Seasons and sky
Nautical Dawn
Direct answer
Nautical Dawn is the morning instant when the Sun center rises through 12 degrees below the horizon.
Nautical Dawn begins nautical twilight at a -12-degree solar altitude.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Civil Dusk, Nautical Dusk, Astronomical Season, Equinox
Nautical Dawn begins 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 Dawn
Nautical almanacs published this threshold to help mariners time star observations around first horizon visibility.
Why Nautical Dawn matters
Nautical Dawn marks the start of a traditional navigation interval when horizon and bright stars may become jointly usable.
Nautical Dawn in practice: an example
Nautical Dawn follows astronomical dawn and precedes Civil Dawn.
Where readings of Nautical Dawn go wrong
It is a mistake to rely on the threshold alone for safe navigation; verify weather, horizon, equipment, and current official guidance.
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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More in Seasons & Earth Almanac
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Common questions
What is Nautical Dawn?
Nautical Dawn is the morning instant when the Sun center rises through 12 degrees below the horizon.
What do people get wrong about Nautical Dawn?
It is a mistake to rely on the threshold alone for safe navigation; verify weather, horizon, equipment, and current official guidance.
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