Editing Anticrepuscular rays

{{Short description|Meteorological optical phenomenon}}
[[File:Colorado_Anticrepuscular_Rays.jpg|thumb|Anticrepuscular rays toward the eastern horizon, as seen from Colorado at dusk]]
[[File:Anticrepuscular rays from above.jpg|thumb|right|These anticrepuscular rays appear to converge at the [[antisolar point]], as seen from an aircraft above the clouded ocean.]]
[[File:Crepuscular rays over Paranal Observatory, Chile.jpg|thumb|right|[[panoramic photography|Panoramic image]] showing both [[crepuscular rays|crepuscular]] and antisolar rays]]

'''Anticrepuscular rays''', or '''antisolar rays''',<ref>{{cite web
|url = http://www.atoptics.co.uk/atoptics/anti1.htm
|title = Anti-solar (anti-crepuscular) rays
|first = Les
|last = Cowley
|work = Atmospheric Optics
|accessdate = March 19, 2015
|mode = cs2
}}</ref> are [[meteorological optics| meteorological]] [[optical phenomenon|optical phenomena]] similar to [[crepuscular rays]], but appear opposite the [[Sun]] in the [[sky]]. Anticrepuscular rays are essentially [[parallel (geometry)|parallel]], but appear to converge toward the [[antisolar point]], the [[vanishing point]], due to a [[visual illusion]] from [[linear perspective]].<ref name="cresp">{{cite book
|pages=124–127
|url=https://books.google.com/books?id=0cpQGHqxQBUC&pg=PA124
|author=John A. Day
|title=The Book of Clouds
|year=2005
|publisher=Sterling Publishing Company, Inc.
|isbn=978-1-4027-2813-6
|mode = cs2
}}</ref><ref>{{cite web
|url = http://atoptics.co.uk/fz1113.htm
|title = Antisolar rays
|first = Les
|last = Cowley
|work = Atmospheric Optics
|accessdate = March 19, 2015
|mode = cs2
}}</ref>

Anticrepuscular rays are most frequently visible around [[dawn]] or [[dusk]]. This is because the atmospheric [[light scattering by particles|light scattering]] that makes them visible ([[backscatter]]ing) is larger for low angles to the horizon than most other angles. Anticrepuscular rays are dimmer than crepuscular rays because backscattering is less than [[forward scatter]]ing. 

Anticrepuscular rays can be continuous with crepuscular rays, curving across the whole sky in [[great circle]]s.<ref name="Lynch&1995">Lynch, D. K., & Livingston, W. (1995). Color and light in nature. Cambridge: Cambridge University Press.</ref>

==Mountain shadow==

A common example of a single anticrepuscular ray is provided by the shadow of a mountain at sunset, when viewed from the summit. It appears to be triangular, whatever the shape of the mountain, with the apex at the antisolar point.<ref name="Lynch&1995" />

==Wagon-wheel spokes==
[[File:Wagon wheel spoke rainbow with antisolar rays.jpg|thumb|A "wagon-wheel spokes" double rainbow with anti-crepuscular rays, Hurunui, New Zealand]]

Anticrepuscular rays are sometimes seen enclosed by a rainbow. In this case they can be called ''wagon-wheel spokes''.<ref name="Lynch&1995" />

==See also==
* [[Afterglow]]
* [[Earth's shadow]]

==References==
{{Reflist}}

==External links==
{{commonscat-inline}}
*[http://www.atoptics.co.uk/atoptics/anti1.htm Atmospheric optics: anticrepuscular rays]
*Images of anticrepuscular rays at [[Astronomy Picture of the Day]] site (copyrighted images):
**[http://antwrp.gsfc.nasa.gov/apod/ap081116.html Image of anticrepuscular rays in Colorado taken by John Britton]
**[http://antwrp.gsfc.nasa.gov/apod/ap060917.html A particularly vivid image taken by Daniel Herron of Woodstock, GA]

[[Category:Atmospheric optical phenomena]]


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