Seasons and sky
Nautical Dusk
Direct answer
Nautical Dusk is the evening instant when the Sun center reaches 12 degrees below the horizon.
Nautical Dusk ends nautical twilight at a -12-degree solar altitude.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Nautical Dawn, Astronomical Dawn, Astronomical Season, Equinox
Nautical Dusk ends nautical twilight at a -12-degree solar altitude.
A Sun-Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.
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The story behind Nautical Dusk
Sextant practice made evening nautical twilight a valuable period for obtaining multiple star sights.
Why Nautical Dusk matters
Nautical Dusk marks the end of the classic evening period when horizon and navigational stars may both be discernible.
How to read Nautical Dusk
Nautical Dusk speaks to marine observing, twilight photography, and the transition into darker sky.
Nautical Dusk in practice: an example
After Nautical Dusk, the horizon usually becomes harder to distinguish even as more stars emerge.
Where readings of Nautical Dusk go wrong
Local haze and sea state can erase the horizon well before the calculated threshold.
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
- Last updated
- 2026-09-26
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Common questions
What is Nautical Dusk?
Nautical Dusk is the evening instant when the Sun center reaches 12 degrees below the horizon.
What do people get wrong about Nautical Dusk?
Local haze and sea state can erase the horizon well before the calculated threshold.
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