Nautical Twilight
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Sun crosses 12° below horizon
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Sun crosses 12° below horizon
Current Local Time
—This nautical twilight calculator shows the exact nautical dawn and nautical dusk times (sun 6°–12° below horizon) for any location.
What Is Nautical Twilight?
Nautical twilight spans the period when the sun sits between 6 and 12 degrees below the horizon. The sky is dark enough for bright stars to appear, yet the horizon remains just visible enough for mariners to take celestial sights. Named for its critical role in maritime navigation, nautical twilight allowed sailors to calibrate their compasses by sighting both stars and the horizon line simultaneously.
The boundary between nautical and civil twilight is defined by visibility: during nautical twilight, the sea horizon is no longer clearly visible for navigation purposes. This is why the phase is named after nautical use — it marks the cutoff where sailors can no longer reliably use the horizon reference for celestial navigation. For photographers and stargazers, nautical twilight represents the transition from usable ambient light to the beginning of true darkness.
How Our Nautical Twilight Calculator Works
Our nautical twilight calculator computes the exact times when the sun reaches 6 degrees and 12 degrees of depression below the horizon, defining the start and end of nautical dawn and nautical dusk. It uses the SunCalc library with standard atmospheric refraction of 0.833° applied, and runs entirely in your browser.
Using your geographic coordinates and date, the tool applies the USNO solar algorithm with refraction corrections to deliver precise nautical twilight boundaries for planning and navigation purposes. No data is sent to any server — the entire computation is local and instant.
FAQ — Nautical Twilight
When does nautical twilight begin in the morning?
Nautical dawn begins when the sun reaches 6° below the horizon, typically 30-50 minutes before sunrise. It ends when the sun reaches 0° (civil dawn). In my experience, the most productive window for astrophotography wind-down is during nautical twilight — there's still enough darkness for star photography but you can begin seeing your equipment.
Is nautical twilight the same as blue hour?
They overlap significantly but aren't identical. Blue hour (4°-8° below horizon) falls mostly within nautical twilight (6°-12° below). The first half of blue hour coincides with late civil twilight, while the second half overlaps with early nautical twilight. Blue hour is the photographically most dramatic portion of the twilight sequence.
Why is it called nautical twilight?
Because sailors historically used this period for celestial navigation — the horizon was still visible enough to take accurate star sights, but stars were bright enough to identify. The term dates back centuries and reflects the practical importance of this twilight phase for maritime safety. Modern aviation authorities still use nautical twilight to define VFR flight rules.
How long does nautical twilight last?
Nautical twilight typically lasts 30-50 minutes at most latitudes, but near the poles it can last much longer — or not occur at all during summer when the sun never drops below 12°. Near the equator, it's shorter because the sun descends steeply. Use the calculator above for exact durations at your location.
What can I see during nautical twilight?
During nautical twilight, you can see bright stars, planets, and the brighter constellations. The horizon is still faintly visible, especially over water. Mercury and Venus are often visible near the horizon. I've found it's the ideal time to watch for the ISS (International Space Station) passes — the sky is dark enough to see it but light enough to orient yourself.