This phenomenon occurs when sunlight encounters suspended luminous crystals, present in a certain type of cloud. A halo forms, for a few minutes or a few hours, around the star, before disappearing. This Sunday, June 16, a few lucky people were able to observe them in Isère.
You may have seen this luminous phenomenon on Sunday June 16 in the Isère sky. The formation of a large ring of white or rainbow light around the Sun in broad daylight. “They are solar halosexplains Aurélien Miguet, amateur meteorologist and administrator of the X Météo Centre-Isère page. We were able to observe them from the north of the department to the Cold Lands.”
“These phenomena are linked to a certain type of clouds, located between 7,000 and 8,000 meters above sea level: cirrostratus, composed of ice particlessays Denis Roy, head of the Météo France center in the Northern Alps. When the sun’s rays meet these crystals, the light is diffracted and the halo appears.
In other words, it is the contact between light and suspended crystals that causes this optical phenomenon. “It’s like when you place a prism in front of a light source: it diffracts the light into lots of colors”notes the specialist. “We can see a rainbow around the Sun”adds Aurélien Miguet.
For Météo France experts, the appearance of cirrostratus heralds a “cloudy”. These clouds appear “generally before a disturbance: this does not mean that there will absolutely be rain, it may fall a little nearby”, specifies Denis Roy. Solar halos evaporate after a few minutes or hours.
The halo phenomenon can also be observed at night, around the Moon. Drawing.
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© PASCAL POCHARD-CASABIANCA / AFP
They can be observed throughout the year, in France, “even if they are necessarily more numerous in winter and autumn”. “We can also see them at night, around the Mooncontinues the manager. These are common phenomena, some are more marked than others. But we don’t monitor them like the Northern Lights.”
