22 Degrees

Taken in Parma, Idaho this spring. The beautiful “sun halo” is an optical phenomenon caused by ice crystals – forming a radius of roughly 22 degrees. Literally several millions of tiny ‘hexagonal’ shaped ice crystals are the reason behind this interesting phenomena. In a hexagonal ice prism, the apex angle is 60 degrees and when light passes through, it is deflected twice leading to deviation angles in the range 22 to 50 degrees. The inner circle is reddish (21.84 degrees – red) and the outer circle is bluish (22.37 degrees – blue). No light is refracted at angles smaller than 22 degrees, so the sky is dark inside the halo! Of course, the sun is very bright – so it shines through at the center!

To create this image, I used a very wide angle lens (14mm), a steady tripod, low ISO (100) and a very small aperture (f22). Wide angle to get the entire halo and background in the frame, tripod to allow me positioning for the right composition and of course stability, low ISO to avoid any noise, small aperture to create ‘sun stars’. Sun stars are created due to diffraction of light as it passes through the tiny lens aperture and the number of “spikes” seen is proportional to the number of diaphragms in the lens aperture.

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