements, photographs, and video provided by the witness indicates that the strange character of the observation results from a natural phenomenon known as a "volumetric shadow seen edge-on" ("edge shadow" in English). This phenomenon occurs and becomes visible when a straight airplane condensation trail passes in front of the sun and there is a sun/trail/observer alignment. From then on, a cast shadow appears over the entire volume of atmosphere contained in the planar slice delimited by the trail, the observer, and the sun (see the investigation report). This slice of atmosphere behaves like a slightly tinted pane of glass, which one does not notice if looking at it head-on but which makes a dark streak for the one observing it from the side (or edge-on). This streak is all the darker the longer the pane is, that is, here, the longer the straight part of the trail is. As soon as the observer is not located in this slice, the dark character disappears and the phenomenon with it. The latter therefore requires particular conditions that were all met here for the witness. The dark streak created is present over the entire height of the witness's line of sight, including therefore in the sky. The witness who notices the airplane trail in the sky can imagine the direct (or classic) shadow cast on the ground by this trail but much less a shadow in the sky. Consequently, GEIPAN classifies the case as A: airplane trail, volumetric shadow seen edge-on.