ESPEDAILLAC (46) 21.01.2017

A witness at Espédaillac (46) reported several observations of multicoloured lights apparently moving unpredictably in the night sky during January and February 2017. One was observed by him, his partner and 2 gendarmes who came to the scene. Telephone discussions with one gendarme and then the main witness allowed GEIPAN to identify Arcturus as the object seen jointly from 00:50 to 01:40 on 24 January. The elevations and azimuths the witness supplied by phone matched Arcturus, which moved between 14° and 25° elevation and azimuths 75°–85° in the east. Its perceived brightness relative to other stars also matched. GEIPAN explains that this star is often misidentified at low elevation. The thick layer of atmosphere along the line of sight and atmospheric turbulence cause scintillation, producing changing colours and an impression of movement. An even stronger impression can arise from the autokinetic effect, especially when a point of light is watched intently; the source refers to an article on that effect. The other reports also matched stars known to produce such mistakes, reinforcing the explanation. Around 20:00, a similar effect in roughly the same area of sky was associated with Procyon. The sighting at 02:30 on 27 February, in the opposite azimuth direction at 250° from the other side of the house, could be explained by Sirius at 15° elevation. GEIPAN consequently identified the series as observations of stars, though not always the same star.