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Understanding Twilight Phases and Their Times in the United States

June 17, 2026 · The Clime Team
Understanding Twilight Phases and Their Times in the United States

Twilight refers to the periods before sunrise and after sunset when the Sun is below the horizon, yet its light scatters through the atmosphere, illuminating the sky. This phenomenon is divided into three distinct phases: civil, nautical, and astronomical twilight. Each phase is characterized by the Sun's position relative to the horizon, affecting the amount of natural light available.

What Are the Different Twilight Phases?

Civil Twilight

Civil twilight occurs when the Sun is between the horizon and 6 degrees below it. During this time, there is enough natural light for most outdoor activities without artificial illumination. In the United States military, the terms "BMCT" (begin morning civil twilight) and "EECT" (end evening civil twilight) are used to denote the start of morning civil twilight and the end of evening civil twilight, respectively. (en.wikipedia.org)

Nautical Twilight

Nautical twilight occurs when the Sun is between 6 and 12 degrees below the horizon. During this phase, the horizon is still visible at sea, allowing sailors to take reliable star sightings for navigation. The terms "beginning of morning nautical twilight" and "end of evening nautical twilight" are used to denote the start and end of this phase, respectively. (preview.weather.gov)

Astronomical Twilight

Astronomical twilight occurs when the Sun is between 12 and 18 degrees below the horizon. During this phase, the sky is dark enough for astronomers to observe celestial objects without interference from the Sun's light. The terms "beginning of morning astronomical twilight" and "end of evening astronomical twilight" are used to denote the start and end of this phase, respectively. (preview.weather.gov)

How to Determine Twilight Times for Your Location

Twilight times vary based on geographic location and date. To find the specific times for civil, nautical, and astronomical twilight at your location, you can use online tools and resources. Websites like TimeandDate.com provide detailed sun and moon times, including twilight phases, for cities across the United States. By entering your city and date, you can access precise twilight times tailored to your location.

Why Are Twilight Times Important?

Understanding twilight times is essential for various activities:

  • Photography: The periods during civil twilight, known as the "golden hour," offer soft, diffused lighting ideal for capturing compelling images.

  • Navigation: Sailors and pilots rely on twilight phases, especially nautical twilight, for celestial navigation when the horizon is still visible.

  • Astronomy: Astronomers prefer astronomical twilight for observing celestial bodies without the interference of sunlight.

Conclusion

Twilight phases—civil, nautical, and astronomical—are integral to daily life, influencing activities from photography to navigation and astronomy. By understanding these phases and how to determine their times, you can plan your activities more effectively and appreciate the natural transitions of the day.

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