Dictionary term
Astronomical Dusk
Direct answer
Astronomical Dusk is the evening instant when the Sun center descends to 18 degrees below the horizon.
Astronomical Dusk ends astronomical twilight at a -18-degree solar altitude.
Astronomical Dusk ends astronomical twilight at a -18-degree solar altitude.
A Sun–Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.Quick reference
- Use when
- Use Astronomical Dusk to plan dark-sky imaging, faint-object observing, and nightly almanac windows.
- Do not use it for
- Do not assume the sky will be dark at the threshold when Moon, aurora, smoke, or artificial light is present.
- Reference category
- Seasons & Earth Almanac
- Related terms
- Astronomical Dawn, Inferior Mirage, Astronomical Season, Equinox
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The story behind Astronomical Dusk
Observatory schedules adopted the standard as a practical approximation for when scattered sunlight becomes negligible.
Astronomical Dusk in spiritual tradition
Spiritually, Astronomical Dusk can open a period of attentive night observation grounded in actual sky conditions.
Astronomical Dusk: fact and faith, kept distinct
This is a factual calendar, astronomy, Earth-science, cultural-history, or observational reference. It can support wonder and practical planning without becoming a claim of fate, spiritual causation, or private revelation.
Astronomical Dusk in numerology
Astronomical Dusk 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 Dusk matters
It marks the conventional beginning of full natural night for many astronomical observations.
Astronomical Dusk at work: an example
At high summer latitudes Astronomical Dusk may not occur, leaving no formally defined astronomical night.
Where interpretation stops
Astronomical Dusk 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 - Official definitions used for sunrise, sunset, refraction, and twilight calculations.
- NOAA Global Monitoring Laboratory: Solar Calculator Glossary - NOAA definitions for solar geometry, atmospheric refraction, and civil, nautical, and astronomical twilight.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Also appears in
- Seasons & Earth Almanac
- Aliases
- None listed
- Last updated
- 2026-07-16
Begin the dark-sky window
Astronomical Dusk in a book is one thing; Astronomical Dusk in your own birth chart is your life. The Oracle casts your real chart and tells you what it means for your love, your work, and your year ahead, in conversation, free.
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More in Seasons & Earth Almanac
Common questions
What is Astronomical Dusk?
Astronomical Dusk is the evening instant when the Sun center descends to 18 degrees below the horizon.
How is Astronomical Dusk used in an almanac?
Use Astronomical Dusk to plan dark-sky imaging, faint-object observing, and nightly almanac windows.
What should I avoid when interpreting Astronomical Dusk?
Do not assume the sky will be dark at the threshold when Moon, aurora, smoke, or artificial light is present.
