This number represents the extent of the figure D as seen from a point O in space, and is usually expressed in steradians. Steradians are a supplementary unit of the International System of Units, and their symbol is sr. A cone is formed by the complete half line that passes through point D, with O as its end. This is the solid angle, and its size is measured by the area of the part on the sphere when it is cut with a sphere of radius 1 centered at O. In particular, the solid angle of the entire space as seen from O is 4πsr, and the solid angle of the half space is 2πsr. [Minoru Kurita] Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend |
空間で一点Oから図形Dを見る広がりを表す数で、普通ステラジアンsteradian単位で表す。なお、ステラジアンは国際単位系の補助単位で、記号はsr。Oを端としてDの点を通る半直線全体でできる錐(すい)をつくる。これが立体角で、その大きさは、これをOを中心とする半径1の球面で切るとき、球面上にできる部分の面積で計る。とくに、Oから見た全空間の立体角は4πsrであり、半空間の立体角は2πsrである。 [栗田 稔] 出典 小学館 日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について 情報 | 凡例 |
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