Twilight Duration

MARITIME – CELETIAL NAVIGATION CALCULATOR Twilight Duration A precise tool.
πŸ“–
What is the Twilight Duration & How does it work?
Twilight is defined by the Sun’s geometric depression angle below the horizon. Civil twilight ends when the Sun reaches –6Β°, nautical twilight at –12Β°, and astronomical twilight at –18Β°. These limits are important for navigation because they determine when the horizon is visible enough for sight reduction and when stars become usable for celestial fixes. The duration of each twilight period depends primarily on the observer’s latitude (Ο†) and the Sun’s declination (Ξ΄) for the given date. Using spherical astronomy, the hour angle (H) at which the Sun reaches a specific depression angle (hβ‚€) is found from the cosine formula. The total time the Sun spends between two depression angles is twice the hour angle, converted to hours (the Earth rotates 15Β° per hour). For practical navigation, the twilight duration can be calculated with a simple algorithm: determine the day‑of‑year, compute the Sun’s declination, then apply the hour‑angle equation for hβ‚€ = –6Β°, –12Β°, and –18Β°. The result tells a mariner how long the sky will be usable for visual navigation or star sightings on any given night.
cos H = frac{sin h_0 – sin phi sin delta}{cos phi cos delta}
H = hour angle at twilight limit (radians), hβ‚€ = Sun’s depression angle (–6Β°, –12Β°, –18Β°), Ο† = observer latitude, Ξ΄ = Sun declination
βš™οΈ
Parameters
Result β€”
❓
Frequently Asked Questions
What is civil twilight?
Civil twilight ends when the Sun reaches –6Β° below the horizon, marking the end of sufficient light for general outdoor activities.
How does latitude affect twilight duration?
Higher latitudes experience longer twilight periods compared to lower latitudes due to the angle at which the Earth rotates.
What is the significance of nautical twilight in navigation?
Nautical twilight, when the Sun reaches –12Β° below the horizon, indicates that the horizon is no longer visible and stars are becoming usable for celestial navigation.
How do I calculate twilight duration for a specific location?
Input your latitude and the date into the calculator to determine the duration of civil, nautical, and astronomical twilight.
What is the difference between civil and nautical twilight?
Civil twilight ends at –6Β° while nautical twilight begins at –12Β°, with nautical twilight being darker and more suitable for star navigation.
Can I use this calculator for any location on Earth?
Yes, as long as you provide the correct latitude and date, the calculator will give accurate twilight durations for any location on Earth.
Why is astronomical twilight important in maritime navigation?
Astronomical twilight, when the Sun reaches –18Β° below the horizon, marks the end of twilight and the beginning of darkness, crucial for celestial observations.

Results are for informational purposes only and do not constitute professional advice.