Sighting in Gien-sur-Cure, May 24, 2017

After an evening spent with a group of astronomers observing Jupiter, two witnesses noticed a very bright point of light whose movement struck them as unusual. It was first high in the sky to the south-southeast, then moved away toward the east-northeast, down to the horizon, where it vanished. The sky was starry and cloudless. One witness described a ball that came down toward them while growing larger, then moved away very quickly and climbed, shrinking to the size of a star, then to a small, barely visible point, before disappearing. The other described a bright, moving object arriving in a dive, then heading straight away from them without rising or sinking. Their drawing showed a path coming from the east-southeast, heading straight toward the witnesses, then turning and leaving toward the east-northeast. The witnesses put the end of the observation at 11:45 pm.

GEIPAN's investigation concluded that this was a pass of the International Space Station (ISS), whose positions match both the start and the end of the sighting. Its pass was calculated to end at 11:37 pm; the eight-minute gap was probably due to the witnesses checking their watch some time afterward, or to a watch running fast. The ISS is far brighter than any star and moves, so it is very unlikely that people who had come to watch the sky missed it. The curved path they described reflects a classic error: interpreting a change in brightness as movement toward or away from the observer. The ISS's brightness probably rose sharply to its maximum in the east-southeast, high in the sky, giving the impression of a dive, and then faded. The case was classified A.