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[[File:Complex halo display 01-03-09.jpg|300px|Complex halo display. Top to bottom: Supralateral arc, [[Parry arc]], [[Upper tangent arc]], [[22° halo]]. [[Sun dog]] to the right of the Sun.|thumb]]
[[File:Solar halos with foreground, Salem, MA, Oct 27, 2012.JPG|thumb|right|[[Circumzenithal arc]], Supralateral arc, [[Parry arc]], and [[Upper tangent arc]], in [[Salem, Massachusetts]], Oct 27, 2012.]]
In contrast to the static 46° halo, the shape of a supralateral arc varies with the elevation of the [[sun]]. Before the sun reaches 15°, the bases of the arc touches the [[lateral]] (oriented sidewise) sides of the 46° halo. As the sun rises from 15° to 27°, the supralateral arc almost overlap the 46° halo, why most reported observations of the latter most likely are observations of the former. As the sun goes from 27° to 32°, the apex of the arc touches the [[circumzenithal arc]] centred around [[zenith]] (as do the 46° halo when the sun is located between 15° and 27°). In addition, the supralateral arc is always located above the [[parhelic circle]] (below is the [[infraleteral arc]]) and is never perfectly circular.<ref name="meteoros">{{cite web▼
A '''supralateral arc''' is a comparatively rare member of the [[Halo (optical phenomenon)|halo]] family which in its complete form appears as a large, faintly rainbow-colored band in a wide arc above the sun and appearing to encircle it, at about twice the distance as the familiar [[22° halo]]. In reality, however, the supralateral arc does not form a circle and never reaches below the sun. When present, the supralateral arc touches the (much more common) [[circumzenithal arc]] from below. As in all colored halos, the arc has its red side directed towards the sun, its blue part away from it.
==Formation==
Supralateral arcs form when sun light enters horizontally oriented, rod-shaped [[hexagon]]al [[ice crystal]]s through a hexagonal base and exits through one of the [[prism (optics)|prism]] sides.
[[File:Icearcs1.jpg|thumb|A faint [[circumzenithal arc]] above an also faint supralateral arc]]
==Confusion with the 46° halo==
Due to its apparent circular shape and nearly identical location in the sky, the supralateral arc is often mistaken for the [[46° halo]], which does form a complete circle around the sun at approximately the same distance, but which is much rarer and fainter. Distinguishing between the two phenomena can be difficult, requiring the combination of several subtle indicators for proper identification.<ref>{{cite web|title=Is it a 46° halo or a supra/infralateral arc?|url=http://www.atoptics.co.uk/halo/46orsup.htm|publisher=www.atoptics.co.uk|accessdate=8 December 2015}}</ref>
▲In contrast to the static 46° halo, the shape of a supralateral arc varies with the elevation of the [[sun]]. Before the sun reaches 15°, the bases of the arc
| url = http://www.meteoros.de/arten/ee21e.htm
| title = Supralateral arc | publisher = Arbeitskreis Meteore e.V.
| accessdate = 2007-04-16 }} (Including a photo from January 1996, a 1980 computer simulation of a supralateral arc relative to a 46° halo, and a table pinning down differences between 46° halos and supralateral arcs.)</ref><ref name="paraselene">{{cite web▼
| url = http://www
▲}} (Including a photo from January 1996, a 1980 computer simulation of a supralateral arc relative to a 46° halo, and a table pinning down differences between 46° halos and supralateral arcs.)</ref><ref name="paraselene">{{cite web
▲ | url = http://www.engl.paraselene.de/html/supralateral_arcs.html
| title = Supralateral Arcs | publisher = www.paraselene.de
| accessdate =
Arguably the best way of distinguishing the halo from the arc is to carefully study the difference in colour and brightness. The 46° halo is six times fainter than the [[22° halo]] and generally white with a possible red inner edge. The supralateral arc, in contrast, can even be confused with the [[rainbow]] with clear blue and green strokes.<ref name="meteoros" />
== Gallery ==
▲Supralateral arcs form when sun light enters horizontally oriented, rod-shaped [[hexagon]]al [[ice crystal]]s through a hexagonal base and exits through one of the [[prism]] sides. Supra lateral arcs occur about once a year.<ref name="meteoros" />
<gallery>
Image:Supralateral_20jun09.jpg|Solar Halo, Upper Tangent Arc, Supralateral Arc : 20 June 2009 : Khonkaen, Thailand
File:Supralateral Arc.jpg|22° Halo, Upper Tangent Arc, Parry Arc, Supralateral Arc : May 2024 : Skagit Valley, Washington
</gallery>
== See also ==
* [[Infralateral arc]]
* [[Parry arc]]
* [[Lowitz arc]]
== References ==
{{reflist}}
== External links ==
* [http://www.atoptics.co.uk/halo/supinf.htm Atmospheric Optics - Supralateral & infralateral arcs] - including
* [http://www
* [http://www
{{DEFAULTSORT:Supralateral Arc}}
[[Category:Atmospheric optical phenomena]]
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