Today, around midday, the Sun was seen with a 22° Halo and adjacent a Circumscribed Halo. Both Halo's have the red color towards the center of the Sun.
The 22° and Circumscribed Halo's are developed when Sun light enters one side of a hexagonal columnar ice crystal and exits through another side. The light is refractec when it enters the ice crystal and once again when it leaves the ice crystal. The difference between both Halo's is the fact that 22° Halo are formed within random distributed crystals and Circumscribed Halo's when the crystals are merely horizontal oriented.
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| White = 22° Halo / Blue = Circumscribed Halo |
The shape of the Circumscribed Halo also changes depending the height of the Sun at the sky. When the sun is low, the two “arms” of the upper tangent arc form a sharp angle. As the sun gets higher, they get closer and closer to the 22°-halo. At the same time they become longer, joining the lower tangent arc at a sun elevation of 32°. The complete ring now being formed is called the circumscribed halo. It touches the 22°-halo above and below the sun. First the circumscribed halo is of an oval shape. At increasing sun elevations its shape becomes more and more circular and gets closer to the 22°-halo. At a sun elevation of 70° the circumscribed halo almost covers the 22°-halo.
