Colourful supralateral and infralateral arcs
form when rays pass between the side and basal (end) faces of singly
oriented hexagonal columns.
The filtered right hand simulation shows only rays which have passed
through an end face and so isolates the supralateral (upper) and infralateral
(lower) arcs. The unfiltered simulation at left also has a bright
upper tangent arc and parhelic circle produced by the same column
crystals. Some poorly oriented crystals were added to make the 22°
brightly coloured arcs are usually seen only as fragments.
They change their shapes dramatically with changes in solar altitude.
The supralateral arc, like the related circumzenithal arc, only forms
at solar altitudes below 32°.
Small sections can be difficult to distinguish from
halo and most of the 46° halos reported are probably