|Clouds over the dunes. Looking west, towards the sun.|
|10 minutes later, looking northwest.|
|Ice halo, just before sunset.|
|5 minutes later. As the sun drops behind the hills, the rays stand out more vividly.|
Light passing through the hexagonal ice prisms is deflected twice, which produces deviation angles ranging from 22° to 50°. Lesser deviation results in a brighter halo along the inner edge of the circle, while greater deviation contribute to the weaker outer part of the halo. As no light is refracted at smaller angles than 22° the sky is darker inside the halo. (from Wikipedia)
|(Diagram from the University of Illinois WW2010 Project.)|
The border of the halo is 22° from the sun, here at the horizon. Just at this border, a rainbow effect is visible, with the red on the interior, the blue on the outer edge.
This halo is combined with a ray pattern, and a lower-lying cloud which distorts some of the rays.
|Zooming in, to see the textures (faintly) in the lower layer of ice and clouds.|