Definition

1. Noun:
   • The unit of solid angle adopted under the Systeme International d'Unites: A steradian is the standard unit for measuring solid angles in three-dimensional space. It is the three-dimensional analog of the radian for plane angles. One steradian is defined as the solid angle subtended at the center of a sphere by a portion of the sphere's surface having an area equal to the square of the sphere's radius.

Usage Examples

• Noun:
  • The total solid angle around a point is 4π steradians.
  • Luminous intensity is measured in candelas per steradian.
  • The concept of a steradian is fundamental in fields like radiometry and photometry.

Advanced Usage

• Mathematical Definition: If a surface area on a sphere of radius is equal to , then the solid angle Ω it subtends at the sphere's center is exactly 1 steradian (Ω = A / r²).
• Symbol: The steradian has the symbol sr.

Variants and Related Words

• Solid angle (n): The three-dimensional angle measured in steradians, which an object subtends at a point.
• Radian (n): The SI unit of plane angle, to which the steradian is the three-dimensional counterpart.

Synonyms

• Square radian: An alternative, descriptive name for the steradian, emphasizing its relationship to the radian.

Related Phrases and Contexts

• "Measured in steradians": A phrase used to specify the unit for a solid angle quantity.
  • The angular size of the light source is 0.5 steradians.
• "Per steradian": Commonly used in derived units to denote intensity per unit solid angle.
  • Radiance is measured in watts per steradian per square meter.

Noun

1. the unit of solid angle adopted under the Systeme International d'Unites