An anthelion (plural anthelia, from late Greek ανθηλιος, "opposite the sun") is a rare optical phenomenon appearing on the parhelic circle opposite to the sun as a faint white halo, not unlike a sundog.

How anthelions are formed is disputed. Walter Tape, among others, has argued they are not separate haloes, but simply where various haloes caused by horizontally oriented column-shaped ice crystals coincide on the parhelic circle to create a bright spot. If this theory is correct, anthelia should only appear together with these other haloes.^[1]

However, anthelia occurs unaccompanied by other plate crystal haloes, why other scientists have produced alternative explanations. The Dutch professor S.W. Visser proposed they form by two exterior light reflections in quadrangular prisms, while Robert Greenler has suggested two interior reflection in column-shaped crystals produces the phenomenon.^[1]

While the anthelion area is usually sparse on haloes, in a complex display it features various rare optic phenomena: Flanking the anthelion on the parhelic circle are two 120° parhelia (and two Liljequist parhelia) caused by plate crystals. The Tricker and diffuse arcs are produced in singly oriented column crystals and form a Ankh-like shape passing through the anthelion. Wegener arcs occasionally crosses the sky to converge in the anthelion.^[2]

See also

• Antisolar point
• Glory
• Liljequist parhelion
• Optical phenomenon
• Parhelion
• Rainbow
• Subparhelic circle

References

1. ^{a b} Anthelion (English). Arbeitskreis Meteore e.V.. Retrieved on 2007-04-22.
2. Les Cowley. South Pole Halos - Anthelic View. Atmospheric Optics. Retrieved on 2007-04-22. (including fish eye photo a.o.)

External links

• Earth Science Picture of the Day, April 26, 2006 - Photo of an anthelion and anthelic arcs display in Germany February 2006.

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Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Anthelion". Image Credit.

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