halo of 46°
in the form of a circle, or portion of a circle, with an angular radius of about 46° about a light
source, such as the sun or moon.
The coloration is reddish on the inner edge to bluish on the outer edge. This halo is much less common that the halo of 22°
. The 46° halo is explained by the refraction
of light passing through the 90° prism formed between the side and basal faces of a hexagonal ice crystal
. The minimum angle of deviation
for this ice
prism is about 46°. Closely associated with this halo are the 46° infralateral arcs and the 46° supralateral arcs. In particular, the shape of the 46° supralateral arc often follows the uppermost parts of the 46° halo so closely that the two are almost impossible to distinguish. In fact, upon examination, a large fraction of the halos commonly interpreted as being 46° halos turn out to be pieces of 46° supralateral arcs. Which of the two halos (46° halo or 46° supralateral arc) is more frequent has not been settled.
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