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
Optical phenomena are any observable events that result from the interaction of light and matter.
All optical phenomena coincide with quantum phenomena. Common optical phenomena are often due to the interaction of light from the sun or moon wit ...
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'' (franch ...
family. It appears on the
parhelic circle
A parhelic circle is a type of halo, an optical phenomenon appearing as a horizontal white line on the same altitude as the sun, or occasionally the Moon. If complete, it stretches all around the sky, but more commonly it only appears in sections. ...
opposite to the
sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
as a faint white spot, not unlike a
sundog
A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° h ...
, 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 crystal
Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust.
Formation
The hugely symmetric shapes are due to depositional growth, na ...
s 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 arc
Wegener may refer to:
Astronomy
* 29227 Wegener, a main-belt asteroid
* Wegener (lunar crater)
* Wegener (Martian crater)
Places
* Wegener Range, an Antarctic mountain range
* Mount Wegener, an Antarctic mountain in the Read Mountains in the ...
s occasionally cross the sky to converge in the anthelion.
[ (including fish eye photo a.o.)]
See also
*
Anthelic point
The antisolar point is the abstract point on the celestial sphere directly opposite the Sun from an observer's perspective. This means that the antisolar point lies above the horizon when the Sun is below it, and vice versa. On a sunny day, t ...
*
False sunrise
A false sunrise is any of several atmospheric optical phenomena in which the Sun appears to have risen, but is actually still some distance below the horizon. A number of different atmospheric conditions can be responsible for this effect, all ...
*
Glory
*
Liljequist parhelion
A Liljequist parhelion is a rare Halo (optical phenomenon), 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 anthel ...
*
Optical phenomenon
Optical phenomena are any observable events that result from the interaction of light and matter.
All optical phenomena coincide with quantum phenomena. Common optical phenomena are often due to the interaction of light from the sun or moon wit ...
*
Parhelion
A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° h ...
*
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 c ...
*
Subparhelic circle
The subparhelic circle is a rare halo, an optical phenomenon, located below the horizon. It passes through both the subsun (below the Sun) and the antisolar point (opposite to the Sun). The subparhelic circle is the subhorizon counterpart to the ...
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
{{climate-stub