astronomical unit: meaning, definition, pronunciation and examples
C1+Formal, Scientific
Quick answer
What does “astronomical unit” mean?
A standard unit of measurement in astronomy, equal to the average distance from the Earth to the Sun, approximately 149.
Audio
Pronunciation
Definition
Meaning and Definition
A standard unit of measurement in astronomy, equal to the average distance from the Earth to the Sun, approximately 149.6 million kilometres (93 million miles).
Figuratively, used to describe an extremely large quantity, measurement, or difference.
Dialectal Variation
British vs American Usage
Differences
No difference in meaning or usage. Spelling conventions follow regional norms for 'metre'/'meter' and 'kilometre'/'kilometer' when writing out the equivalent distance.
Connotations
Identical technical meaning. The figurative use is equally understood.
Frequency
Equally common in scientific/educational contexts in both regions. Figurative use is slightly more frequent in UK media.
Grammar
How to Use “astronomical unit” in a Sentence
[Subject] is/measures X astronomical units (from Y).The distance was given in astronomical units.It's astronomical units away.Vocabulary
Collocations
Examples
Examples of “astronomical unit” in a Sentence
verb
British English
- The probe will have to astronomical-unit its way across the inner system.
- (Note: Not standard; no genuine verb use exists)
American English
- We need to AU that distance for the model.
- (Note: Informal/technical slang as a verb)
adverb
British English
- The comet passed astronomically-unit close. (Non-standard)
American English
- They measured it astronomically-unit by unit. (Non-standard)
adjective
British English
- The astronomical-unit measurement is fundamental.
- It's an astronomical-unit distance.
American English
- The astronomical-unit value is precise.
- We took AU measurements.
Usage
Meaning in Context
Business
Rare, except in hyperbolic figurative use: 'The cost overrun was astronomical.'
Academic
Core term in astronomy, astrophysics, and planetary science courses and literature.
Everyday
Virtually never used in literal sense. Figurative use possible but uncommon.
Technical
The standard unit for expressing distances within the solar system and between stars in nearby systems.
Vocabulary
Synonyms of “astronomical unit”
Strong
Neutral
Weak
Vocabulary
Antonyms of “astronomical unit”
Watch out
Common Mistakes When Using “astronomical unit”
- Using 'astrological unit' (incorrect).
- Confusing it with a 'light-year'. An AU is much smaller (~8.3 light-minutes).
- Using plural 'astronometrics units' (non-existent word).
FAQ
Frequently Asked Questions
Yes, 'AU' is the standard international abbreviation for Astronomical Unit in scientific literature.
Figuratively, yes (e.g., 'an astronomical unit of debt'), but it's less common than simply using 'astronomical'. It's a creative extension.
One astronomical unit is defined as exactly 149,597,870.7 kilometres.
Rarely. For distances between stars, light-years or parsecs are more practical, as AUs would result in impractically large numbers.
A standard unit of measurement in astronomy, equal to the average distance from the Earth to the Sun, approximately 149.
Astronomical unit is usually formal, scientific in register.
Astronomical unit: in British English it is pronounced /ˌæs.trəˈnɒm.ɪ.kəl ˈjuː.nɪt/, and in American English it is pronounced /ˌæs.trəˈnɑː.mɪ.kəl ˈjuː.nɪt/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “Not even one astronomical unit away would be far enough!”
- “He's an astronomical unit out of his depth.”
Learning
Memory Aids
Mnemonic
Imagine the Sun and Earth connected by a ruler exactly 149.6 million km long — that's your A-stronomical Unit.
Conceptual Metaphor
A UNIT OF MEASUREMENT IS A RULER (for the cosmos). LARGENESS IS ASTRONOMICAL.
Practice
Quiz
What is the primary purpose of the astronomical unit?