Understanding the Difference Between Nautical, Astronomical, and Civil Twilight

This illustration explains the different phases of twilight and nighttime based on the sun's position relative to the horizon: Day/Sunrise/Sunset, Civil Twilight, Nautical Twilight, Astronomical Twilight, and Nighttime, with corresponding sun angles from above to more than 18 degrees below the horizon.

By Dr. Bryan Rithesh Miranda

Twilight is a fascinating period between day and night when the sun is just below the horizon. However, did you know there are three types of twilight—civil, nautical, and astronomical—each serving distinct purposes? This article explains their differences and how they are used in everyday life.

What Is Twilight?

Twilight occurs when sunlight scatters in the atmosphere, softening the boundary between day and night. It is divided into three phases based on the sun's angle below the horizon.

1. Civil Twilight

• This phase happens when the sun is 0° to 6° below the horizon.

• The sky remains bright enough to perform outdoor activities without artificial lighting.

• Ideal for outdoor photography, as the light is soft and even.

• Civil engineers and construction workers rely on this time for good visibility during early mornings or late evenings.

2. Nautical Twilight

• Occurs when the sun is 6° to 12° below the horizon.

• The horizon and some brighter stars are visible, aiding navigation at sea.

• Mariners use this twilight to determine their positions using the stars and horizon.

• Stargazers begin to observe brighter celestial objects during this phase.

3. Astronomical Twilight

• Happens when the sun is 12° to 18° below the horizon.

• The sky is dark enough for astronomers to observe faint celestial objects.

• Critical for astronomers as it marks the time when the sky is sufficiently dark for detailed observation.

• Astrophotography enthusiasts use this time to capture clear night skies.

How to Remember the Differences

• Civil Twilight: Practical, daily activities.

• Nautical Twilight: Sea navigation and basic stargazing.

• Astronomical Twilight: Ideal for astronomy and deep-sky observation.

Understanding the differences between these twilight phases enhances your appreciation of the night sky. Whether you're a sailor, stargazer, or someone planning an evening hike, knowing when each twilight occurs can make your activities more productive and enjoyable.

Remember to check a reliable sunrise and sunset calculator to determine the twilight times for your location!