What time does it actually get dark?

There are three answers, all correct. Civil twilight ends when the Sun is 6° below the horizon — that's when streetlights come on and you probably need a torch. Nautical twilight ends at 12° below, when the horizon becomes hard to see. Astronomical twilight ends at 18° below, and only after that is the sky fully dark for observing faint stars.

Why does 'dark' have three definitions?

The atmosphere keeps scattering sunlight long after the Sun has set. At 6° below, most artificial lights are needed. At 12° below, the horizon at sea is no longer usable for navigation. At 18° below, no more sunlight is reaching the upper atmosphere at all — that's the astronomer's definition of dark.

What is the blue hour?

The blue hour is the stretch of civil and early nautical twilight when the sky is a deep saturated blue but not yet black. It usually lasts 20–40 minutes after sunset (or before sunrise), and it's the best light for photography — long enough to work in, dark enough to see the horizon glow.

Why doesn't it get fully dark in summer at high latitudes?

If your latitude plus the Sun's declination puts the Sun less than 18° below the horizon even at midnight, astronomical night never happens. That's why summer nights in Norway, Scotland or Canada stay pale — the Sun is too shallow below the horizon for the sky to blacken.

How does daylight saving time affect it?

Clock changes shift what time it gets dark by exactly one hour but don't change the length of twilight — the Sun's altitude below the horizon is unchanged. Only your calendar time moves.

Do I need astronomical darkness to see the stars?

No. Bright stars, planets, the Moon and even the ISS are all visible during civil twilight. Astronomical darkness matters for faint objects — the Milky Way, deep-sky objects, faint meteors, and the aurora when it is weak.

Wide sky gradient from warm sunset through blue hour to deep indigo twilight

Sunset, twilight and darkness

Darkness has no single clock time — it depends entirely on your latitude and today's date.

What time does it get dark tonight?

Sunset, civil, nautical and astronomical dusk each arrive at different times depending on where you are on Earth. Set your location below and this page computes tonight's exact sequence for you.

Today's geometry · Monday 19 October

Why there is no single time it gets dark

The Sun's declination today is -9.8°, which fixes how steeply it drops below every horizon on Earth. Above 80° S it does not set at all. Everywhere else, darkness arrives in four stages — and the gap between them stretches with latitude.

Sunset

Sun 0°

The Sun's upper limb touches the horizon. Golden hour ends, blue hour begins.

Civil dusk

Sun −6°

Streetlights come on. Venus, Jupiter and the brightest stars appear.

Nautical dusk

Sun −12°

The sea horizon fades. Most naked-eye constellations are out.

Astronomical dark

Sun −18°

No sunlight reaches the upper atmosphere. Milky Way and faint meteors.

Reference examples only — computed for today on the Greenwich meridian (longitude 0°) and shown in UTC. These are **not** your times: your longitude and time zone shift every row. They are here to show how much latitude alone changes the answer.
Reference latitude	Sunset	Civil dusk	Nautical dusk	Astronomical dark	Sunset → dark
Equator (0°)	17:48	18:12	18:37	19:01	73 min
20° N	17:34	18:00	18:25	18:51	77 min
40° N	17:16	17:47	18:18	18:50	94 min
50° N	17:02	17:40	18:17	18:54	111 min
60° N	16:42	17:30	18:18	19:06	143 min
35° S	18:17	18:47	19:18	19:50	93 min

The stage definitions and the Sun's declination are global. Your own sunset, blue hour and the minute astronomical darkness begins depend on your latitude, longitude and time zone, so SnapCosmos computes them only for a location you actually give it — one tap below.

Location not set

Set a location for tonight's darkness time

Twilight length is a function of latitude and date. The same clock time is full darkness in one place and a bright sky in another.

Sunset and the end of each twilight stage
When astronomical darkness begins
Whether it gets fully dark at all tonight
How long the dark window lasts

Your choice stays in this browser. Nothing is sent to a SnapCosmos server.

Read

'Dark' has three definitions — all correct

Which one you care about depends on what you're trying to do.

Deep blue nautical twilight over a still lake with faint stars appearing

Nautical twilight — the blue hour has ended, the horizon has faded, and the first bright stars have arrived.

Civil twilight ends when the Sun is 6° below the horizon. This is the boundary where you start needing headlights on the road and streetlights come on automatically. The sky is a saturated blue — photographers call this the blue hour. You can already see Venus, Jupiter and the brightest handful of stars.

Nautical twilight ends at 12° below. Historically this was the point where the horizon at sea became indistinguishable from the sky — sailors could no longer use a sextant to fix stars against it. From land, this is when most of the naked-eye constellations are visible.

Astronomical twilight ends at 18° below. Only then is no sunlight reaching the upper atmosphere. This is what astronomers, aurora hunters and Milky Way photographers mean by dark. Faint meteors, weak aurora and deep-sky objects need this level of darkness to be seen properly.

At high latitudes in summer, astronomical night never happens — the Sun stays too shallow below the horizon for the sky to blacken. Norwegian summer nights are famously pale for this exact reason. It is not a defect; it is geometry.

After dark

What real astronomical darkness looks like

Once the Sun is 18° below the horizon, there is no residual sunlight in the sky. What you see instead is airglow — a permanent, faint greenish glow from oxygen and nitrogen molecules in the upper atmosphere — plus zodiacal light along the ecliptic, and, from a dark enough site, the full arch of the Milky Way stretching from horizon to horizon.

This is when meteor showers become worth staying up for, when aurora can be seen at lower activity levels, and when the faintest deep-sky objects — nebulae, distant galaxies, comets — reveal themselves. It is also when your eye's own dark adaptation reaches its full sensitivity, roughly 30 minutes after the last bright light.

Even the darkest astronomical night is not black. It is deep charcoal, textured, alive. The stars are unignorable. It is worth arranging your night around, if your latitude allows it.

A dark, star-filled sky with the Milky Way rising above a mountain silhouette

Astronomical night — Sun 18° below the horizon, no light pollution. The Milky Way is unignorable.

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