arc second: meaning, definition, pronunciation and examples
LowTechnical / Scientific
Quick answer
What does “arc second” mean?
A unit of angular measurement equal to 1/3600th of a degree, used primarily in astronomy, geography, and surveying.
Audio
Pronunciation
Definition
Meaning and Definition
A unit of angular measurement equal to 1/3600th of a degree, used primarily in astronomy, geography, and surveying.
A minute subdivision of angular distance representing extreme precision, symbolised by ". The term is also conceptually used metaphorically to denote an extremely small measure or increment.
Dialectal Variation
British vs American Usage
Differences
Usage is identical. The term is purely technical and standardised across English-speaking scientific communities.
Connotations
None. Purely denotative and technical.
Frequency
Equally rare outside technical fields in both regions.
Grammar
How to Use “arc second” in a Sentence
The [object] has a parallax of [number] arc seconds.Measure the angle to an accuracy of [number] arc seconds.Vocabulary
Collocations
Examples
Examples of “arc second” in a Sentence
adjective
British English
- The arc-second measurement was crucial for the survey.
American English
- The arc-second precision of the instrument is state-of-the-art.
Usage
Meaning in Context
Business
Virtually never used.
Academic
Exclusively used in technical papers within astronomy, astrophysics, geomatics, and related fields.
Everyday
Never used in everyday conversation.
Technical
The primary domain of use. Essential for describing angular resolution, parallax, astrometric precision, and coordinate accuracy.
Vocabulary
Synonyms of “arc second”
Neutral
Weak
Vocabulary
Antonyms of “arc second”
Watch out
Common Mistakes When Using “arc second”
- Pronouncing it as 'ark second' (like Noah's Ark) instead of 'arc' /ɑːk/ or /ɑːrk/.
- Confusing it with a unit of time.
- Writing it as 'arcsecond' (while sometimes accepted, the spaced form 'arc second' is more standard).
FAQ
Frequently Asked Questions
No, it is a unit of angular measurement, not time. The similarity in name is historical, stemming from the sexagesimal (base-60) system used for both time and angles.
The symbol is a double prime mark ("). For example, 15 arc seconds is written as 15".
There are 60 arc seconds in one arc minute, just as there are 60 seconds in a minute of time.
An arc second is an extremely small angle. It is roughly the angle subtended by a pound coin (≈2.3cm) viewed from a distance of about 4.8 kilometres.
A unit of angular measurement equal to 1/3600th of a degree, used primarily in astronomy, geography, and surveying.
Arc second is usually technical / scientific in register.
Arc second: in British English it is pronounced /ˈɑːk ˌsɛk.ənd/, and in American English it is pronounced /ˈɑːrk ˌsɛk.ənd/. Tap the audio buttons above to hear it.
Learning
Memory Aids
Mnemonic
Think of slicing a single degree of a pie into 3600 tiny slivers; one sliver is an arc second.
Conceptual Metaphor
EXTREME PRECISION IS SUBDIVIDING A CIRCLE (The metaphor is inherent in the term's definition of minute angular division).
Practice
Quiz
In which field is the term 'arc second' most commonly used?