Twilight Times Calculator (Civil · Nautical · Astronomical)
All three twilight boundaries for any date and place — when to stop flying VFR, when the horizon vanishes at sea, when the stars switch fully on.
The boundaries earn their names: at civil dusk you stop reading outdoors and headlights become law in many places; at nautical dusk the sea horizon dissolves (no more sextant sights); at astronomical dusk the sky stops brightening the faintest stars. In mid-summer above ~49° latitude, astronomical twilight never ends — the 'grey nights' astronomers plan around.
Formula
⚠️ Ephemeris approximations (±1–3 min for sun times at mid-latitudes, ±0.5 day moon age) — ideal for planning; for precise almanac work use USNO/IMCCE data.
All three twilight boundaries for any date and place — when to stop flying VFR, when the horizon vanishes at sea, when the stars switch fully on.
About Twilight Times Calculator (Civil · Nautical · Astronomical)
Darkness arrives in three official installments: civil twilight ends when the sun reaches 6° below the horizon (outdoor work stops, headlights on), nautical at 12° (the sea horizon vanishes, ending sextant navigation), astronomical at 18° (skyglow from the sun finally zero — the astronomer's open-for-business sign). This calculator computes all three for any date and place, plus tomorrow's first light, by re-solving the sunrise equation at each depression angle.
How to use Twilight Times Calculator (Civil · Nautical · Astronomical)
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula same hour-angle solution at zenith 96° / 102° / 108° — sun 6°, 12°, 18° below the horizon substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Twilight Times Calculator (Civil · Nautical · Astronomical)?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula same hour-angle solution at zenith 96° / 102° / 108° — sun 6°, 12°, 18° below the horizon with sources cited on the page
- ✓The boundaries earn their names: at civil dusk you stop reading outdoors and headlights become law in many places; at nautical dusk the sea horizon dissolves (no more sextant sights); at astronomical dusk the sky stops brightening the faintest stars. In mid-summer above ~49° latitude, astronomical twilight never ends — the 'grey nights' astronomers plan around.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Who actually uses each twilight in the real world?+
Civil: aviation (VFR night rules and logging night time key on it in many jurisdictions), street-lighting contracts, hunting regulations, and 'legal darkness' in courts. Nautical: celestial navigation — the only window when both stars AND horizon are visible for sextant sights is between civil and nautical dusk (navigators call it, plainly, 'twilight'). Astronomical: observatory scheduling, astrophotography session planning, and dark-sky-reserve certification. Each is just a solar depression angle — 6, 12, 18 — applied to the same equation.
How long does full darkness take to arrive after sunset?+
Latitude and season decide: in the tropics the sun plunges perpendicular to the horizon and astronomical darkness lands 70–80 minutes after sunset year-round; at 45° it's 90–120 minutes; at 55°+ in summer it may never arrive (the sun bottoms out shallower than −18°). The planning rule for stargazers: true dark-sky targets need astronomical dusk, but the Milky Way becomes impressive by nautical dusk — meaning high-latitude summer astrophotography is a between-the-grey-nights sport, August to April.
Why does my phone's 'sunset' differ from when it actually gets dark?+
Because sunset is the BEGINNING of the dimming, not the end: at the −0.833° official sunset the illumination is still ~400 lux (easy reading); by civil dusk (−6°) it's ~3 lux (streetlight territory); nautical dusk ~0.01 lux; astronomical dusk matches moonless starlight at ~0.001 lux. The hour-plus between 'sunset' and felt darkness is twilight doing its logarithmic fade — five orders of magnitude of light loss that the single word 'sunset' flattens.
What are 'grey nights' and where do they happen?+
Summer nights where the sun never descends 18° below the horizon, so astronomical twilight persists from dusk to dawn: above ~48.6° latitude around the June solstice (Paris, Vancouver, Kyiv northward), the sky retains a permanent sun-glow on the northern horizon. Petersburg's celebrated 'white nights' (59.9°N) are the stronger version — civil twilight all night. The calculator returns '—' for boundaries the sun never crosses; that dash IS the grey-night diagnosis for your location and date.
Related Field tools
Sunrise & Sunset Calculator
Exact rise, set, solar noon and day length for any place and date — the NOAA solar equations with the refraction fine print included.
● LiveGolden Hour & Blue Hour Calculator
Tonight's golden hour and blue hour, computed from sun elevation — the photographer's light windows with the angles that define them.
● LiveDay Length Calculator
Hours of daylight for any date and latitude, how fast it's changing, and the swing between your solstices.
● Live