“A rainbow around the sun”: what is the solar halo, this exceptional phenomenon observed in the Alps this weekend ?

Un halo solaire MAXPPP – Aurelien Morissard

Ce dimanche 16 juin dans l’après-midi, un drôle de phénomène a suscité la curiosité des habitants du Rhône et de l’Isère.

Un phénomène aussi spectaculaire qu’inhabituel a été observé dans le ciel alpin dimanche vers 14 h.

This is  "solar halos", explains Aurélien Miguet, amateur meteorologist, with France 3. " In Isère, we could observe them from the north of the department up to ax Terresfroides". These solar halos are rings of white or rainbow light sky around the sun which appears in broad daylight.

🌈 Le ciel nous offre un magnifique spectacle actuellement avec ce magnifique arc en ciel horizontal et un halo solaire. Visible probablement sur une grande partie du département !! @CDIsere @KeraunosObs pic.twitter.com/iPmaQG8GVO

— Météo Centre-Isère (@MeteoIsere) June 16, 2024

Observable all year round

“These phenomena are linked to a certain type of clouds, located between 7 000 and 8 000 meters above sea level. altitude: cirrostratus clouds, composed of ice particles. When the sun's rays meet these crystals, the light is diffracted and the halo appears", explains the head of the Météo France center in the Northern Alps, Denis Roy, to our colleagues.

These phenomena are observable all year round, they can happen in the evening as well as during the day. "Even though they are necessarily more numerous in winter and autumn", explains the manager. "These are common phenomena, some are more marked than others."