Anthelion
Encyclopedia
An anthelion 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.
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 reflection 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 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.
Optical phenomenon
An optical phenomenon is any observable event that results from the interaction of light and matter. See also list of optical topics and optics. A mirage is an example of an optical phenomenon....
appearing on the parhelic circle
Parhelic circle
A parhelic circle is a 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
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
as a faint white halo
Halo (optical phenomenon)
A halo from Greek ἅλως; also known as a nimbus, icebow or gloriole) is an optical phenomenon produced by ice crystals creating colored or white arcs and spots in the sky. Many are near the sun or moon but others are elsewhere and even in the opposite part of the sky...
, not unlike a sundog
Sun dog
A sun dog or sundog, scientific name parhelion ; , also called a mock sun or a phantom sun, is an atmospheric phenomenon that creates bright spots of light in the sky, often on a luminous ring or halo on either side of the sun.Sundogs may appear as a colored patch of light to the left or right of...
.
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 reflection 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
120° parhelion
A 120° parhelion is a relatively rare halo, an optical phenomenon occasionally appearing along with very bright sun dogs as ice crystal-saturated cirrus clouds fill the atmosphere...
(and two Liljequist parhelia
Liljequist parhelion
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 ....
) caused by plate crystals. The Tricker and diffuse arcs are produced in singly oriented column crystals and form a Ankh
Ankh
The ankh , also known as key of life, the key of the Nile or crux ansata, was the ancient Egyptian hieroglyphic character that read "eternal life", a triliteral sign for the consonants ʻ-n-ḫ...
-like shape passing through the anthelion. Wegener arcs occasionally crosses the sky to converge in the anthelion.
See also
- Antisolar pointAntisolar pointThe antisolar point is the imaginary point on the celestial sphere exactly opposite the Sun. It is where anticrepuscular rays appear to converge, and on a moonless night away from city lights, it is often possible to see the gegenschein there. The apex of a rainbow will also form roughly 42...
- False sunriseFalse sunriseA false sunrise or dawn sundog is a very particular kind of parhelion, belonging to the optical phenomenon family of halos.It is an atmospheric optical phenomenon associated with the reflection or refraction of sunlight by small ice crystals making up cirrus or cirrostratus clouds in the very...
- GloryGlory (optical phenomenon)A glory is an optical phenomenon that resembles an iconic saint's halo about the shadow of the observer's head. The effect is produced by light backscattered towards its source by a cloud of uniformly sized water droplets...
- Liljequist parhelionLiljequist parhelionA 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 ....
- Optical phenomenonOptical phenomenonAn optical phenomenon is any observable event that results from the interaction of light and matter. See also list of optical topics and optics. A mirage is an example of an optical phenomenon....
- Parhelion
- RainbowRainbowA rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc...
- Subparhelic circleSubparhelic circleThe 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...
External links
- Earth Science Picture of the Day, April 26, 2006 - Photo of an anthelion and anthelic arcs display in Germany February 2006.