GIEN-SUR-CURE (58) 24.05.2017

On 24 May 2017, after an evening observing Jupiter with a group of astronomers at Gien-sur-Cure, 2 witnesses noticed a very bright point moving in an unusual way from south-southeast to east-northeast before receding and disappearing. GEIPAN considers that they very probably saw the International Space Station. The ISS was in the reported directions at both the beginning, high in the south-southeast, and the end, on the east-northeast horizon. The reported end time of 23:45 is 8 minutes later than the ISS passage ended at 23:37. GEIPAN suggests that the witness checked the watch after the observation had ended, that the watch was fast, or both. Given the ISS's movement and brightness, far greater than any star, GEIPAN considers it impossible that people deliberately watching a clear, starry sky would have failed to see it. The reported curved path initially seems inconsistent with a satellite. However, GEIPAN interprets the account as a familiar perceptual error: changes in brightness were taken to indicate approach or recession along the line of sight. Thus the apparent curve was imagined toward the witnesses rather than seen as rapid changes in azimuth and elevation. Their descriptions illustrate this: - Witness 1: “It descended toward us while growing larger”; then “the ball moved away very quickly toward the north/northeast, rising high in the sky until it became the size of a star, then a tiny bright point that was barely discernible, then nothing.” - Witness 2: “A luminous, moving object heading toward us”; a “diving arrival”; then “it moves straight away in front of us without descending or climbing, and disappears.” Witness 2's reconstruction drawing in the questionnaire shows a UAP coming from east-southeast directly toward the witnesses, then turning and departing straight toward east-northeast. GEIPAN explains that a witness cannot directly detect radial movement by an unknown object, but can only infer it, often incorrectly, from simultaneous changes in apparent size or brightness. Here the ISS may have brightened sharply as it reached maximum brightness high in the east-southeast, creating the apparent diving phase, before fading, probably more slowly than it had brightened. GEIPAN classifies the case A: the International Space Station.