Dictionary term
Astronomical Twilight
Direct answer
Astronomical Twilight is the interval when the Sun is between 12 and 18 degrees below the horizon; beyond it, the sky is conventionally considered fully dark for astronomy.
Astronomical Twilight occurs while the Sun is 12 to 18 degrees below the horizon.
Astronomical Twilight occurs while the Sun is 12 to 18 degrees below the horizon.
A scientific orientation to scale, light, or motion; the article supplies the precise definition.Quick reference
- Use when
- Use Astronomical Twilight with a date and location because its duration changes by latitude and season and may not occur at high latitudes in summer.
- Do not use it for
- Do not describe twilight boundaries as abrupt physical switches; they are practical conventions applied to a gradual change.
- Reference category
- Astronomy & Skywatching
- Related terms
- Astronomy, Skywatching, Celestial Sphere, Ecliptic
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The story behind Astronomical Twilight
Civil, nautical, and astronomical twilight conventions divide the gradual transition between daylight and night by solar depression angle.
Astronomical Twilight in spiritual tradition
Twilight honors thresholds and teaches patience with transitions that do not happen all at once.
Astronomical Twilight: fact and faith, kept distinct
This is a factual astronomy, calendar, Earth-science, cultural, or historical reference. It can support wonder at the created order without becoming a claim of fate, worship, or private revelation.
Astronomical Twilight in numerology
Astronomical Twilight is not a numerology claim. Any numbers attached to it should retain their ordinary scientific, calendrical, navigational, or historical meaning unless a separate symbolic interpretation is clearly labeled.
Why Astronomical Twilight matters
The term gives observers a more useful darkness threshold than sunset alone, especially for faint stars, galaxies, and meteor watching.
Astronomical Twilight at work: an example
A deep-sky session may begin after evening astronomical twilight ends rather than immediately at sunset.
Where interpretation stops
Astronomical Twilight is presented as sourced astronomy, calendrical, Earth-science, cultural, or instrument-history reference. Definitions should distinguish measured phenomena from civil convention and historical interpretation, preserve location and time dependencies, and avoid turning factual sky data into a deterministic personal claim.
Sources and editorial method
Research references used for this entry include:
- U.S. Naval Observatory: Rise, Set, and Twilight Definitions - Definitions used by USNO for sunrise, sunset, moonrise, moonset, and twilight.
- U.S. Naval Observatory: Astronomical Information Center - Official index for time, calendars, seasons, coordinates, and observable sky phenomena.
- Source
- The Great Almanac Dictionary
- Category
- Astronomy & Skywatching
- Also appears in
- Astronomy & Skywatching
- Aliases
- None listed
- Last updated
- 2026-07-15
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Common questions
What is Astronomical Twilight?
Astronomical Twilight is the interval when the Sun is between 12 and 18 degrees below the horizon; beyond it, the sky is conventionally considered fully dark for astronomy.
How is Astronomical Twilight used in an almanac?
Use Astronomical Twilight with a date and location because its duration changes by latitude and season and may not occur at high latitudes in summer.
What should I avoid when interpreting Astronomical Twilight?
Do not describe twilight boundaries as abrupt physical switches; they are practical conventions applied to a gradual change.
