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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Parhelic circle ： ウィキペディア英語版 Parhelic circle 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.〔 (including an excellent HaloSim simulation of a parhelic circle.)〕 Parhelic circles form as beams of sunlight are 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 contributes to the parhelic circle near the sun, or internal (one or more reflections inside the crystal) which creates 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). Plate crystal displays The intensity distribution of the parhelic circle is largely dominated by 1-3-2 and 1-3-8-2 rays (cf. the nomenclature by W. Tape, i.e. 1 denotes the top hexagonal face, 2 the bottom face, and 3-8 enumerate the side faces in counter-clockwise fashion. A ray is notated by the sequence in which it encounters the prism faces). The former ray-path is responsible for the blue spot halo which occurs at an azimuth $\backslash theta\_\backslash mathfrak\}=2\backslash arcsin\backslash left(n\backslash cos\backslash left(\backslash arcsin\backslash left(1/n\backslash right)\backslash right)/\backslash cos\backslash left(e\backslash right)\backslash right)$, with $n$ being the material's index of refraction (not the Bravais index of refraction for inclined rays). However, many more features give a structure to the intensity pattern of the parhelic circle. Among the features of the parhelic circle are the Liljequist parhelia, the 90° parhelia (likely unobservable), the second order 90° parhelia (unobservable), the 22° parhelia and more. == See also == * Lower tangent arc * Upper tangent arc * Circumzenithal arc * Liljequist parhelion 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Parhelic circle」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.