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When is it dark tonight?
For astrophotography, “dark” means astronomical night: the Sun is at least 18° below the horizon. Choose your location to see exactly when that starts and ends tonight, where the Moon is, and whether the weather is worth setting up for.
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The sky does not go from bright to dark the moment the Sun sets. It darkens in stages, named for how far the Sun is below the horizon.
- Civil twilight (Sun 0° to 6° below)
The sky is still bright and you can see bright stars and planets. A good time to unpack, level the tripod and polar align.
- Nautical twilight (6° to 12° below)
The horizon fades and more stars come out, but the sky is still too bright for faint deep-sky targets. Use the time for focusing and framing.
- Astronomical twilight (12° to 18° below)
Nearly dark. Bright targets and narrowband imaging can start here, but faint galaxies and nebulae look best once the Sun passes 18° and astronomical night begins.
The same stages run in reverse before sunrise. See the night timeline for all of them laid out hour by hour.
It depends on how steeply the Sun sets. Near the equator it drops almost straight down, so astronomical darkness arrives roughly 70 to 75 minutes after sunset. At 30° north (southern Texas, Florida) it takes about 80 minutes around the equinoxes and up to about 100 minutes in midsummer. At 40° north it is 90 minutes to 2 hours, and at 45° north it passes 2.5 hours in midsummer. The twilight stretches out in summer and at higher latitudes, because the Sun slides along the horizon instead of dropping below it.
Farther north than about 48° (or south, in the southern hemisphere), the Sun does not get 18° below the horizon for some weeks around midsummer. Astronomical night never happens then, and the sky stays in twilight until the Sun rises again.
Astronomical night only accounts for the Sun. A bright Moon adds its own glow and can wash out faint galaxies and nebulae for as long as it is up. Around new Moon the whole dark window is usable. Around full Moon the Moon is up for most of the night, leaving a few hours before moonrise or after moonset, or none.
Dark Window trims the dark window to the hours when the Moon is either down or thin enough not to matter. That is the “best imaging window” shown above. To plan ahead, the dark nights calendar shows the moon-free hours for the next 30 nights, and the light pollution guide covers the other half of “dark”: the sky glow from towns near you.
- When is it dark enough for astrophotography?
- For deep-sky imaging, when the Sun is at least 18 degrees below the horizon. That moment is called astronomical dusk, and the sky stays that dark until astronomical dawn. The exact times depend on your location and the date, and the tool above works them out for tonight.
- What time does astronomical darkness start tonight?
- Use the tool above for your exact time. As a rule of thumb it is about 1 hour 20 minutes to 1 hour 40 minutes after sunset in the southern United States, and 1.5 to 2.5 hours in the northern states. It is shorter nearer the equator, and longer in summer at higher latitudes.
- How long after sunset is it fully dark?
- Near the equator the Sun drops quickly, and full darkness arrives roughly 70 to 75 minutes after sunset. At 30° north, about the latitude of southern Texas and Florida, it takes 80 to 100 minutes depending on the season. At 40° north it takes 1.5 to 2 hours. The farther you are from the equator, and the closer to midsummer, the longer the twilight lasts.
- Why doesn't it get fully dark where I live in summer?
- Farther north than about 48 degrees latitude (and the same distance south), the Sun does not get 18 degrees below the horizon for some weeks around midsummer, so astronomical night never happens. The sky stays in twilight all night. Bright targets, the Moon, planets and narrowband imaging still work.
- What is the difference between civil, nautical and astronomical twilight?
- They are three steps in how far the Sun is below the horizon. Civil twilight is 0 to 6 degrees, when the sky is still bright and you can see bright stars and planets. Nautical twilight is 6 to 12 degrees, when the horizon fades. Astronomical twilight is 12 to 18 degrees, when the sky is nearly dark. After 18 degrees it is astronomical night.
- Does the Moon matter for when it is dark?
- The Moon does not change when astronomical night begins, but it can ruin the darkness. A bright Moon in the sky lights up the whole sky and washes out faint galaxies and nebulae. A new or thin crescent Moon leaves the whole dark window usable, while a full Moon can leave only a few hours before moonrise or after moonset.
- Is tonight good for astrophotography?
- It takes darkness and a clear sky. Darkness depends on the Sun and Moon, which this page shows. Clear sky depends on cloud, and also on seeing and transparency. The Dark Window planner combines all of them into a GO, MARGINAL or NO-GO verdict for your location.
Open the Dark Window planner for the full GO / NO-GO forecast, hour-by-hour weather and targets that fit your telescope.