HUNTSVILLE, Ala. – Did you see a halo around the sun this afternoon?
If you did, you spotted an atmospheric optical phenomenon known as a 22-degree halo.
Earthsky.org explains it very simply: “Halos are a sign of high thin cirrus clouds drifting 20,000 feet or more above our heads.”
“These clouds contain millions of tiny ice crystals. The halos you see are caused by both refraction, or splitting of light, and also by reflection, or glints of light from these ice crystals.”
It is called a 22-degree halo because the ring has a radius of approximately 22 degrees around the sun or moon.
According to the site Atmospheric Optics, the halo remains the same diameter no matter what position the sun is found in the sky.
At times, portions of the circle may be missing, so only a segment can be seen.
How sundogs form
Sundogs are a form of atmospheric optics that occur when the sun’s rays pass through ice crystals high in the atmosphere. The ice crystals indicate that moisture is present in the atmosphere, well above the freezing layer.
In the case of sundogs, the ice crystals are oriented in such a way that their large faces are parallel with the ground. This allows sunlight to pass through one of the edges, when it then refracts (or bends). The refraction is occurs at 60 degrees from the edge of the crystal, or 20 degrees from the original path of the sun’s ray if it hadn’t entered the crystal.
The sunlight travels through the crystal and exits out of a different edge, refracting once again. Red light refracts a little more than the blue light, so you see the reddish hue closer towards the sun.
It takes more than one ice crystal to produce a sundog. In fact, the phenomenon that you see occurs because many crystals are present and their sunlight is being directed back to your eyes.
Sun halos and sun dogs can be seen when thin, wispy cirrus clouds are present in the sky. These clouds are often present a few days before an on-coming storm system, or even behind a departing storm system.
If you were able to capture this beautiful phenomena, send us a photo using the link below: