An anthelion (plural anthelia, from late
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
ανθηλιος, "opposite the sun") is a rare
optical phenomenon of the
halo
Halo, halos or haloes usually refer to:
* Halo (optical phenomenon)
* Halo (religious iconography), a ring of light around the image of a head
HALO, halo, halos or haloes may also refer to:
Arts and entertainment Video games
* Halo (franchise), ...
family. It appears on the
parhelic circle opposite to the
sun as a faint white spot, not unlike a
sundog, and may be crossed by an X-shaped pair of diffuse arcs.
How anthelia 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.
However, anthelia occur unaccompanied by other plate crystal haloes, thus 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 reflections in column-shaped crystals produces the phenomenon.
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 arc
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
s are produced in singly oriented column crystals and form an
Ankh
Progressive ankylosis protein homolog (ANK ilosis H omolog) is a protein that in humans is encoded by the ''ANKH'' gene.
This gene encodes a multipass transmembrane protein that is expressed in joints and other tissues and controls pyrophosphate ...
-like shape passing through the anthelion.
Wegener arcs occasionally cross the sky to converge in the anthelion.
[ (including fish eye photo a.o.)]
See also
*
Anthelic point
*
False sunrise
*
Glory
*
Liljequist parhelion
A Liljequist parhelion is a rare halo, an optical phenomenon in the form of a brightened spot on the parhelic circle approximately 150–160° from the sun; i.e., between the position of the 120° parhelion and the anthelion.
While the sun touches ...
*
Optical phenomenon
*
Parhelion
*
Rainbow
A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows ...
*
Subparhelic circle
References
External links
Earth Science Picture of the Day, April 26, 2006- Photo of an anthelion and anthelic arcs display in Germany February 2006.
Atmospheric optical phenomena
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