Tides / Guides / Nautical twilight
Nautical twilight
Updated October 15, 2026.
Nautical twilight sits between first light and dawn in the morning, and between dusk and last light in the evening. The sun is 12 degrees below the horizon at the start of the morning window and at the end of the evening window. Sailors named it for the horizon: this is when the line of the sea can be told from the sky, which is what a sextant needs, while the brighter stars are still visible.
On the station page the morning time is "Nautical twilight begins" and the evening time is "Nautical twilight ends." The begins time is after first light and before dawn. The ends time is after dusk and before last light. The stretch in between is not daylight. It is the long middle of the day plus both twilights, so the two clock times should be read as a start and a finish, not as a short window like golden hour.
What you can see
In the morning the sky goes from mostly dark at first light to a visible horizon at nautical twilight, then to a clearly lit landscape at dawn. Artificial light still matters. A marina lamp will hide the horizon that a dark beach shows. In the evening the same steps run backward after sunset: dusk, then the nautical end, then last light.
The times are for the station coordinate, in local time at the station. A headland a few miles east sees them a little earlier. The page does not adjust for a hill or a city skyline blocking the horizon.