Civil twilight, nautical twilight, and astronomical twilight explained
When the sun drops below the horizon, you don't go straight from "daytime" to "night." There's a gradual transition — twilight — that's actually divided into three formal stages by astronomers and navigators. Each stage has a precise definition and a specific look.
For sunrise/sunset and twilight times in any city, the sunrise-sunset page shows them.
The three stages
Twilight is defined by the sun's angle below the horizon:
| Stage | Sun's angle below horizon | What you can see |
|-------|---------------------------|------------------|
| Civil twilight | 0° to -6° | Bright enough to do most things outside without artificial light |
| Nautical twilight | -6° to -12° | Horizon still distinguishable from sky; first stars appear |
| Astronomical twilight | -12° to -18° | Most stars visible; only faintest objects remain hidden |
| Night | below -18° | Full darkness for astronomical observation |
The word "twilight" without qualification usually means civil twilight (the brightest, most usable stage).
Civil twilight (0° to -6°)
The brightest, most familiar twilight. Civil twilight begins immediately at sunset and ends when the sun is 6° below the horizon. Or in the morning, civil twilight begins when the sun is at -6° and ends at sunrise.
Civil twilight typically lasts 20-30 minutes at temperate latitudes. It's the period where:
- You can still read outdoors without lights
- Streetlights are typically just turning on
- Most outdoor activities can continue
- The horizon is clearly visible
In aviation, civil twilight is when most flights can still operate visually (VFR).
Common usage: "twilight" in a non-technical sense usually means civil twilight.
Nautical twilight (-6° to -12°)
Named because the horizon is still visible, allowing for celestial navigation by ship's officers. Nautical twilight is darker than civil but not yet "night."
During nautical twilight:
- Horizon still distinguishable from sky
- First stars and major planets become visible
- Difficult to read outdoors without artificial light
- Outdoor activities can continue but with care
- Common in coastal areas as "blue hour" begins
Nautical twilight is when many outdoor lights become necessary. Photographers' "blue hour" largely overlaps with nautical twilight.
Astronomical twilight (-12° to -18°)
The darkest formal twilight. Astronomical twilight ends when full astronomical darkness begins — when the sky is dark enough for serious astronomical observation.
During astronomical twilight:
- Most stars visible to the naked eye
- Faintest objects (like distant galaxies) still washed out by sky glow
- Outdoor activities require artificial light
- The sky may still appear slightly lighter than full night, especially toward the horizon
For amateur astronomers, the end of astronomical twilight is when "real" stargazing begins.
Why three stages?
Each stage has a specific use:
Civil twilight is defined for everyday activities — when do you need streetlights? When can you stop driving without headlights? Civil engineering and law often refer to civil twilight.
Nautical twilight is defined for navigation — when can sailors still see the horizon? Marine navigation uses this stage.
Astronomical twilight is defined for astronomy — when can researchers begin observations of faint objects?
The three definitions are coordinated globally. If a city's civil twilight ends at 6:30 PM, that's measurable and standardized.
How long does each stage last?
Duration depends on latitude and date:
At the equator: each stage lasts about 20 minutes year-round. Sunset is dramatic and brief.
Mid-latitudes (40° latitude): civil twilight ~25 min, nautical ~30 min, astronomical ~30 min in summer; shorter in winter.
High latitudes (60°+): dramatic seasonal variation. In summer, twilight lasts hours (or never fully ends). In winter, twilight can be very short.
Polar circles (66.5° N/S): in summer, the sun never drops 6° below — there's no astronomical night for weeks. The sky stays bright all "night."
In writing and photography
If you're a photographer or videographer:
- Golden hour = approximately civil twilight period (sun at -6° to +6°). The "warm light" period.
- Blue hour = approximately nautical twilight period (sun at -6° to -12°). Sky deepens to saturated blue.
- Astronomical twilight = "Milky Way appearing" period. Sky transitioning to full darkness.
For aurora viewing, you typically want astronomical darkness — full night, no twilight contamination.
For city night photography, nautical/civil twilight is often best — there's still some sky color, plus city lights.
Sunrise vs sunset twilight
The three stages exist symmetrically at sunrise:
Morning sequence:
- Astronomical twilight begins (sun at -18°): faint glow on eastern horizon
- Astronomical twilight ends (sun at -12°): horizon visible
- Nautical twilight ends (sun at -6°): nearly bright outdoors
- Civil twilight ends (sun at 0°): sunrise
Evening sequence (in reverse):
- Civil twilight begins (sun at 0°): sunset
- Nautical twilight begins (sun at -6°): horizon dimming
- Astronomical twilight begins (sun at -12°): mostly dark
- Astronomical twilight ends (sun at -18°): full night
The duration of each stage at sunset matches the corresponding sunrise stage.
How twilight affects daily life
You probably notice twilight without thinking about its formal stages:
- Streetlights turning on in early evening (during civil twilight)
- Car headlights coming on (start of civil twilight to start of nautical)
- "Dusk" generally refers to civil-to-nautical transition
- "Dawn" generally refers to nautical-to-civil transition
Different cultures and languages have different terms for these transitions; the formal three-stage system is more recent (19th century formalization) and most useful in scientific/navigational contexts.
Twilight at the poles
At the poles, "twilight" can mean very different things:
Summer (sun never sets): technically no twilight at all — the sun stays above the horizon. The sky may still get slightly dimmer near solar midnight, but it's not strictly twilight.
Winter (sun never rises): twilight occurs daily as the sun gets close to the horizon but doesn't cross. At the equinoxes (March and September), polar regions get brief twilight without sunrise/sunset.
Pole transitions: complicated; calculations require precise position information.
How to find twilight times for your city
Modern websites and apps:
- The sunrise-sunset page for your city shows civil twilight begin/end
- More specialized tools (like timeanddate.com) include all three stages
- Astronomy apps (like Stellarium) calculate them precisely
The data is reliable for any past or future date.
FAQ
What's the difference between civil twilight and golden hour?
Golden hour is roughly the period when the sun is between 0° and -6° (sunset side) or +6° (sunrise side). Civil twilight specifically refers to the post-sunset (or pre-sunrise) period. They overlap heavily but are not identical.
When can I see the most stars?
After astronomical twilight ends — full astronomical darkness. The sky is dark enough that even faint stars and galaxies are visible.
Why do photographers care about the three stages?
Each has a different lighting quality. Golden hour (approximately civil twilight) is warm and soft. Blue hour (approximately nautical) is deep blue with city lights starting to compete. Astronomical twilight is for star photography.
Does civil twilight always last 30 minutes?
No — duration depends on latitude and date. Equator: ~20 min. Mid-latitudes: 20-30 min. High latitudes: dramatically variable (hours in summer, minutes in winter).
What's "magic hour" in cinema?
Magic hour usually refers to golden hour + civil twilight combined — the period of soft, low-angle warm light just before sunset (or just after sunrise). It's brief but valuable for cinematography.
Can I see the Milky Way during nautical twilight?
Generally no — the sky is still too bright. The Milky Way becomes visible during astronomical twilight or full astronomical night.
Bottom line
Twilight has three formal stages defined by the sun's angle below the horizon: civil (0° to -6°, brightest), nautical (-6° to -12°, horizon still visible), and astronomical (-12° to -18°, most stars visible). Each has practical uses in everyday life, navigation, and astronomy.
For all twilight times in any city, the sunrise-sunset page calculates them.