Sighting in Eybens, February 14, 2022

One evening, three witnesses were looking out through the window of their third-floor apartment balcony when they noticed a phenomenon above the ridges of the Belledonne mountain range, to the east. It appeared as a bright circular arc whose apparent diameter, brightness and color resembled those of the Moon. At first the witnesses thought they were looking at the Moon.

After about two minutes, the object gradually shrank while staying motionless above the ridges. During this shrinking, binoculars allowed the witnesses to briefly make out two bright points close together. They then found the Moon in another direction, higher in the sky, which confirmed that what they had seen was something else.

The case was reported through a technical questionnaire and a gendarmerie report. It was rated as having good consistency: several witnesses, a remote investigation followed by an on-site one, and a cognitive interview with one of the witnesses. The explanation retained is the reflection, on the cloud layer, of the powerful floodlights of one or several snow groomers working near L'Alpe d'Huez, possibly close to the Pic Blanc, about 30 km away. The shape matches such a halo, whose lower part is hidden by the ridges, producing an arc. The color is that of the groomers' lights, and webcams show several groomers in the area throughout the observation. The azimuth matches. Météo-France and webcams confirm a cloud layer above 3,300-3,500 m and broken or absent cloud below 2,700 m. A groomer's maneuvers fit the impression of rising and setting, and the lack of noise is explained by the distance. The case was classified A.