An account in La R�union, France

On August 21, 2015 at 2 a.m. on Reunion Island, a witness photographs a phenomenon in the sky that intrigues him. The witness reports having seen a conical bluish luminous shape surrounded by a halo. Only one testimony was collected. This observation of a large translucent luminous phenomenon moving slowly in the sky is quite exceptional, and moreover the quality of the photos taken by the witness makes it possible to characterize it perfectly. Due to the resemblance to other similar phenomena (see the article on a luminous halo in the sky of the Indian Ocean on Sept 29, 2013), the investigation quickly turned toward the search for recent satellite launches. Indeed, after investigation, the position of the object in the sky is consistent with the trajectory of the cryogenic upper stage of the Ariane VA225 launcher, launched from Kourou on 20/08 at 20:16 UTC; this stage, catalogued as N40876, began its passivation (tank draining) at 21:12; it passed vertically over Indonesia at more than 8000 km altitude (see attached map). Around 21:30 UTC (time the photo was taken), the object was indeed visible from Reunion Island. Since this is a geostationary satellite launch on a highly elliptical transfer orbit (about 300 km–36,000 km), the launcher is at that moment already at very high altitude, therefore visible from a very large area. The cloud's own trajectory is close to that of the launcher, but disturbed by the gas ejection velocity, which is difficult to model. The gas cloud released by the passivation could persist until its dilution in space. The halo observed is the cloud of unused gas ejected by the launcher after the propulsion phase; it is lit by the sun and becomes visible to ground observers who are in the night. The GEIPAN classifies this case "A" as a perfectly identified phenomenon: gas cloud from the passivation of the cryogenic upper stage (ESC-A) of the Ariane VA225 launcher.