Nautical Dawn Time

The moment the Sun climbs to 12° below the horizon and the horizon line appears.

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Nautical dawn

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What is nautical dawn?

Nautical dawn is the start of morning nautical twilight: the moment the Sun's centre rises to 12° below the horizon. From then on the horizon can be made out at sea, so navigators can take star sights. It comes after astronomical dawn (−18°) and before civil dawn (−6°).

Phase	Sun below horizon	What you see
Civil twilight	0° to 6°	Enough light to work outdoors; brightest planets appear
Nautical twilight	6° to 12°	Horizon still visible at sea; bright stars visible
Astronomical twilight	12° to 18°	Sky looks dark to most people; faint glow remains
Night	more than 18°	No sunlight scattered in the sky

BMNT

In military planning, nautical dawn is called BMNT — “begin morning nautical twilight” — a standard reference time for dawn operations. Times are calculated in your browser from the Sun's position (the same method as NOAA-style solar calculators). They assume a flat horizon at sea level, so mountains, buildings and altitude can shift what you actually see by a few minutes.

Frequently asked questions

How long before sunrise is nautical dawn?

Roughly 50–80 minutes at mid-latitudes and about 45–50 minutes near the equator, more at high latitudes.

Is it light at nautical dawn?

Only faintly. The eastern sky begins to brighten and outlines are visible, but it is still too dark for most outdoor tasks.

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