ICE ICE BABIES Crewmembers from the U.S. Coast Guard cutter Healy take measurements of sea ice off of Barrow, Alaska as part of their ongoing ICESCAPES study looking at the impact of climate change on the Arctic and Pacific Oceans. (Photo: NASA via The Guardian)
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.