Seasons and sky
Nautical Twilight
Direct answer
Nautical Twilight is the interval when the Sun center lies between 6 and 12 degrees below the horizon.
Nautical Twilight spans Sun altitudes from -6 to -12 degrees.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Civil Twilight, Blue Hour, Astronomical Season, Equinox
Nautical Twilight spans Sun altitudes from -6 to -12 degrees.
A Sun-Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.
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The story behind Nautical Twilight
Mariners relied on the twilight overlap between a visible sea horizon and navigational stars for sextant sights.
Why Nautical Twilight matters
During favorable conditions the horizon and brighter stars can both be visible, historically supporting celestial navigation.
How to read Nautical Twilight
Nautical Twilight speaks to navigation planning, marine operations, and observing the transition from bright to dark sky.
Nautical Twilight in practice: an example
Morning Nautical Twilight ends at civil dawn when the Sun rises past 6 degrees below the horizon.
Where readings of Nautical Twilight go wrong
It is a mistake to assume the sea horizon or stars will be visible through fog, cloud, glare, or heavy light pollution.
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 Twilight?
Nautical Twilight is the interval when the Sun center lies between 6 and 12 degrees below the horizon.
What do people get wrong about Nautical Twilight?
It is a mistake to assume the sea horizon or stars will be visible through fog, cloud, glare, or heavy light pollution.
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