A Liljequist parhelion is a rare
halo
HALO, halo, halos or haloes may refer to:
Most common meanings
* Halo (optical phenomenon)
* Halo (religious iconography), a ring of light around the image of a head
* ''Halo'' (franchise), a sci-fi video game series (2001–2021)
Arts and en ...
, an
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 with ...
in the form of a brightened spot 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 secti ...
approximately 150–160° from the
sun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
; i.e., between the position of the
120° parhelion
A 120° parhelion (plural: 120° parhelia) is a relatively rare halo, an optical phenomenon occasionally appearing along with very bright sun dogs (also called parhelia) when ice crystal-saturated cirrus clouds fill the atmosphere. The 120° parhe ...
and the
anthelion
An anthelion (plural anthelia, from late Greek language, Greek ανθηλιος, "opposite the sun") is a rare optical phenomenon of the Halo (optical phenomenon), halo family. It appears on the parhelic circle opposite to the Sun as a faint whi ...
.
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.
.
The phenomenon was first observed by
Gösta Hjalmar Liljequist
Gösta Hjalmar Liljequist (1914–1995) was a Swedish meteorologist.
In Sweden, radio broadcast weather forecasts begun in 1926, and, starting in 1941, Liljequist was one of the recurrent meteorologists appearing in Swedish radio for many years ...
in 1951 at
Maudheim,
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
during the
Norwegian–British–Swedish Antarctic Expedition
The Norwegian–British–Swedish Antarctic Expedition (also known as NBSX or NBSAE) (1949–1952) was the first Antarctica expedition involving an international team of scientists. The team members came from Norway, Sweden and the British Commonw ...
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.
A theoretical and experimental investigation
of the Liljequist parhelion caused by perfect hexagonal plate crystals showed that the azimuthal position of maximum intensity occurs at
,
where the refractive index
to use for the angle
of total internal reflection is Bravais' index for inclined rays, i.e.
for a solar elevation
. For ice at zero solar elevation this angle is
. The dispersion of ice causes a variation of this angle, leading to a blueish/cyan coloring close to this azimuthal coordinate. The halo ends towards the anthelion at an angle
.
See also
*
Sun dog
A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in atmospheric science, 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 ...
References
External links
A fish eye photo by Günter Röttler, Hagen, September 1983featuring a parhelic circle with a 120° parhelion and a Liljequist parhelion.
List of observations(pick Liljequist parhelia as a halo filter.)
Atmospheric optical phenomena
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