1 sr on võrdne ruuminurgaga, mille tipp asub kera keskpunktis ja mis lõikab ära kera pinnal ala, mille pindala on võrdne kera raadiuse ruuduga.
SI unit of solid angle
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Symbol: sr
1 sr is equal to the solid angle that, having its vertex at the centre of a sphere, cuts off an area of the surface of the sphere equal to the square of the radius of the sphere.
