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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 Angular diameter ： ウィキペディア英語版 Angular diameter The angular diameter or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view. In the vision sciences it is called the visual angle. The angular diameter can alternately be thought of as the angle through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side. ==Formula== The angular diameter of a circle whose plane is perpendicular to the displacement vector between the point of view and the centre of said circle can be calculated using the formula〔This can be derived using the formula for the length of a cord found at http://mathworld.wolfram.com/CircularSegment.html〕 :$\backslash delta\; =\; 2\backslash arctan\; \backslash left(\backslash frac\backslash right),$ in which $\backslash delta$ is the angular diameter, and $d$ and $D$ are the actual diameter of and the distance to the object. When $D\; \backslash gg\; d$, we have $\backslash delta\; \backslash approx\; d\; /\; D$, and the result obtained is in radians. For a spherical object whose ''actual'' diameter equals $d\_\backslash mathrm,$ and where $D$ is the distance to the ''centre'' of the sphere, the angular diameter can be found by the formula :$\backslash delta\; =\; 2\backslash arcsin\; \backslash left(\backslash frac\backslash right)$ The reason for the difference is that when looking at a sphere, the edges are the tangent points, which are closer to the observer than the centre of the sphere. For practical use, the distinction is only significant for spherical objects that are relatively close, since the small-angle approximation holds for $x\; \backslash ll\; 1$:〔http://www.mathstat.concordia.ca/faculty/rhall/mc/arctan.pdf〕 :$\backslash arcsin\; x\; \backslash approx\; \backslash arctan\; x\; \backslash approx\; x$ . 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「Angular diameter」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.