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   Subhorizon arcs



Halos beneath the sky.
A subsun, sub parhelia, subparhelic circle and a subcircumzenithal arc shine below the horizon. Continuations of 'ordinary' arcs go beneath the horizon also. Fisheye simulation centered on the horizon, sun 10� high.

Imagine a halo display mirrored in a lake. Subhorizon halos are similarly formed except that the mirroring is inside the very crystal making the halo. An extra reflection from a lower horizontal face produces the subhorizon counterpart of an ordinary plate crystal halo.

No multiple scattering or reflection by separate crystals is needed.

Subtleties of the refraction and ray paths make subhorizon arcs very similar to but not identical to their above horizon counterparts.

Look for subhorizon halos from aircraft, hills or mountains. Sometimes they can even be seen in snow and ground frosts.