Civil twilight is the brightest phase of twilight, occurring when the sun sits between the horizon and 6 degrees below it. In practical terms, it’s the period just before sunrise and just after sunset when the sky is still bright enough to see your surroundings clearly without artificial light. It typically lasts about 20 to 40 minutes, depending on where you are on the planet and the time of year.
How Civil Twilight Is Defined
The U.S. Naval Observatory defines civil twilight as the period when the geometric center of the sun is between 0 and 6 degrees below the horizon. Morning civil twilight begins when the sun reaches that 6-degree mark and ends at sunrise. Evening civil twilight begins at sunset and ends when the sun drops to 6 degrees below the horizon.
During this window, the sky produces enough ambient light that terrestrial objects, buildings, trees, and landscape features are clearly distinguishable under good weather conditions. The horizon remains sharp and well-defined. Only the brightest stars and planets are visible overhead.
The Three Phases of Twilight
Civil twilight is one of three recognized phases, each defined by how far the sun has dipped below the horizon:
- Civil twilight: Sun is 0 to 6 degrees below the horizon. Outdoor visibility is good, and most activities can continue without artificial lighting.
- Nautical twilight: Sun is 6 to 12 degrees below the horizon. The horizon is still faintly visible at sea, which historically allowed sailors to take star-based navigation readings.
- Astronomical twilight: Sun is 12 to 18 degrees below the horizon. The sky appears nearly dark to the eye, but faint solar illumination still interferes with telescope observations of dim celestial objects.
Once the sun passes 18 degrees below the horizon, full night begins and the sky is completely dark (barring moonlight and light pollution).
Why the Sky Looks the Way It Does
The colors you see during civil twilight are driven by the way sunlight interacts with the atmosphere. Short-wavelength blue light scatters more easily off air molecules, a process called Rayleigh scattering. This is the same reason the daytime sky is blue, but during twilight the effect is amplified because sunlight enters the atmosphere at a steep angle and travels through a much thicker layer of air before reaching your eyes.
Near the horizon where the sun has just set, you’ll often see warm oranges and reds because the blue light has been scattered away during its long path through the atmosphere. Higher in the sky, the deeper blues dominate. Dust, pollution, and water droplets add a whitish glare near the horizon through a different scattering process that affects all wavelengths of light more equally. The result is that vivid gradient from warm tones near the horizon to deep blue overhead that photographers prize.
How Long It Lasts
The duration of civil twilight depends primarily on your latitude and the time of year. Near the equator, the sun drops almost straight down toward the horizon, passing through those 6 degrees quickly. Civil twilight there lasts roughly 20 to 24 minutes year-round.
At higher latitudes, the sun sets at a shallower angle, taking longer to travel the same 6 degrees. In the middle latitudes (around 40 to 50 degrees north or south), civil twilight lasts about 30 to 35 minutes. Near the summer solstice at very high latitudes, the sun may never dip more than 6 degrees below the horizon at all, creating a continuous civil twilight that lasts the entire night. This is what produces the famous “white nights” in cities like St. Petersburg and Reykjavik.
Civil Twilight in Aviation
Federal aviation regulations in the United States use civil twilight as the legal boundary between day and night flying. Under 14 CFR § 1.1, “night” is defined as the time between the end of evening civil twilight and the beginning of morning civil twilight. This distinction matters because night flying requires additional equipment, including position lights and anticollision lights, and pilots must meet specific recent-experience requirements before carrying passengers at night.
Recreational and sport pilots face stricter limits. Recreational certificate holders cannot fly between sunset and sunrise, and sport pilots cannot fly at night at all. For all other pilots, the shift from day to night operations triggers different fuel reserve requirements, instrument requirements, and logbook documentation rules. Pilots check published civil twilight times in the Air Almanac before every flight to determine which set of regulations applies.
Hunting and Shooting Hours
Many state and federal wildlife agencies tie legal shooting hours to civil twilight. A common framework allows hunters to begin shooting at morning civil twilight (roughly 30 minutes before sunrise) and requires them to stop at evening civil twilight (roughly 30 minutes after sunset). Alaska, for example, has proposed regulations making it unlawful to take big game between evening civil twilight and morning civil twilight in certain game management units. The logic is straightforward: civil twilight provides enough natural light for a hunter to clearly identify a target and what lies beyond it.
Visibility Is Not as Simple as It Seems
Civil twilight has traditionally been treated as a period with no meaningful restriction on normal outdoor activities. That characterization may be too generous for certain tasks. Research published in the journal Optometry and Vision Science found that while the light levels during civil twilight are sufficient for basic movement and spatial guidance, they selectively degrade your ability to recognize and identify objects. You can walk a path or steer a vehicle without difficulty, but picking out a pedestrian in dark clothing or reading a distant sign becomes harder than you might expect.
This distinction between “seeing enough to move” and “seeing enough to recognize” has real implications for traffic safety. The transition period around civil twilight consistently shows elevated rates of pedestrian-vehicle collisions, partly because drivers overestimate how well they can identify hazards in the fading light. If you’re driving during civil twilight, turning on your headlights early helps other drivers see you, even if you feel like you can still see the road just fine.
How to Find Civil Twilight Times
Civil twilight times change daily and vary by location. The simplest way to check is through weather apps, many of which list twilight times alongside sunrise and sunset. The U.S. Naval Observatory and the National Weather Service both publish tables with precise civil twilight times for any location and date. As a rough rule of thumb, civil twilight starts about 25 to 30 minutes before sunrise and ends about 25 to 30 minutes after sunset at mid-latitudes, but checking the actual published times is more reliable, especially if the distinction matters for flying, hunting, or photography.