astronomical twilight: meaning, definition, pronunciation and examples
LowTechnical/Scientific
Quick answer
What does “astronomical twilight” mean?
The period of twilight when the Sun is between 12 and 18 degrees below the horizon, during which the sky is very dark but not completely black, and faint stars become visible.
Audio
Pronunciation
Definition
Meaning and Definition
The period of twilight when the Sun is between 12 and 18 degrees below the horizon, during which the sky is very dark but not completely black, and faint stars become visible.
A technical term in astronomy and navigation; also used metaphorically to describe something extremely faint, dim, or occurring at the very edge of perception or possibility.
Dialectal Variation
British vs American Usage
Differences
No significant difference in meaning or usage. The term is identically defined and used in scientific contexts in both varieties.
Connotations
Purely technical/scientific in both regions.
Frequency
Equally low frequency in both UK and US English, confined to astronomy, aviation, navigation, and related technical fields.
Grammar
How to Use “astronomical twilight” in a Sentence
Astronomical twilight begins/ends when...During astronomical twilight, ...Observations were made in astronomical twilight.Vocabulary
Collocations
Examples
Examples of “astronomical twilight” in a Sentence
adjective
British English
- The astronomical twilight period is crucial for deep-sky observers.
American English
- We need the astronomical twilight data for the observation schedule.
Usage
Meaning in Context
Business
Virtually never used.
Academic
Used in astronomy, physics, atmospheric science, and navigation textbooks and papers.
Everyday
Extremely rare. Might be used by amateur astronomers or in specific outdoor contexts (e.g., photography).
Technical
Primary context. Used in astronomical almanacs, flight planning, naval navigation, and satellite operations.
Vocabulary
Synonyms of “astronomical twilight”
Neutral
Weak
Vocabulary
Antonyms of “astronomical twilight”
Watch out
Common Mistakes When Using “astronomical twilight”
- Using it interchangeably with 'dusk' or 'nightfall' in general conversation.
- Confusing it with 'nautical twilight' (Sun 6-12° below horizon).
- Misspelling as 'astronomic twilight' (though this is sometimes accepted).
FAQ
Frequently Asked Questions
Yes, the sky is very dark blue or black at the zenith, and the brightest stars and planets are clearly visible, but faint stars and deep-sky objects become easier to see as it progresses.
It varies greatly with latitude and season. At the equator, it lasts about 70 minutes. In mid-latitudes in summer, it can last all night (the Sun never gets more than 18° below the horizon).
Night. Astronomical twilight ends when the Sun is 18° below the horizon, which is the official definition of the beginning of night for astronomers.
Almost never. It is a precise scientific term. In everyday talk, people use 'dusk', 'nightfall', or simply 'dark'.
The period of twilight when the Sun is between 12 and 18 degrees below the horizon, during which the sky is very dark but not completely black, and faint stars become visible.
Astronomical twilight is usually technical/scientific in register.
Astronomical twilight: in British English it is pronounced /ˌæs.trəˈnɒm.ɪ.kəl ˈtwaɪ.laɪt/, and in American English it is pronounced /ˌæs.trəˈnɑː.mɪ.kəl ˈtwaɪ.laɪt/. Tap the audio buttons above to hear it.
Learning
Memory Aids
Mnemonic
Think: 'ASTROnomers need it to be ASTROnomically dark to see the stars.' The 'astronomical' part directly links to the science of astronomy.
Conceptual Metaphor
THE EDGE OF NIGHT (a precise, measurable boundary between day and night); EXTREME DIMNESS (used metaphorically for very faint chances or perceptions).
Practice
Quiz
What defines the beginning of astronomical twilight?