steradian: meaning, definition, pronunciation and examples
C2Technical/Scientific
Quick answer
What does “steradian” mean?
The SI unit of solid angle, defined as the solid angle at the centre of a sphere that subtends an area on its surface equal to the square of its radius.
Audio
Pronunciation
Definition
Meaning and Definition
The SI unit of solid angle, defined as the solid angle at the centre of a sphere that subtends an area on its surface equal to the square of its radius.
A three-dimensional angular measure in space, analogous to the radian for two-dimensional angles. It is used to quantify the spread of radiation, light flux, or other phenomena in three dimensions.
Dialectal Variation
British vs American Usage
Differences
No difference in meaning, spelling, or pronunciation. It is an international scientific term.
Connotations
None. Purely technical.
Frequency
Extremely low frequency in general discourse, used exclusively in technical fields in both regions with identical frequency.
Grammar
How to Use “steradian” in a Sentence
[Number] steradian(s)a solid angle of [X] steradians[Physical quantity] per steradianVocabulary
Collocations
Examples
Examples of “steradian” in a Sentence
verb
British English
- This concept cannot be verbed.
American English
- This concept cannot be verbed.
adverb
British English
- The light was measured steradianly. (Highly contrived, almost never used.)
American English
- The intensity was calculated steradianly. (Highly contrived, almost never used.)
adjective
British English
- The steradian measure is crucial for the calculation.
- The steradian value was recorded.
American English
- The steradian measurement is key for the model.
- The steradian coverage was insufficient.
Usage
Meaning in Context
Business
Virtually never used.
Academic
Used in advanced physics, engineering, astronomy, and photometry courses and publications.
Everyday
Never used.
Technical
Core term in radiometry, photometry, and antenna theory. Used to specify directional intensity of radiation or light.
Vocabulary
Synonyms of “steradian”
Neutral
Weak
Watch out
Common Mistakes When Using “steradian”
- Mispronouncing it as /ˈstɪərɪdɪən/ (like 'sterile').
- Using it to describe a flat, two-dimensional angle.
- Omitting the 's' in plural form when preceded by a number greater than one (e.g., '2 steradian' instead of '2 steradians').
FAQ
Frequently Asked Questions
There are exactly 4π (approximately 12.566) steradians in a sphere.
The symbol is 'sr'.
A radian measures a plane angle (2D), subtending an arc of a circle. A steradian measures a solid angle (3D), subtending an area on the surface of a sphere.
It is essential in photometry (measuring light), radiometry (measuring electromagnetic radiation), computer graphics (for lighting models), and antenna design (measuring signal directionality).
The SI unit of solid angle, defined as the solid angle at the centre of a sphere that subtends an area on its surface equal to the square of its radius.
Steradian is usually technical/scientific in register.
Steradian: in British English it is pronounced /ˌstɛˈreɪdɪən/, and in American English it is pronounced /stəˈreɪdiən/. Tap the audio buttons above to hear it.
Learning
Memory Aids
Mnemonic
Think of a STEreo speaker spreading sound in all directions. A STERadian measures how that sound spreads in 3D space, like an angle for a cone of sound.
Conceptual Metaphor
THE SOLID ANGLE IS A CONICAL VOLUME OF SPACE (extending the metaphor of a 2D angle 'sweeping out' an arc to a 3D angle 'sweeping out' an area on a sphere).
Practice
Quiz
What is the steradian a unit of?