A halo phenomenon that appears as a white, vertically elongated spot of light as far below the horizon as the true Sun is above. It is thus visible only from an aircraft or elevated position. It arises through reflection by horizontal faces of ice crystals and is, in fact, a specific form of sun pillar. Often also known as an undersun. Coloured subsuns ( subparhelia, subsun dogs) may sometimes appear 22° away from a subsun, in the same relative position as parhelia bear to the true Sun. They probably form through internal reflection from horizontal crystal faces.
Subjects: Meteorology and Climatology.