An infralateral arc (or lower lateral tangent arc) is a rare
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 ...
, 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 wit ...
appearing similar to a
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 ...
under a white
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. ...
. Together with the
supralateral arc they are always located outside the seldom observable
46° halo
A 46° halo is a rare atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 46° around the Sun. At solar elevations of 15–27°, 46° halos are often confused with the less rare and more colourful su ...
, but in contrast to supralateral arcs, infralateral arcs are always located below the parhelic circle.
The shape of an infralateral arc varies with the elevation of 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 ...
. Between sunrise and before the observed Sun reaches about 50° over Earth's horizon, two infralateral arcs are located on either side (e.g.
lateral
Lateral is a geometric term of location which may refer to:
Healthcare
*Lateral (anatomy), an anatomical direction
* Lateral cricoarytenoid muscle
* Lateral release (surgery), a surgical procedure on the side of a kneecap
Phonetics
*Lateral co ...
) of the 46° halo, their convex apexes lying
tangent
In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. More ...
to the 46° halo. As the observed Sun reaches above 68° the two arcs unite to a single concave arc tangent to the 46° halo vertically under the Sun.
[ (Including a photo from January 1996 and a 1980 computer simulation of infra- and supralateral arcs relative to a 46° halo.)]
Infralateral arcs form when sunlight enters horizontally oriented, rod-shaped
hexagon
In geometry, a hexagon (from Ancient Greek, Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple polygon, simple (non-self-intersecting) hexagon is 720°.
Regular hexa ...
al
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 through a hexagonal base and exits through one of the
prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
sides. Infralateral arcs occur about once a year.
They are often observed together with
circumscribed halo
In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius.
Not every polyg ...
s and
upper tangent arc
Tangent arcs are a type of halo, an atmospheric optical phenomenon, which appears above and below the observed Sun or Moon, tangent to the 22° halo. To produce these arcs, rod-shaped hexagonal ice crystals need to have their long axis aligned ...
s.
See also
*
Circumzenithal arc
*
Tangent arc
Tangent arcs are a type of halo, an atmospheric optical phenomenon, which appears above and below the observed Sun or Moon, tangent to the 22° halo. To produce these arcs, rod-shaped hexagonal ice crystals need to have their long axis aligned h ...
*
Parry arc
A Parry arc is a rare halo, an optical phenomenon which occasionally appears over a 22° halo together with an upper tangent arc.
Discovery
The halo was first described by Sir William Edward Parry (1790–1855) in 1820 during one of his Arct ...
References
External links
Atmospheric Optics - Supralateral & infralateral arcs- including
HaloSim computer simulations and crystal illustrations.
Atmospheric optical phenomena
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