Sunrise, sunset & twilight calculator

Daily sun and twilight times for any position. Useful for:

• Switching navigation lights at sunset under COLREG Rule 20.
• Bridge watch handover at first/last light.
• Celestial fix planning — nautical twilight is the window when both stars and the horizon are visible.
• Cargo operations scheduling at ports with daylight-only restrictions.
• Polar voyage planning — periods of polar day or polar night.

Twilight definitions

• Civil twilight — sun centre 6° below horizon. Brightest navigation aids visible; outdoor activities possible without artificial light.
• Nautical twilight — sun 12° below. Horizon still visible against a dark sky; the window for celestial sights with sextant.
• Astronomical twilight — sun 18° below. End of last residual sky brightness; a fully dark sky for astronomy.
• Sunrise / sunset — upper limb of the sun on the horizon, corrected for atmospheric refraction (-0.833°).

See also

• · Navigation lights — Rule 20 timing requirements.
• · UTC ↔ local converter — port-by-port DST aware.
• · Distance & bearing — passage planning.

Last updated 2026-04-27