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.
Even fractions of parhelic circles are less common than sun dogs and 22° halos. While parhelic circles are generally white in colour because they are produced by reflection, they can however show a bluish or greenish tone near the 120° parhelia and be reddish or deep violet along the fringes.
Parhelic circles form as beams of sunlight is reflected by vertical or almost vertical hexagonal ice crystals. The reflection can be either external (e.g. without the light passing through the crystal) which contribute to the parhelic circle near the sun, or internal (one or more reflections inside the crystal) which create much of the circle away from the sun. Because an increasing number of reflections makes refraction asymmetric some colour separation occurs away from the sun.
Sun dogs are always aligned to the parhelic circle (but not always to the 22° halo).
References
See also
External links
This article is licensed under the GNU Free Documentation License.
Last updated on Tuesday March 25, 2008 at 16:58:02 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation
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.
Even fractions of parhelic circles are less common than sun dogs and 22° halos. While parhelic circles are generally white in colour because they are produced by reflection, they can however show a bluish or greenish tone near the 120° parhelia and be reddish or deep violet along the fringes.
Parhelic circles form as beams of sunlight is reflected by vertical or almost vertical hexagonal ice crystals. The reflection can be either external (e.g. without the light passing through the crystal) which contribute to the parhelic circle near the sun, or internal (one or more reflections inside the crystal) which create much of the circle away from the sun. Because an increasing number of reflections makes refraction asymmetric some colour separation occurs away from the sun.
Sun dogs are always aligned to the parhelic circle (but not always to the 22° halo).
References
See also
External links
This article is licensed under the GNU Free Documentation License.
Last updated on Tuesday March 25, 2008 at 16:58:02 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation
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