A Liljequist parhelion is a rare halo, an optical phenomenon appearing on the parhelic circle approximately ±150-160° from the sun between a 120° parhelion and the anthelion (opposite to the sun at the antisolar point).
While the sun touches the horizon, a Liljequist parhelion is located approximately 160° from the sun and is about 10° long. As the sun rises up to 30° the phenomenon gradually moves towards 150°, and as the sun reaches over 30° the optical effect vanishes. The parhelia are caused by light rays passing through oriented plate crystals.[1] Like the 120° parhelia, the Liljequist parhelia displays a white-bluish colour. This colour is, however, associated with the parhelic circle itself, not the ice crystals causing the Liljequist parhelia. [2]
The phenomenon was first observed by Gösta Hjalmar Liljequist in 1951 at Maudheim, Antarctica during the Norwegian-British-Swedish Antarctic Expedition in 1949-1952. It was then simulated by Dr. Eberhard Tränkle (1937-1997) and Robert Greenler in 1987 and theoretically explained by Walter Tape in 1994.[1]