Twilight refers to the period of soft light before sunrise and after sunset, and it occurs every day at predictable times that depend on your location, season, and atmospheric conditions. Astronomers define twilight by the Sun’s position below the horizon, dividing it into civil, nautical, and astronomical phases based on how many degrees the Sun is below sea level. In everyday terms, twilight is the time between full daylight and complete darkness when the sky remains illuminated. This guide explains what time twilight sets each day, how the type and duration vary by geography and time of year, and how you can find precise twilight times for any place.
What Astronomers Mean by Twilight
Twilight is not an arbitrary label; it is a measurable interval defined by the Sun’s geometric position relative to the observer’s horizon. When the Sun is below the horizon but close to it, sunlight still illuminates the upper atmosphere, producing the characteristic glow. The official astronomical definitions break twilight into three stages based on how far the Sun is below the horizon. These stages have practical uses in fields such as aviation, photography, and astronomy, and they help standardize when twilight is considered to begin and end.
Civil, Nautical, and Astronomical Twilight
Civil twilight begins in the evening when the Sun is 0 to 6 degrees below the horizon and ends at sunset; in the morning it starts at sunset and ends when the Sun rises to 6 degrees below the horizon. During civil twilight, the horizon is still distinguishable, and bright stars and planets may become visible. Nautical twilight extends from 6 to 12 degrees below the horizon, a period used historically for navigation at sea when the horizon and some landmarks are faintly visible. Astronomical twilight spans 12 to 18 degrees below the horizon; it is the darkest form of twilight, after which the sky is essentially dark for astronomical observation. Each stage is roughly an hour long near the equator around the equinoxes, but this duration changes with latitude and time of year.
Why Twilight Times Change Daily
The time of twilight shifts each day because the Sun’s path across the sky changes with the seasons and varies by latitude. Earth’s axial tilt means that in summer the Sun sets at a shallower angle, lengthening twilight, while in winter the Sun drops more steeply, shortening it. In polar regions, twilight can last for many days or even weeks around the time of sunrise or sunset, especially outside the tropics. The exact moment of sunset also moves earlier or later by a few minutes each day, which shifts the twilight window accordingly. Atmospheric conditions such as elevation, cloud cover, and pollution can also affect how long twilight appears to last and how bright it seems.
How Twilight Set Depends on Location and Date
For any specific place, you can determine twilight times by calculating when the Sun reaches the relevant angles below the horizon. Near the equator, civil twilight may last only 20 to 30 minutes, while at higher latitudes in summer it can stretch to an hour or more. The dates of earliest sunset and latest sunrise do not align with the solstices in most mid-latitude locations, so twilight times can peak a little earlier or later than you might expect. In the tropics, twilight is often brief and fairly consistent year-round, whereas in higher latitudes it can vary dramatically between summer evenings and winter evenings.
Where to Find Exact Twilight Times
To find precise twilight times for your location, use astronomy websites or apps that let you enter a city or coordinates and return detailed tables for sunrise, sunset, and twilight stages. Many calendars and weather services also include twilight information, especially those aimed at photographers, astronomers, and outdoor planners. Keep in mind that published tables often list civil twilight times, and you may need to check for nautical or astronomical twilight if those are relevant to your plans. Because atmospheric refraction lifts the apparent position of the Sun by about half a degree, official twilight times are calculated using the geometric center of the Sun, adjusted for standard refraction.
Practical Uses of Knowing Twilight Times
Knowing when twilight occurs helps photographers plan lighting and exposure, allows astronomers to schedule observations, and assists travelers in planning safe arrival times at viewpoints or airports. For event organizers, understanding twilight can guide decisions on when to schedule outdoor ceremonies or concerts so that lighting is still adequate. In aviation, pilots and air traffic controllers refer to nautical and astronomical twilight for instrument checks and night operations definitions. Recreational hikers and runners also use twilight times to choose headlamp requirements and to avoid being out after full darkness in unfamiliar areas.
Quick Comparison of Twilight Types
| Twilight Type | Sun’s Position | Typical Duration Near Equinoxes (40° Latitude) | Common Use |
|---|---|---|---|
| Civil Twilight | 0 to 6 degrees below horizon | Roughly 1 hour total (30 minutes evening, 30 minutes morning) | Outdoor activities with natural light, photography with visible horizon |
| Nautical Twilight | 6 to 12 degrees below horizon | Roughly 1 hour total | Celestial navigation, transition to full night operations |
| Astronomical Twilight | 12 to 18 degrees below horizon | Roughly 1 hour total | Deep sky astronomy, full night sky conditions begin |
Special Cases and Long Twilight Periods
At high latitudes around the summer solstice, twilight can persist for many hours, sometimes overlapping with what would normally be nighttime. In the Arctic and Antarctic circles and nearby regions, the Sun may skim along the horizon for days, producing continuous twilight or even midnight sun with only brief periods of full darkness. Conversely, around the winter solstice, twilight can be extremely short or even absent if the Sun never rises above the horizon at all in polar night. In these regions, standard clock times for twilight become less meaningful, and users rely on solar or astronomical calculations tied to the local horizon.
How to Interpret Twilight Tables and Apps
When you read a table or app listing twilight times, check whether it is labeled as civil, nautical, or astronomical, and note whether the times are for sunrise or sunset. Some services provide a single time for evening twilight start, while others list separate starts and ends for each phase. If you need highly precise timing, such as for professional photography or research, use tools that account for atmospheric refraction, your exact elevation, and local horizon obstructions. Remember that published times are often rounded to the nearest minute, so you should allow a small buffer when planning activities that depend on accurate light conditions.